119 results on '"Sudha Mokkapati"'
Search Results
2. Self-powered MoSe2/ZnO heterojunction photodetectors with current rectification effect and broadband detection
- Author
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Zhichen Wan, Haoran Mu, Zhuo Dong, Sigui Hu, Wenzhi Yu, Shenghuang Lin, and Sudha Mokkapati
- Subjects
Van der Waals ,Molybdenum disulphide ,Zinc oxide ,Self-powered photodetector ,Materials of engineering and construction. Mechanics of materials ,TA401-492 - Abstract
Recently, n-n junction with large bandgap offset has been reported to be able to realize rectifier function and improve photoresponse in optoelectronic applications. In this work, we demonstrate a simple way to engineer photodetector based on a MoSe2/ZnO heterojunction. ZnO thin film deposited by DC magnetron sputtering and mechanically exfoliated MoSe2 was coupled to form vertical stacking heterostructure. An atomically sharp n-n junction with type-II band alignment and current rectification behaviour is realised. The MoSe2/ZnO based photodetector exhibits a fast photoresponse speed of 40 μs, and a peak responsivity of 2.7 A/W. It is also demonstrated that the MoSe2/ZnO photodiode can operate under self-powered mode over a broad spectrum.
- Published
- 2021
- Full Text
- View/download PDF
3. Ultra-broadband photodetection based on two-dimensional layered Ta2NiSe5 with strong anisotropy and high responsivity
- Author
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Yan Zhang, Wenzhi Yu, Jie Li, Jie Chen, Zhuo Dong, Liu Xie, Chang Li, Xinyao Shi, Wanlong Guo, Shenghuang Lin, Sudha Mokkapati, and Kai Zhang
- Subjects
2D materials ,Photoconductive ,Broadband ,Photodetector ,Anisotropic ,Materials of engineering and construction. Mechanics of materials ,TA401-492 - Abstract
Broadband photodetectors have attracted substantial attention in recent years. The ternary chalcogenide Ta2NiSe5 is a layered material with a direct narrow-band gap (Eg ~ 0.33 eV) which possesses greatly potential to broadband photodetectors. Here, high-quality bulk Ta2NiSe5 was synthesized by Chemical Vapor Transport (CVT) method. We demonstrate a photodetector based on exfoliated Ta2NiSe5 nanoflake, which exhibits a broadband photo-response from 405 nm to 4300 nm. Meanwhile, its main characteristics are superior to other typical 2D materials: high responsivity ~198.1 A W−1 at 1350 nm and ultrafast response time of ~27.4 µs. Long-time photocurrent reproducibility shows that the photodetector has excellent stability under atmosphere. Furthermore, the scanning photocurrent mapping reveals the photoconductive mechanism of Ta2NiSe5 photodetector. In addition, the anisotropic ratio of the photocurrent is ~1.46. The broadband photodetection, high responsivity, anisotropic and environmental stability achieved simultaneously in Ta2NiSe5 photodetector, which are promising for neotype electronics and optoelectronics field.
- Published
- 2021
- Full Text
- View/download PDF
4. Doping-enhanced radiative efficiency enables lasing in unpassivated GaAs nanowires
- Author
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Tim Burgess, Dhruv Saxena, Sudha Mokkapati, Zhe Li, Christopher R. Hall, Jeffrey A. Davis, Yuda Wang, Leigh M. Smith, Lan Fu, Philippe Caroff, Hark Hoe Tan, and Chennupati Jagadish
- Subjects
Science - Abstract
Until now, efforts to enhance the performance of nanolasers have focused on reducing the rate of non-radiative recombination. Here, Burgess et al.employ controlled impurity doping to increase the rate of radiative recombination.
- Published
- 2016
- Full Text
- View/download PDF
5. Wafer-Scale Synthesis of 2D Dirac Heterostructures for Self-Driven, Fast, Broadband Photodetectors
- Author
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Wenzhi Yu, Zhuo Dong, Haoran Mu, Guanghui Ren, Xiaoyue He, Xiu Li, Shenghuang Lin, Kai Zhang, Qiaoliang Bao, and Sudha Mokkapati
- Subjects
General Engineering ,General Physics and Astronomy ,General Materials Science - Abstract
Type-II Dirac semimetal platinum ditelluride (PtTe
- Published
- 2022
6. Managing Resonant and Nonresonant Lasing Modes in GaAs Nanowire Random Lasers
- Author
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Sudha Mokkapati, Hark Hoe Tan, Zhicheng Su, Mohammad Rashidi, Tuomas Haggren, and Chennupati Jagadish
- Subjects
Materials science ,Scattering ,business.industry ,Mechanical Engineering ,Nanowire ,Physics::Optics ,Bioengineering ,02 engineering and technology ,General Chemistry ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Laser ,law.invention ,Quality (physics) ,law ,Excited state ,Optoelectronics ,General Materials Science ,0210 nano-technology ,business ,Lasing threshold - Abstract
Random lasers are promising, easy-to-fabricate light sources that rely on scattering instead of well-defined optical cavities. We demonstrate random lasing in GaAs nanowires using both randomly oriented and vertically aligned arrays. These configurations are shown to lase in both resonant and nonresonant modes, where aligned nanowires support predominantly resonant lasing and randomly oriented favors nonresonant lasing. On the basis of numerical simulations, aligning the nanowires increases the system's scattering efficiency leading to higher quality factor modes and thus favoring the resonant modes. We further demonstrate two methods to optically suppress resonant mode lasing by increasing the number of excited modes. The light output-light input curves show a pronounced kink for the resonant lasing mode while the nonresonant mode is kink-free. The resonant lasing modes may be used as tunable lasers, and the nonresonant modes exhibit near-thresholdless amplification. Switching between lasing modes opens up new opportunities to use lasers in broader applications.
- Published
- 2021
7. Anderson localization of light in InP nanowires for stable, multimode lasing
- Author
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Sudha Mokkapati, Hark Hoe Tan, and Mohammad Rashidi
- Subjects
Anderson localization ,Multi-mode optical fiber ,Materials science ,business.industry ,Nanowire ,Optoelectronics ,business ,Lasing threshold - Published
- 2021
8. Controling the type of lasing modes in disordered media based on GaAs-AlGaAs nanowires
- Author
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Zhicheng Su, Tuomas Haggren, Mohammad Rashidi, Hark Hoe Tan, Chennupati Jagadish, and Sudha Mokkapati
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Materials science ,business.industry ,Nanowire ,Physics::Optics ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Laser ,law.invention ,law ,Optoelectronics ,Physics::Atomic Physics ,Photonics ,business ,Gaas algaas ,Lasing threshold - Abstract
Random lasers lase in two types of modes: resonant and nonresonant modes. The resonant modes could be used in tunable lasers while the nonresonant modes could lase at low thresholds. Here, methods to manage modes in nanowires based random lasers are shown and discussed.
- Published
- 2021
9. Ultra-broadband photodetection based on two-dimensional layered Ta2NiSe5 with strong anisotropy and high responsivity
- Author
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Wanlong Guo, Jie Chen, Chang Li, Wenzhi Yu, Sudha Mokkapati, Liu Xie, Kai Zhang, Shenghuang Lin, Xinyao Shi, Jie Li, Zhuo Dong, and Yan Zhang
- Subjects
Materials science ,Photodetector ,Broadband ,02 engineering and technology ,Photodetection ,010402 general chemistry ,01 natural sciences ,Responsivity ,General Materials Science ,Photoconductive ,Anisotropy ,Materials of engineering and construction. Mechanics of materials ,Photocurrent ,business.industry ,Mechanical Engineering ,Photoconductivity ,Anisotropic ,021001 nanoscience & nanotechnology ,2D materials ,0104 chemical sciences ,Mechanics of Materials ,TA401-492 ,Optoelectronics ,0210 nano-technology ,business ,Ultrashort pulse - Abstract
Broadband photodetectors have attracted substantial attention in recent years. The ternary chalcogenide Ta2NiSe5 is a layered material with a direct narrow-band gap (Eg ~ 0.33 eV) which possesses greatly potential to broadband photodetectors. Here, high-quality bulk Ta2NiSe5 was synthesized by Chemical Vapor Transport (CVT) method. We demonstrate a photodetector based on exfoliated Ta2NiSe5 nanoflake, which exhibits a broadband photo-response from 405 nm to 4300 nm. Meanwhile, its main characteristics are superior to other typical 2D materials: high responsivity ~198.1 A W−1 at 1350 nm and ultrafast response time of ~27.4 µs. Long-time photocurrent reproducibility shows that the photodetector has excellent stability under atmosphere. Furthermore, the scanning photocurrent mapping reveals the photoconductive mechanism of Ta2NiSe5 photodetector. In addition, the anisotropic ratio of the photocurrent is ~1.46. The broadband photodetection, high responsivity, anisotropic and environmental stability achieved simultaneously in Ta2NiSe5 photodetector, which are promising for neotype electronics and optoelectronics field.
- Published
- 2021
10. Ultrathin Ta2O5 electron-selective contacts for high efficiency InP solar cells
- Author
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Hark Hoe Tan, Sudha Mokkapati, Siva Krishna Karuturi, Chennupati Jagadish, Kaushal Vora, Mykhaylo Lysevych, Yiliang Wu, Yimao Wan, Jennifer Wong-Leung, and Parvathala Reddy Narangari
- Subjects
Materials science ,Photoluminescence ,Organic solar cell ,business.industry ,Open-circuit voltage ,Doping ,Heterojunction ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,law.invention ,Atomic layer deposition ,law ,Solar cell ,Optoelectronics ,General Materials Science ,0210 nano-technology ,business ,Short circuit - Abstract
Heterojunction solar cells with transition-metal–oxide-based carrier-selective contacts have been gaining considerable research interest owing to their amenability to low-cost fabrication methods and elimination of parasitic absorption and complex semiconductor doping process. In this work, we propose tantalum oxide (Ta2O5) as a novel electron-selective contact layer for photo-generated carrier separation in InP solar cells. We confirm the electron-selective properties of Ta2O5 by investigating band energetics at the InP–Ta2O5 interface using X-ray photoelectron spectroscopy. Time-resolved photoluminescence and power dependent photoluminescence reveal that the Ta2O5 inter-layer also mitigates parasitic recombination at the InP/transparent conducting oxide interface. With an 8 nm Ta2O5 layer deposited using an atomic layer deposition (ALD) system, we demonstrate a planar InP solar cell with an open circuit voltage, Voc, of 822 mV, a short circuit current density, Jsc, of 30.1 mA cm−2, and a fill factor of 0.77, resulting in an overall device efficiency of 19.1%. The Voc is the highest reported value to date for an InP heterojunction solar cells with carrier-selective contacts. The proposed Ta2O5 material may be of interest not only for other solar cell architectures including perovskite cells and organic solar cells, but also across a wide range of optoelectronics applications including solid state emitting devices, photonic crystals, planar light wave circuits etc.
- Published
- 2019
11. Efficient and Tunable Reflection of Phonon Polaritons at Built-In Intercalation Interfaces
- Author
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Qiaoliang Bao, Zhigao Dai, Michael S. Fuhrer, Yingjie Wu, Sudha Mokkapati, Cheng-Wei Qiu, Shaohua Dong, Guangyuan Si, Guangwei Hu, and Qingdong Ou
- Subjects
Condensed Matter::Quantum Gases ,Materials science ,Condensed matter physics ,Phonon ,Mechanical Engineering ,Phase (waves) ,Nanophotonics ,Physics::Optics ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,symbols.namesake ,Reflection (mathematics) ,Mechanics of Materials ,symbols ,Polariton ,General Materials Science ,van der Waals force ,0210 nano-technology ,Anisotropy ,Plasmon - Abstract
Phonon polaritons-light coupled to lattice vibrations-in polar van der Waals crystals offer unprecedented opportunities for controlling light at the nanoscale due to their anisotropic and ultralow-loss propagation. While their analog plasmon polaritons-light coupled to electron oscillations-have long been studied and exhibit interesting reflections at geometrical edges and electronic boundaries, whether phonon polaritons can be reflected by such barriers has been elusive. Here, the effective and tunable reflection of phonon polaritons at embedded interfaces formed in hydrogen-intercalated α-MoO3 flakes is elaborated upon. Without breaking geometrical continuity, such intercalation interfaces can reflect phonon polaritons with low losses, yielding the distinct phase changes of -0.8π and -0.3π associated with polariton propagation, high efficiency of 50%, and potential electrical tunability. The results point to a new approach to construct on-demand polariton reflectors, phase modulators, and retarders, which may be transplanted into building future polaritonic circuits using van der Waals crystals.
- Published
- 2021
12. Engineering Micro-disk Resonators for Coupling to Dark and Bright Excitons in 2D Materials
- Author
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Lekshmi Eswaramoorthy, Sudha Mokkapati, and Anshuman Kumar
- Abstract
The coupling efficiency of a micro-disk with the dark excitons in an atomically thin semiconductor is strengthened by Purcell enhanced out-of-plane resonator modes. This work proposes the engineering of these modes through the tapered disks.
- Published
- 2021
13. Selective Coupling of Dark and Bright Excitons in 2D Transition Metal Dichalcogenide Alloys to Planar Microstructures
- Author
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Lekshmi Eswaramoorthy, Brijesh Kumar, Sudha Mokkapati, and Anshuman Kumar
- Abstract
We present a route to selective coupling of dark and bright excitons in atomically thin transition metal dichalcogenide alloys to planar microstructures via anisotropic Purcell enhanced out-of-plane resonator modes engineered by tapering of micro-disks.
- Published
- 2021
14. Self-powered MoSe2/ZnO heterojunction photodetectors with current rectification effect and broadband detection
- Author
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Wenzhi Yu, Sigui Hu, Zhichen Wan, Haoran Mu, Shenghuang Lin, Sudha Mokkapati, and Zhuo Dong
- Subjects
Materials science ,business.industry ,Band gap ,Mechanical Engineering ,Self-powered photodetector ,Photodetector ,Heterojunction ,Sputter deposition ,Photodiode ,law.invention ,Responsivity ,Rectification ,Mechanics of Materials ,law ,Zinc oxide ,TA401-492 ,Optoelectronics ,Van der Waals ,General Materials Science ,Thin film ,business ,Materials of engineering and construction. Mechanics of materials ,Molybdenum disulphide - Abstract
Recently, n-n junction with large bandgap offset has been reported to be able to realize rectifier function and improve photoresponse in optoelectronic applications. In this work, we demonstrate a simple way to engineer photodetector based on a MoSe2/ZnO heterojunction. ZnO thin film deposited by DC magnetron sputtering and mechanically exfoliated MoSe2 was coupled to form vertical stacking heterostructure. An atomically sharp n-n junction with type-II band alignment and current rectification behaviour is realised. The MoSe2/ZnO based photodetector exhibits a fast photoresponse speed of 40 μs, and a peak responsivity of 2.7 A/W. It is also demonstrated that the MoSe2/ZnO photodiode can operate under self-powered mode over a broad spectrum.
- Published
- 2021
15. Controlling the lasing modes in random lasers operating in the Anderson localization regime
- Author
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Ziyuan Li, Sudha Mokkapati, Chennupati Jagadish, Mohammad Rashidi, and Hark Hoe Tan
- Subjects
Physics ,Anderson localization ,business.industry ,Scattering ,Filling factor ,Nanowire ,Physics::Optics ,Laser ,Atomic and Molecular Physics, and Optics ,law.invention ,Optics ,law ,Optoelectronics ,Whispering-gallery wave ,business ,Lasing threshold ,Randomness - Abstract
Random lasers, which rely on random scattering events unlike traditional Fabry-Pérot cavities, are much simpler and cost-effective to fabricate. However, because of the chaotic fluctuations and instability of the lasing modes, controlling the lasing properties is challenging. In this study, we use random InP nanowire (NW) arrays that operate in the Anderson localization regime with stable modes as the random lasers. We show that by changing the design parameters of the NW arrays, such as filling factor, dimensions of the NWs, degree of randomness, and the size of the array, the properties of the lasing modes including the number of modes, lasing wavelengths, and lasing threshold can be controlled.
- Published
- 2021
16. Stable, multi-mode lasing in the strong localization regime from InP random nanowire arrays at low temperature
- Author
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Sudha Mokkapati, Hark Hoe Tan, and Mohammad Rashidi
- Subjects
Materials science ,Scattering ,business.industry ,Nanowire ,Physics::Optics ,Laser ,Stability (probability) ,Instability ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,law.invention ,Wavelength ,Quality (physics) ,law ,Optoelectronics ,business ,Lasing threshold - Abstract
Disorder is generally considered an undesired element in lasing action. However, in random lasers whose feedback mechanism is based on random scattering events, disorder plays a very important and critical role. Even though some unique properties in random lasers such as large-angle emission, lasing from different surfaces, large-area manufacturability, and wavelength tunability can be advantageous in certain applications, the applicability of random lasers has been limited due to the chaotic fluctuations and instability of the lasing modes because of weak confinement. To solve this, mode localization could reduce the spatial overlap between lasing modes, thus preventing mode competition and improving stability, leading to laser sources with high quality factors and very low thresholds. Here, by using a random array of III-V nanowires, high-quality-factor localized modes are demonstrated. We present the experimental evidence of strong light localization in multi-mode random nanowire lasers which are temporally stable at low temperatures.
- Published
- 2021
17. Ultrasensitive WSe2 field-effect transistor-based biosensor for label-free detection of cancer in point-of-care applications
- Author
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Wenzhi Yu, Vaishnavi Krishnamurthi, Sumeet Walia, Qiaoliang Bao, Yingjie Wu, Tuncay Alan, Hemayet Uddin, Nasir Mahmood, Sudha Mokkapati, Mohammad Mosarof Hossain, and Babar Shabbir
- Subjects
Materials science ,Mechanical Engineering ,Cancer ,Nanotechnology ,General Chemistry ,Condensed Matter Physics ,medicine.disease ,Prostate cancer ,Mechanics of Materials ,medicine ,General Materials Science ,Field-effect transistor ,Biosensor ,Label free ,Point of care - Published
- 2021
18. Ultrathin Ta
- Author
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Parvathala Reddy, Narangari, Siva Krishna, Karuturi, Yiliang, Wu, Jennifer, Wong-Leung, Kaushal, Vora, Mykhaylo, Lysevych, Yimao, Wan, Hark Hoe, Tan, Chennupati, Jagadish, and Sudha, Mokkapati
- Abstract
Heterojunction solar cells with transition-metal-oxide-based carrier-selective contacts have been gaining considerable research interest owing to their amenability to low-cost fabrication methods and elimination of parasitic absorption and complex semiconductor doping process. In this work, we propose tantalum oxide (Ta2O5) as a novel electron-selective contact layer for photo-generated carrier separation in InP solar cells. We confirm the electron-selective properties of Ta2O5 by investigating band energetics at the InP-Ta2O5 interface using X-ray photoelectron spectroscopy. Time-resolved photoluminescence and power dependent photoluminescence reveal that the Ta2O5 inter-layer also mitigates parasitic recombination at the InP/transparent conducting oxide interface. With an 8 nm Ta2O5 layer deposited using an atomic layer deposition (ALD) system, we demonstrate a planar InP solar cell with an open circuit voltage, Voc, of 822 mV, a short circuit current density, Jsc, of 30.1 mA cm-2, and a fill factor of 0.77, resulting in an overall device efficiency of 19.1%. The Voc is the highest reported value to date for an InP heterojunction solar cells with carrier-selective contacts. The proposed Ta2O5 material may be of interest not only for other solar cell architectures including perovskite cells and organic solar cells, but also across a wide range of optoelectronics applications including solid state emitting devices, photonic crystals, planar light wave circuits etc.
- Published
- 2019
19. Axial p-n junction design and characterization for InP nanowire array solar cells
- Author
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Lan Fu, Yanan Guo, Hark Hoe Tan, Ziyuan Li, Yesaya C. Wenas, Zhe Li, Ahmed Alabadla, Li Li, F Fouad Karouta, Kun Peng, Kaushal Vora, Fan Wang, Qian Gao, Sudha Mokkapati, and Chennupati Jagadish
- Subjects
Materials science ,Renewable Energy, Sustainability and the Environment ,business.industry ,Doping ,Nanowire ,02 engineering and technology ,Substrate (electronics) ,Electron ,Sputter deposition ,Electroluminescence ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,Characterization (materials science) ,Optoelectronics ,Electrical and Electronic Engineering ,0210 nano-technology ,business ,p–n junction - Abstract
In this work, InP nanowire (NW) array solar cells with different axial p‐i‐n junction designs were investigated. The optical properties of the different NW structures were characterized through a series of microphotoluminescence measurements to extract important material parameters such as minority carrier lifetimes and internal quantum efficiencies. A glancing angle sputtering deposition technique has been developed to enable a direct visualization of the p‐n junctions in the vertical array of InP NW solar cells (NWSCs) using electron beam‐induced current (EBIC) technique. Based on EBIC and electrical simulation, it is found that the background doping in NWSC significantly affects the junction position. By modifying the junction design, the width and position of the p‐n junction can be varied effectively. By employing a p‐p−‐n structure, a high junction position (>1 μm from the substrate) and wide depletion width have been achieved as confirmed by EBIC measurement. Moreover, the NW growth substrate does not show any influence on the device behavior due to the fully decoupled junction position, indicating a promising structural design for future development of high‐performance, low‐cost flexible NW devices.
- Published
- 2019
20. Optical study of p-doping in GaAs nanowires for low-threshold and high-yield lasing
- Author
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Chennupati Jagadish, Alex S. Walton, Stefan Skalsky, Tim Burgess, Patrick Parkinson, Peter Mitchell, Sudha Mokkapati, Juan Arturo Alanis, Dhruv Saxena, Mykhaylo Lysevych, Xiaoyan Tang, and Hark Hoe Tan
- Subjects
PL ,Materials science ,ResearchInstitutes_Networks_Beacons/photon_science_institute ,Nanowire ,Physics::Optics ,Bioengineering ,02 engineering and technology ,Photon Science Institute ,Condensed Matter::Materials Science ,Doping ,General Materials Science ,Spontaneous emission ,III-V Nanowire lasers ,business.industry ,Mechanical Engineering ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Semiconductor ,Yield (chemistry) ,Optoelectronics ,Quantum efficiency ,0210 nano-technology ,business ,Lasing threshold ,Recombination - Abstract
Semiconductor nanowires suffer from significant non-radiative surface recombination, however, heavy p-type doping has proven to be a viable option to increase the radiative recombination rate and hence quantum efficiency of emission, allowing demonstration of room-temperature lasing. Using a large-scale optical technique, we have studied Zn-doped GaAs nanowires to understand and quantify the effect of doping on growth and lasing properties. We measure the non-radiative recombination rate (knr) to be (0.14 ± 0.04) ps−1 by modelling the internal quantum efficiency (IQE) as a function of doping level. By applying a correlative method, we identify doping and nanowire length as key controllable parameters determining lasing behavior, with reliable room-temperature lasing occurring for p &3 × 1018 cm−3 and lengths & 4 µm. We report a best-in-class core-only near-infrared nanowire lasing threshold of ∼ 10 µJ cm−2 , and using a data-led filtering step, we present a method to simply identify sub-sets of nanowires with over 90% lasing yield.
- Published
- 2018
21. Efficiency enhancement of axial junction InP single nanowire solar cells by dielectric coating
- Author
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Chennupati Jagadish, Li Li, Guojun Zhang, Lan Fu, Zhe Li, Kun Peng, Zhiming Wang, Zhiqin Zhong, Hark Hoe Tan, Jiang Wu, Ziyuan Li, Qian Gao, Kaushal Vora, and Sudha Mokkapati
- Subjects
Photocurrent ,Materials science ,Passivation ,Renewable Energy, Sustainability and the Environment ,business.industry ,Electron beam-induced current ,Energy conversion efficiency ,food and beverages ,02 engineering and technology ,Quantum dot solar cell ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Polymer solar cell ,0104 chemical sciences ,law.invention ,Surface coating ,law ,Solar cell ,Optoelectronics ,General Materials Science ,Electrical and Electronic Engineering ,0210 nano-technology ,business - Abstract
In this work we demonstrate single axial p-i-n junction InP nanowire (NW) solar cells grown by selective-area metal organic vapor phase epitaxy (SA-MOVPE) technique. A power conversion efficiency of up to 6.5% was realized in the single NW solar cell (horizontally lying on substrate) without any surface passivation. Electron beam induced current (EBIC) and photocurrent mapping were performed to investigate the electrical properties of the NW solar cells and their influence on device performance, which are essential for an in-depth understanding of the design requirements for NW solar cells. A further conformal SiNx layer was deposited on the single NW solar cell devices by plasma-enhanced chemical vapor deposition (PECVD). Overall efficiency improvement has been obtained in the SiNx-coated devices with a remarkable up to 62% increase to a peak efficiency of 10.5%, which to our knowledge is the highest efficiency reported for horizontal single NW solar cells. This has been attributed to an enhanced optical antenna effect and effective surface passivation due to SiNx coating, as respectively confirmed by numerical simulation and time-resolved photoluminescence (TRPL) measurements. Our work demonstrates that dielectric coating is a promising simple approach to achieve high performance III–V NW solar cells.
- Published
- 2016
22. Characterizing amorphous silicon, silicon nitride, and diffused layers in crystalline siliconsolarcellsusingmicro-photoluminescence spectroscopy
- Author
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Stefaan De Wolf, Di Yan, Silvia Martin de Nicolas, Hieu T. Nguyen, Daniel Macdonald, Yimao Wan, Sudha Mokkapati, Johannes P. Seif, and Fiacre Rougieux
- Subjects
010302 applied physics ,Amorphous silicon ,Materials science ,Silicon ,Renewable Energy, Sustainability and the Environment ,business.industry ,Nanocrystalline silicon ,chemistry.chemical_element ,Strained silicon ,02 engineering and technology ,Substrate (electronics) ,021001 nanoscience & nanotechnology ,01 natural sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Monocrystalline silicon ,chemistry.chemical_compound ,chemistry ,Silicon nitride ,0103 physical sciences ,Optoelectronics ,Crystalline silicon ,0210 nano-technology ,business - Abstract
We report and explain the photoluminescence (PL) spectra from crystalline silicon (c-Si) wafers passivated by hydrogenated amorphous silicon (a-Si:H) films under various measurement conditions, utilizing the different absorption coefficients and radiative recombination mechanisms in c-Si and a-Si:H. By comparison with the luminescence properties of a-Si:H, we also demonstrate that SiNx films deposited under certain silicon-rich conditions yield luminescence spectra similar to those of a-Si:H, indicating the presence of an a-Si:H-like phase in the SiNx films. This causes a reduction in the blue response of the solar cells via parasitic absorption. In addition, with the ability to detect the specific emission from heavily-doped silicon via band-gap narrowing effects, we can unambiguously separate individual spectral PL signatures of three different layers in a single substrate: the SiNx passivation films, the diffused layers, and the underlying c-Si substrate. Finally, we apply this technique to evaluate parasitic absorption in the passivation films, and the doping density of the diffused layers on different finished solar cells, highlighting the value of this nondestructive contactless, micron-scale technique for photovoltaic applications.
- Published
- 2016
23. Tantalum Oxide Electron-Selective Heterocontacts for Silicon Photovoltaics and Photoelectrochemical Water Reduction
- Author
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Yimao Wan, Andres Cuevas, Chennupati Jagadish, Di Yan, Jun Peng, Mark Hettick, Hark Hoe Tan, Parvathala Reddy Narangari, Ali Javey, Sudha Mokkapati, Christian Samundsett, James Bullock, and Siva Krishna Karuturi
- Subjects
Materials science ,Silicon ,Passivation ,Energy Engineering and Power Technology ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,7. Clean energy ,Atomic layer deposition ,Affordable and Clean Energy ,Photovoltaics ,Materials Chemistry ,Crystalline silicon ,QC ,Renewable Energy, Sustainability and the Environment ,business.industry ,Photovoltaic system ,Energy conversion efficiency ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Fuel Technology ,chemistry ,Chemistry (miscellaneous) ,Optoelectronics ,Water splitting ,0210 nano-technology ,business - Abstract
Crystalline silicon (c-Si) solar cells have been dominating the photovoltaic (PV) market for decades, and c-Si based photoelectrochemical (PEC) cells are regarded as one of the most promising routes for water splitting and renewable production of hydrogen. In this work, we demonstrate a nanoscale tantalum oxide (TaOx, ∼6 nm) as an electron-selective heterocontact, simultaneously providing high-quality passivation to the silicon surface and effective transport of electrons to either an external circuit or a water-splitting catalyst. The PV application of TaOx is demonstrated by a proof-of-concept device having a conversion efficiency of 19.1%. In addition, the PEC application is demonstrated by a photon-to-current efficiency (with additional applied bias) of 7.7%. These results represent a 2% and 3.8% absolute enhancement over control devices without a TaOx interlayer, respectively. The methods presented in this Letter are not limited to c-Si based devices and can be viewed as a more general approach to the interface engineering of optoelectronic and photoelectrochemical applications.
- Published
- 2018
24. Preface
- Author
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Sudha Mokkapati and Chennupati Jagadish
- Published
- 2018
25. Nanowires for Energy Applications
- Author
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Sudha Mokkapati, Chennupati Jagadish, Sudha Mokkapati, and Chennupati Jagadish
- Subjects
- Nanowires
- Abstract
Nanowires for Energy Applications, Volume 98, covers the latest breakthrough research and exciting developments in nanowires for energy applications. This volume focuses on various aspects of Nanowires for Energy Applications, presenting interesting sections on Electrospun semiconductor metal oxide nanowires for energy and sensing applications, Integration into flexible and functional materials, Nanowire Based Bulk Heterojunction Solar Cells, Semiconductor Nanowires for Thermoelectric Generation, Energy Scavenging: Mechanical, Thermoelectric, and Nanowire synthesis/growth methods, and more. - Features the latest breakthroughs and research and development in nanowires for energy applications - Covers a broad range of topics, including a wide variety of materials and many important aspects of solar fuels - Includes in-depth discussions on materials design, growth and synthesis, engineering, characterization and photoelectrochemical studies
- Published
- 2018
26. Mode Profiling of Semiconductor Nanowire Lasers
- Author
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Sudha Mokkapati, Dhruv Saxena, Fan Wang, Qian Gao, Chennupati Jagadish, and Hark Hoe Tan
- Subjects
Profiling (computer programming) ,Materials science ,business.industry ,Mechanical Engineering ,Spatially resolved ,Nanowire ,Mode (statistics) ,Physics::Optics ,Bioengineering ,General Chemistry ,Substrate (electronics) ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Condensed Matter Physics ,Laser ,law.invention ,Condensed Matter::Materials Science ,Semiconductor ,law ,Optoelectronics ,General Materials Science ,Nanoscience & Nanotechnology ,business ,Lasing threshold ,QC - Abstract
© 2015 American Chemical Society. We experimentally determine the lasing mode(s) in optically pumped semiconductor nanowire lasers. The spatially resolved and angle-resolved far-field emission profiles of single InP nanowire lasers lying horizontally on a SiO2 substrate are characterized in a microphotoluminescence (μ-PL) setup. The experimentally obtained polarization dependent far-field profiles match very well with numerical simulations and enable unambiguous identification of the lasing mode(s). This technique can be applied to characterize lasing modes in other type of nanolasers that are integrated on a substrate in either vertical or horizontal configurations.
- Published
- 2015
27. Influence of Electrical Design on Core–Shell GaAs Nanowire Array Solar Cells
- Author
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Sudha Mokkapati, Zhe Li, Yesaya C. Wenas, Chennupati Jagadish, Hark Hoe Tan, and Lan Fu
- Subjects
Materials science ,Offset (computer science) ,business.industry ,Doping ,Nanowire ,Nanotechnology ,Carrier lifetime ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Condensed Matter Physics ,Nanowire array ,Electronic, Optical and Magnetic Materials ,Gallium arsenide ,Condensed Matter::Materials Science ,chemistry.chemical_compound ,Planar ,chemistry ,Condensed Matter::Superconductivity ,Optoelectronics ,Electrical design ,Electrical and Electronic Engineering ,business - Abstract
In this paper, we perform coupled optical and electrical simulation for core–shell junction GaAs nanowire array solar cells to obtain the important physical insights of how the cell efficiency is affected by various key parameters, including core–shell doping, junction position, carrier lifetime, and surface effect. Our study reveals that junction design in core–shell nanowires in terms of doping and geometry is largely restricted and affected by the small nanowire dimension, requiring different optimization from those of conventional planar solar cells. To take advantage of the radial p-n junction, high core and shell doping are essential to achieve effective radial carrier collection. Moreover, maintaining thin nanowire shell could effectively offset the detrimental surface effect for improved efficiency.
- Published
- 2015
28. An Order of Magnitude Increase in the Quantum Efficiency of (Al)GaAs Nanowires Using Hybrid Photonic–Plasmonic Modes
- Author
-
Dhruv Saxena, Li Li, Hark Hoe Tan, Sudha Mokkapati, Chennupati Jagadish, and Nian Jiang
- Subjects
Coupling ,Range (particle radiation) ,Materials science ,Fabrication ,business.industry ,Mechanical Engineering ,Nanowire ,Physics::Optics ,Bioengineering ,General Chemistry ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Condensed Matter Physics ,Condensed Matter::Materials Science ,Optoelectronics ,General Materials Science ,Quantum efficiency ,Photonics ,business ,Order of magnitude ,Plasmon - Abstract
We demonstrate 900% relative enhancement in the quantum efficiency (QE) of surface passivated GaAs nanowires by coupling them to resonant nanocavities that support hybrid photonic-plasmonic modes. This nonconventional approach to increase the QE of GaAs nanowires results in QE enhancement over the entire nanowire volume and is not limited to the near-field of the plasmonic structure. Our cavity design enables spatially and spectrally tunable resonant modes and efficient in- and out-coupling of light from the nanowires. Furthermore, this approach is not fabrication intensive; it is scalable and can be adapted to enhance the QE of a wide range of low QE semiconductor nanostructures.
- Published
- 2014
29. Large-scale statistics for threshold optimization of optically pumped nanowire lasers
- Author
-
Kun Peng, Sudha Mokkapati, Lan Fu, Dhruv Saxena, Xiaoyan Tang, Chennupati Jagadish, Juan Arturo Alanis, Nian Jiang, Patrick Parkinson, and Hark Hoe Tan
- Subjects
Photoluminescence ,Materials science ,Nanowire ,Physics::Optics ,Bioengineering ,02 engineering and technology ,Substrate (electronics) ,01 natural sciences ,law.invention ,Optics ,law ,0103 physical sciences ,General Materials Science ,QC ,QB ,010302 applied physics ,business.industry ,Mechanical Engineering ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Laser ,Characterization (materials science) ,Gain-switching ,Core (optical fiber) ,Optoelectronics ,0210 nano-technology ,business ,Lasing threshold - Abstract
Single nanowire lasers based on bottom-up III-V materials have been shown to exhibit room-temperature near-infrared lasing, making them highly promising for use as nanoscale, silicon-integrable and coherent light sources. While lasing behavior is reproducible, small variations in growth conditions across a substrate arising from the use of bottom-up growth techniques can introduce inter-wire disorder, either through geometric or material inhomogeneity. Nanolasers critically depend on both high material quality and tight dimensional tolerances, and as such, lasing threshold is both sensitive to, and a sensitive probe of such inhomogeneity. We present an all-optical characterization technique coupled to statistical analysis to correlate geometrical, and material parameters with lasing threshold. For these multiple-quantum-well nanolasers, it is found that low threshold is closely linked to longer lasing wavelength caused by losses in the core, providing a route to optimized future low-threshold devices. A best-in-group room temperature lasing threshold of 43 uJcm-2 under pulsed excitation was found, and overall device yields in excess of 50% are measured, demonstrating a promising future for the nanolaser architecture.
- Published
- 2017
30. Excited State Biexcitons in Atomically Thin MoSe2
- Author
-
Jin-Cheng Zheng, Xibin Wang, Jiajie Pei, Jiong Yang, Hark Hoe Tan, Qing-Hua Qin, Tie-Yu Lü, Sudha Mokkapati, Dragomir N. Neshev, Chennupati Jagadish, Yuerui Lu, and Fan Wang
- Subjects
Photon ,Binding energy ,General Physics and Astronomy ,02 engineering and technology ,010402 general chemistry ,7. Clean energy ,01 natural sciences ,General Materials Science ,Nanoscience & Nanotechnology ,Biexciton ,Condensed Matter::Quantum Gases ,Physics ,Condensed Matter::Other ,business.industry ,General Engineering ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Semiconductor ,Excited state ,Trion ,Atomic physics ,0210 nano-technology ,business ,Ground state ,Excitation - Abstract
© 2017 American Chemical Society. The tightly bound biexcitons found in atomically thin semiconductors have very promising applications for optoelectronic and quantum devices. However, there is a discrepancy between theory and experiment regarding the fundamental structure of these biexcitons. Therefore, the exploration of a biexciton formation mechanism by further experiments is of great importance. Here, we successfully triggered the emission of biexcitons in atomically thin MoSe2, via the engineering of three critical parameters: dielectric screening, density of trions, and excitation power. The observed binding energy and formation dynamics of these biexcitons strongly support the model that the biexciton consists of a charge attached to a trion (excited state biexciton) instead of four spatially symmetric particles (ground state biexciton). More importantly, we found that the excited state biexcitons not only can exist at cryogenic temperatures but also can be triggered at room temperature in a freestanding bilayer MoSe2. The demonstrated capability of biexciton engineering in atomically thin MoSe2 provides a route for exploring fundamental many-body interactions and enabling device applications, such as bright entangled photon sources operating at room temperature.
- Published
- 2017
31. Excited State Biexcitons in Atomically Thin MoSe
- Author
-
Jiajie, Pei, Jiong, Yang, Xibin, Wang, Fan, Wang, Sudha, Mokkapati, Tieyu, Lü, Jin-Cheng, Zheng, Qinghua, Qin, Dragomir, Neshev, Hark Hoe, Tan, Chennupati, Jagadish, and Yuerui, Lu
- Abstract
The tightly bound biexcitons found in atomically thin semiconductors have very promising applications for optoelectronic and quantum devices. However, there is a discrepancy between theory and experiment regarding the fundamental structure of these biexcitons. Therefore, the exploration of a biexciton formation mechanism by further experiments is of great importance. Here, we successfully triggered the emission of biexcitons in atomically thin MoSe
- Published
- 2017
32. Strong amplified spontaneous emission from high quality GaAs1−xSbx single quantum well nanowires
- Author
-
Hark Hoe Tan, Mark Lockrey, Sudha Mokkapati, Dhruv Saxena, Philippe Caroff, Fan Wang, Chennupati Jagadish, and Xiaoming Yuan
- Subjects
Amplified spontaneous emission ,Materials science ,Quantum point contact ,Nanowire ,Physics::Optics ,02 engineering and technology ,01 natural sciences ,Condensed Matter::Materials Science ,0103 physical sciences ,Physical and Theoretical Chemistry ,Quantum well ,QC ,010302 applied physics ,Condensed Matter::Other ,business.industry ,Quantum wire ,021001 nanoscience & nanotechnology ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,General Energy ,Quantum dot laser ,Quantum dot ,Optoelectronics ,Quantum efficiency ,0210 nano-technology ,business - Abstract
Quantum confinement in semiconductor nanowires is of contemporary interest. Enhancing the quantum efficiency of quantum wells in nanowires and minimizing intrinsic absorption are necessary for reducing the threshold of nanowire lasers and are promising for wavelength tunable emitters and detectors. Here, we report on growth and optimization of GaAs1–xSbx/Al1–yGayAs quantum well heterostructures formed radially around pure zinc blende GaAs core nanowires. The emitted photon energy from GaAs0.89Sb0.11 quantum well (1.371 eV) is smaller than the GaAs core, thus showing advantages over GaAs/Al1–yGayAs quantum well nanowires in photon emission. The high optical quality quantum well (internal quantum efficiency reaches as high as 90%) is carefully positioned so that the quantum well coincides with the maximum of the transverse electric (TE01) mode intensity profile. The obtained superior optical performance combined with the supported Fabry–Perot (F–P) cavity in the nanowire leads to the strong amplified spontaneous emission (ASE). Detailed studies of the amplified cavity mode are carried out by spatial–spectral photoluminescence (PL) imaging, where emission from nanowire is resolved both spatially and spectrally. Resonant emission is generated at nanowire ends and is polarized perpendicular to the nanowire, in agreement with the simulated polarization characteristics of the TE01 mode in the nanowire. The observation of strong ASE for single QW nanowire at room temperature shows the potential application of GaAs1–xSbx QW nanowires as low threshold infrared nanowire lasers.
- Published
- 2017
33. Single n
- Author
-
Kun, Peng, Patrick, Parkinson, Qian, Gao, Jessica L, Boland, Ziyuan, Li, Fan, Wang, Sudha, Mokkapati, Lan, Fu, Michael B, Johnston, Hark Hoe, Tan, and Chennupati, Jagadish
- Abstract
Developing single-nanowire terahertz (THz) electronics and employing them as sub-wavelength components for highly-integrated THz time-domain spectroscopy (THz-TDS) applications is a promising approach to achieve future low-cost, highly integrable and high-resolution THz tools, which are desirable in many areas spanning from security, industry, environmental monitoring and medical diagnostics to fundamental science. In this work, we present the design and growth of n
- Published
- 2017
34. Selective-Area Epitaxy of Pure Wurtzite InP Nanowires: High Quantum Efficiency and Room-Temperature Lasing
- Author
-
Li Li, Philippe Caroff, Qian Gao, Lan Fu, Chennupati Jagadish, Jennifer Wong-Leung, Hark Hoe Tan, Fan Wang, Sudha Mokkapati, Dhruv Saxena, and Yanan Guo
- Subjects
Quantum optics ,Materials science ,business.industry ,Mechanical Engineering ,Nanowire ,Physics::Optics ,Bioengineering ,General Chemistry ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Condensed Matter Physics ,Epitaxy ,Condensed Matter::Materials Science ,Selective area epitaxy ,Optoelectronics ,General Materials Science ,Quantum efficiency ,Nanoscience & Nanotechnology ,Photonics ,business ,Lasing threshold ,Wurtzite crystal structure - Abstract
© 2014 American Chemical Society. We report the growth of stacking-fault-free and taper-free wurtzite InP nanowires with diameters ranging from 80 to 600 nm using selective-area metal-organic vapor-phase epitaxy and experimentally determine a quantum efficiency of μ50%, which is on par with InP epilayers. We also demonstrate room-temperature, photonic mode lasing from these nanowires. Their excellent structural and optical quality opens up new possibilities for both fundamental quantum optics and optoelectronic devices.
- Published
- 2014
35. Guest Editorial: Selected Papers from Semiconductor and Integrated Optoelectronics (SIOE) 2018
- Author
-
Sudha Mokkapati
- Subjects
Engineering ,Semiconductor ,business.industry ,Nanotechnology ,Electrical and Electronic Engineering ,business ,Atomic and Molecular Physics, and Optics - Published
- 2019
36. (Invited) III-V Nanowires for Optoelectronic Applications
- Author
-
L. Fu, Chennupati Jagadish, Sudha Mokkapati, Qiang Gao, Nian Jiang, Hark Hoe Tan, Hannah J. Joyce, Yonghwan Lee, and Dhruv Saxena
- Subjects
Crystal ,Materials science ,law ,business.industry ,Nanowire ,Optoelectronics ,Laser ,business ,law.invention - Abstract
We present an overview of our work on improving the crystal quality and carrier lifetimes of our GaAs-based nanowires. These two properties are crucial for optoelectronic device applications and which we report by showing two examples of nanowire lasers and nanowire solar cells.
- Published
- 2013
37. Design Considerations for Semiconductor Nanowire-Plasmonic Nanoparticle Coupled Systems for High Quantum Efficiency Nanowires
- Author
-
Dhruv Saxena, Chennupati Jagadish, Hark Hoe Tan, and Sudha Mokkapati
- Subjects
Plasmonic nanoparticles ,Materials science ,Nanowires ,business.industry ,Nanowire ,Physics::Optics ,Nanoparticle ,Nanotechnology ,General Chemistry ,Surface Plasmon Resonance ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Surface plasmon polariton ,Biomaterials ,Condensed Matter::Materials Science ,Semiconductor ,Semiconductors ,Quantum Dots ,Optoelectronics ,General Materials Science ,Quantum efficiency ,Spontaneous emission ,business ,Plasmon ,Biotechnology - Abstract
The optimal geometries for reducing the radiative recombination lifetime and thus enhancing the quantum efficiency of III-V semiconductor nanowires by coupling them to plasmonic nanoparticles are established. The quantum efficiency enhancement factor due to coupling to plasmonic nanoparticles reduces as the initial quality of the nanowire increases. Significant quantum efficiency enhancement is observed for semiconductors only within about 15 nm from the nanoparticle. It is also identified that the modes responsible for resonant enhancement in the quantum efficiency of an emitter in the nanowire are geometric resonances of surface plasmon polariton modes supported at the nanowire/nanoparticle interface.
- Published
- 2013
38. Effect of Nanoparticle Size Distribution on the Performance of Plasmonic Thin-Film Solar Cells: Monodisperse Versus Multidisperse Arrays
- Author
-
Thomas Söderström, Sudha Mokkapati, Er-Chien Wang, Kylie R. Catchpole, and Sergey Varlamov
- Subjects
Materials science ,Nanophotonics ,Nanoparticle ,Nanotechnology ,Condensed Matter Physics ,Evaporation (deposition) ,Soft lithography ,Silver nanoparticle ,Electronic, Optical and Magnetic Materials ,Nanoimprint lithography ,law.invention ,Nanolithography ,law ,Particle size ,Electrical and Electronic Engineering - Abstract
The effect of the silver nanoparticle size distribution on the performance of plasmonic polycrystalline Si thin-film solar cells is studied. Monodisperse particle arrays are fabricated using nanoimprint lithography. Multidispersed particle arrays are fabricated using thermal evaporation followed by annealing. The short-circuit current enhancement for the cells without a back reflector is 24% and 18% with the multidisperse array and the monodispersed array, respectively. For the cells with a back reflector, the current enhancement increases to 34% and 30%, respectively, compared with 13% enhancement due to the reflector alone. Better performance of multidisperse Ag nanoparticle arrays is attributed to a broader scattering cross section of the array owing to a broad particle size distribution and a higher nanoparticle coverage.
- Published
- 2013
39. Polarization Tunable, Multicolor Emission from Core–Shell Photonic III–V Semiconductor Nanowires
- Author
-
Chennupati Jagadish, Sudha Mokkapati, Dhruv Saxena, Jennifer Wong-Leung, Patrick Parkinson, Nian Jiang, Qiang Gao, and Hark Hoe Tan
- Subjects
Plasmonic nanoparticles ,Materials science ,business.industry ,Mechanical Engineering ,Nanowire ,Physics::Optics ,Bioengineering ,Heterojunction ,Nanotechnology ,General Chemistry ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Condensed Matter Physics ,Polarization (waves) ,Condensed Matter::Materials Science ,Semiconductor ,Physics::Atomic and Molecular Clusters ,Optoelectronics ,General Materials Science ,Quantum efficiency ,Photonics ,business ,Plasmon - Abstract
We demonstrate luminescence from both the core and the shell of III-V semiconductor photonic nanowires by coupling them to plasmonic silver nanoparticles. This demonstration paves the way for increasing the quantum efficiency of large surface area nanowire light emitters. The relative emission intensity from the core and the shell is tuned by varying the polarization of the excitation source since their polarization response can be independently controlled. Independent control on emission wavelength and polarization dependence of emission from core-shell nanowire heterostructures opens up opportunities that have not yet been imagined for nanoscale polarization sensitive, wavelength-selective, or multicolor photonic devices based on single nanowires or nanowire arrays.
- Published
- 2012
40. Optically pumped room-temperature GaAs nanowire lasers
- Author
-
Patrick Parkinson, Qiang Gao, Chennupati Jagadish, Sudha Mokkapati, Hark Hoe Tan, Nian Jiang, and Dhruv Saxena
- Subjects
3D optical data storage ,Materials science ,business.industry ,Infrared ,Nanowire ,Context (language use) ,Laser ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Semiconductor laser theory ,law.invention ,Semiconductor ,law ,Optoelectronics ,business ,Lasing threshold - Abstract
Near-infrared lasers are important for optical data communication, spectroscopy and medical diagnosis. Semiconductor nanowires offer the possibility of reducing the footprint of devices for three-dimensional device integration and hence are being extensively studied in the context of optoelectronic devices. Although visible and ultraviolet nanowire lasers have been demonstrated widely, progress towards room-temperature infrared nanowire lasers has been limited because of material quality issues and Auger recombination. (Al)GaAs is an important material system for infrared lasers that is extensively used for conventional lasers. GaAs has a very large surface recombination velocity, which is a serious issue for nanowire devices because of their large surface-to-volume ratio. Here, we demonstrate room-temperature lasing in core-shell-cap GaAs/AlGaAs/GaAs nanowires by properly designing the Fabry-Pérot cavity, optimizing the material quality and minimizing surface recombination. Our demonstration is a major step towards incorporating (Al)GaAs nanowire lasers into the design of nanoscale optoelectronic devices operating at near-infrared wavelengths. © 2013 Macmillan Publishers Limited. All rights reserved.
- Published
- 2016
41. Enhanced minority carrier lifetimes in GaAs/AlGaAs core-shell nanowires through shell growth optimization
- Author
-
Jennifer Wong-Leung, Sudha Mokkapati, Joanne Etheridge, Qiang Gao, Patrick Parkinson, Hark Hoe Tan, Chennupati Jagadish, Changlin Zheng, Nian Jiang, and Steffen Breuer
- Subjects
Materials science ,business.industry ,Mechanical Engineering ,Analytical chemistry ,Shell (structure) ,Nanowire ,Bioengineering ,General Chemistry ,Chemical vapor deposition ,Carrier lifetime ,Condensed Matter Physics ,Dark field microscopy ,Scanning transmission electron microscopy ,Optoelectronics ,General Materials Science ,Metalorganic vapour phase epitaxy ,business ,Quantum tunnelling - Abstract
The effects of AlGaAs shell thickness and growth time on the minority carrier lifetime in the GaAs core of GaAs/AlGaAs core-shell nanowires grown by metal-organic chemical vapor deposition are investigated. The carrier lifetime increases with increasing AlGaAs shell thickness up to a certain value as a result of reducing tunneling probability of carriers through the AlGaAs shell, beyond which the carrier lifetime reduces due to the diffusion of Ga-Al and/or impurities across the GaAs/AlGaAs heterointerface. Interdiffusion at the heterointerface is observed directly using high-angle annular dark field scanning transmission electron microscopy. We achieve room temperature minority carrier lifetimes of 1.9 ns by optimizing the shell growth with the intention of reducing the effect of interdiffusion.
- Published
- 2016
42. Nanostructure photovoltaics based on III-V compound semiconductors
- Author
-
H. F. Lu, Patrick Parkinson, Sudha Mokkapati, Zhe Li, Chennupati Jagadish, Steffen Breuer, H.H. Tan, J. Lee, S. Turner, Greg Jolley, and Lan Fu
- Subjects
Materials science ,Nanostructure ,business.industry ,Photovoltaic system ,Nanowire ,Physics::Optics ,Nanotechnology ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Nanomaterials ,Condensed Matter::Materials Science ,Semiconductor ,Solar cell efficiency ,Photovoltaics ,Quantum dot ,Optoelectronics ,business - Abstract
In this work, solar cells based on III-V compound semiconductor quantum dots and nanowires are demonstrated. Experimental results based on material and device studies will be presented and discussed for high efficiency photovoltaic applications. © OSA 2013.
- Published
- 2016
43. Quantum dots and nanowires for photonics applications
- Author
-
Qiang Gao, H.H. Tan, Sudha Mokkapati, Hannah J. Joyce, Yong Kim, and Chennupati Jagadish
- Subjects
Materials science ,Photoluminescence ,business.industry ,Condensed Matter::Other ,Superlattice ,Nanowire ,Physics::Optics ,Heterojunction ,Chemical vapor deposition ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Gallium arsenide ,chemistry.chemical_compound ,Condensed Matter::Materials Science ,chemistry ,Quantum dot ,Optoelectronics ,Metalorganic vapour phase epitaxy ,business - Abstract
We review our results on integrated photonic devices fabricated using In GaAs quantum-dots. Selective-area metal organic chemical vapor deposition (MOCVD) is used to grow the active region with quantum dots emitting at different wavelengths for fabrication of the integrated devices. We will also review the structural and optical properties of III-V nanowires, and axial and radial nanowire heterostructures grown by MOCVD. In addition to binary nanowires, such as GaAs, In As, and InP, we have demonstrated ternary In GaAs and Alga as nanowires. Core-shell nanowires consisting of GaAs cores with Alga as shells, and core-multi shell nanowires with several alternating shells of Alga as and GaAs, exhibit strong photoluminescence. Axial segments of In GaAs have been incorporated within GaAs nanowires to form GaAs/In GaAs nanowire superlattices.
- Published
- 2016
44. Design and Room-Temperature Operation of GaAs/AlGaAs Multiple Quantum Well Nanowire Lasers
- Author
-
Xiaoming Yuan, Yanan Guo, Sudha Mokkapati, Hark Hoe Tan, Dhruv Saxena, Nian Jiang, and Chennupati Jagadish
- Subjects
Materials science ,Multiple quantum ,Nanowire ,Physics::Optics ,Bioengineering ,02 engineering and technology ,Fluence ,law.invention ,Condensed Matter::Materials Science ,020210 optoelectronics & photonics ,Optics ,law ,0202 electrical engineering, electronic engineering, information engineering ,General Materials Science ,QC ,business.industry ,Mechanical Engineering ,Heterojunction ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Polarization (waves) ,Laser ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Optoelectronics ,Coaxial ,0210 nano-technology ,business ,Lasing threshold - Abstract
We present the design and room-temperature lasing characteristics of single nanowires containing coaxial GaAs/AlGaAs multiple quantum well (MQW) active regions. The TE01 mode, which has a doughnut-shaped intensity profile and is polarized predominantly in-plane to the MQWs, is predicted to lase in these nanowire heterostructures and is thus chosen for the cavity design. Through gain and loss calculations, we determine the nanowire dimensions required to minimize loss for the TE01 mode and determine the optimal thickness and number of QWs for minimizing the threshold sheet carrier density. In particular, we show that there is a limit to the minimum and maximum number of QWs that are required for room-temperature lasing. Based on our design, we grew nanowires of a suitable diameter containing eight uniform coaxial GaAs/AlGaAs MQWs. Lasing was observed at room temperature from optically pumped single nanowires and was verified to be from TE01 mode by polarization measurements. The GaAs MQW nanowire lasers have a threshold fluence that is a factor of 2 lower than that previously demonstrated for room-temperature GaAs nanowire lasers.
- Published
- 2016
45. Doping-enhanced radiative efficiency enables lasing in unpassivated GaAs nanowires
- Author
-
Sudha Mokkapati, Chennupati Jagadish, Jeffrey A. Davis, Christopher R. Hall, Philippe Caroff, Yuda Wang, Lan Fu, Leigh M. Smith, Hark Hoe Tan, Tim Burgess, Zhe Li, and Dhruv Saxena
- Subjects
Materials science ,Passivation ,Differential gain ,Science ,Nanowire ,General Physics and Astronomy ,02 engineering and technology ,01 natural sciences ,Article ,General Biochemistry, Genetics and Molecular Biology ,0103 physical sciences ,010306 general physics ,QC ,Multidisciplinary ,business.industry ,General Chemistry ,Carrier lifetime ,021001 nanoscience & nanotechnology ,Semiconductor ,Optoelectronics ,Quantum efficiency ,Photonics ,0210 nano-technology ,business ,Lasing threshold - Abstract
Nanolasers hold promise for applications including integrated photonics, on-chip optical interconnects and optical sensing. Key to the realization of current cavity designs is the use of nanomaterials combining high gain with high radiative efficiency. Until now, efforts to enhance the performance of semiconductor nanomaterials have focused on reducing the rate of non-radiative recombination through improvements to material quality and complex passivation schemes. Here we employ controlled impurity doping to increase the rate of radiative recombination. This unique approach enables us to improve the radiative efficiency of unpassivated GaAs nanowires by a factor of several hundred times while also increasing differential gain and reducing the transparency carrier density. In this way, we demonstrate lasing from a nanomaterial that combines high radiative efficiency with a picosecond carrier lifetime ready for high speed applications., Until now, efforts to enhance the performance of nanolasers have focused on reducing the rate of non-radiative recombination. Here, Burgess et al. employ controlled impurity doping to increase the rate of radiative recombination.
- Published
- 2016
46. Semiconductor Nanowire Optoelectronic Devices
- Author
-
Chennupati Jagadish, Dhruv Saxena, Hark Hoe Tan, and Sudha Mokkapati
- Subjects
010302 applied physics ,Materials science ,business.industry ,Semiconductor materials ,Nanogenerator ,Nanowire ,Physics::Optics ,02 engineering and technology ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,021001 nanoscience & nanotechnology ,Laser ,01 natural sciences ,law.invention ,Condensed Matter::Materials Science ,Semiconductor ,law ,0103 physical sciences ,Optoelectronics ,Spontaneous emission ,0210 nano-technology ,business ,Nonlinear Sciences::Pattern Formation and Solitons ,Refractive index - Abstract
Semiconductor nanowires act as waveguides despite very small cross-section dimensions because of high refractive indices. The waveguiding properties of nanowires alter the way the semiconductor material interacts with light. We elaborate on the waveguiding properties of nanowires and the effect of these properties on the spontaneous emission characteristics of nanowires. The effect of waveguiding properties of nanowires on optoelectronic devices like nanowire solar cells and lasers is also discussed.
- Published
- 2016
47. Light trapping with titanium dioxide diffraction gratings fabricated by nanoimprinting
- Author
-
Thomas Söderström, Thomas P. White, Sudha Mokkapati, Er Chien Wang, Sergey Varlamov, and Kylie R. Catchpole
- Subjects
Photocurrent ,Materials science ,Silicon ,Renewable Energy, Sustainability and the Environment ,business.industry ,chemistry.chemical_element ,Condensed Matter Physics ,7. Clean energy ,Electronic, Optical and Magnetic Materials ,Nanoimprint lithography ,law.invention ,chemistry.chemical_compound ,Optics ,chemistry ,law ,Solar cell ,Titanium dioxide ,Optoelectronics ,Plasmonic solar cell ,Electrical and Electronic Engineering ,Thin film ,business ,Diffraction grating - Abstract
Dielectric scattering structures are a promising way of trapping light in solar cells. Titanium dioxide is a particularly attractive candidate material because of its high refractive index and ability to be deposited on a finished solar cell. Here, we present an experimental demonstration of photocurrent enhancement in thin film recrystallised silicon solar cells using TiO2 pillar arrays fabricated on the rear of the cells using nanoimprint lithography. A short circuit current enhancement of 19% is measured experimentally, and excellent agreement with numerical simulations is obtained. We show numerically that by replacing the Ag capping present on the cells with a detached rear Ag back reflector, the enhancement could reach 37%. Copyright © 2012 John Wiley & Sons, Ltd.
- Published
- 2012
48. Plasmonics and nanophotonics for photovoltaics
- Author
-
Er Chien Wang, Jaret Lee, Angelika Basch, Sudha Mokkapati, Arnold F. McKinley, Kylie R. Catchpole, and Fiona J. Beck
- Subjects
Nanostructure ,Materials science ,Geometrical optics ,business.industry ,Photovoltaic system ,Nanophotonics ,Physics::Optics ,Nanotechnology ,Condensed Matter Physics ,Photovoltaics ,General Materials Science ,Plasmonic solar cell ,Physical and Theoretical Chemistry ,business ,Diffraction grating ,Plasmon - Abstract
In recent years, there has been rapid development in the field of nanoscale light trapping for solar cells. This has been driven by the decrease in thickness of solar cells in order to reduce materials costs, as well as advances in fabrication technology and computer power for simulating nanoscale structures. Nanoscale light trapping offers the possibility of enhancing absorption beyond the limits achievable with geometrical optics for certain structures. It also allows the optical design to be separated from the electrical design, as for example in plasmonic solar cells. Most importantly, thin-film cell designs will need to incorporate nanophotonic light trapping in order to reach their ultimate efficiency limits. In this article, we review the major types of nanophotonic light trapping, including plasmonic, diffraction gratings, and random scattering surfaces and describe the major advantages and disadvantages of each. In addition, we describe the most important related fabrication and characterization technologies and provide an outlook on future directions in this field.
- Published
- 2011
49. Indium phosphide based solar cell using ultra-thin ZnO as an electron selective layer
- Author
-
Fiacre Rougieux, Sudha Mokkapati, Vidur Raj, Hark Hoe Tan, Mykhaylo Lysevych, Lan Fu, Kaushal Vora, Chennupati Jagadish, and Tâmara Sibele dos Santos
- Subjects
Materials science ,Acoustics and Ultrasonics ,Passivation ,02 engineering and technology ,Substrate (electronics) ,010402 general chemistry ,01 natural sciences ,law.invention ,chemistry.chemical_compound ,law ,Solar cell ,Homojunction ,Thin film ,business.industry ,Heterojunction ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry ,Indium phosphide ,Optoelectronics ,Quantum efficiency ,0210 nano-technology ,business - Abstract
According to the Shockley–Queisser limit, the maximum achievable efficiency for a single junction solar cell is ~33.2% which corresponds to a bandgap (E g) of 1.35 eV (InP). However, the maximum reported efficiency for InP solar cells remain at 24.2% ± 0.5%, that is >25% below the standard Shockley–Queisser limit. Through a wide range of simulations, we propose a new device structure, ITO/ ZnO/i-InP/p+ InP (p-i-ZnO-ITO) which might be able to fill this efficiency gap. Our simulation shows that the use of a thin ZnO layer improves passivation of the underlying i-InP layer and provides electron selectivity leading to significantly higher efficiency when compared to their n+/i/p+ homojunction counterpart. As a proof-of-concept, we fabricated ITO/ZnO/i-InP solar cell on a p+ InP substrate and achieved an open-circuit voltage (V oc) and efficiency as high as 819 mV and 18.12%, respectively, along with ~90% internal quantum efficiency. The entire device fabrication process consists of four simple steps which are highly controllable and reproducible. This work lays the foundation for a new generation of thin film InP solar cells based solely on carrier selective heterojunctions without the requirement of extrinsic doping and can be particularly useful when p- and n-doping are challenging as in the case of III–V nanostructures.
- Published
- 2018
50. Modal refractive index measurement in nanowire lasers—a correlative approach
- Author
-
Sudha Mokkapati, Juan Arturo Alanis, Lan Fu, Hark Hoe Tan, Chennupati Jagadish, Patrick Parkinson, Kun Peng, Dhruv Saxena, and Nian Jiang
- Subjects
Materials science ,Biomedical Engineering ,Nanowire ,Physics::Optics ,Bioengineering ,02 engineering and technology ,Electron ,Multimodal characterisation ,01 natural sciences ,law.invention ,law ,0103 physical sciences ,General Materials Science ,Electrical and Electronic Engineering ,Spectroscopy ,III-V Nanowire lasers ,010302 applied physics ,business.industry ,Nanolaser ,General Chemistry ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,021001 nanoscience & nanotechnology ,Laser ,Atomic and Molecular Physics, and Optics ,Modal ,Optoelectronics ,0210 nano-technology ,business ,Refractive index ,Lasing threshold - Abstract
We present a method to correlate multimodal measurements—namely optical spectroscopy and electron microscopy—over large ensembles of randomly distributed single nano-objects. Using an algorithmic approach derived from astrometry, a marker-free method of uniquely associating nano-objects characterised using multiple techniques is described. This approach is applied to nanolasers, enabling an experimental calculation of modal refractive index in sub-micron diameter nanowires. By matching the lasing spectrum and electron microscopy image of 13 nanowire lasers, the refractive index of the TE01 mode in GaAs/AlGaAs multiple-quantum well nanolasers is determined to be n g = 4.7 ± 0.3.
- Published
- 2018
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