17 results on '"John Jarman"'
Search Results
2. Combined SEM-CL and STEM investigation of green InGaN quantum wells
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Rachel A. Oliver, Menno J. Kappers, Boning Ding, John Jarman, Ding, B [0000-0003-2868-3416], Apollo - University of Cambridge Repository, Ding, Boning [0000-0003-2868-3416], Jarman, John [0000-0001-8095-8603], and Oliver, Rachel [0000-0003-0029-3993]
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Paper ,Materials science ,Acoustics and Ultrasonics ,Semiconductors and photonics ,business.industry ,Atomic force microscopy ,quantum well ,green LEDs ,Cathodoluminescence ,Gallium nitride ,cathodoluminescence ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,chemistry ,TEM ,Optoelectronics ,AFM ,business ,gallium nitride ,Quantum well - Abstract
The microstructure of green-emitting InGaN/GaN quantum well (QW) samples grown at different temperatures was studied using cross-section scanning transmission electron microscopy (STEM) and plan-view cathodoluminescence (CL). The sample with the lowest InGaN growth temperature exhibits microscale variations in the CL intensity across the sample surface. Using STEM analysis of such areas, the observed darker patches do not correspond to any observable extended defect. Instead, they are related to changes in the extent of gross-well width fluctuations in the QWs, with more brightly emitting regions exhibiting a high density of such fluctuations, whilst dimmer regions were seen to have InGaN QWs with a more uniform thickness.
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- 2022
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3. Study of Ti contacts to corundum α -Ga 2 O 3
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Rachel A. Oliver, Fabien Massabuau, D Nicol, Paul R. Chalker, András Kovács, John Jarman, F Adams, J.W. Roberts, Massabuau, F [0000-0003-1008-1652], and Apollo - University of Cambridge Repository
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Paper ,Acoustics and Ultrasonics ,corundum ,Annealing (metallurgy) ,oxidation ,Corundum ,02 engineering and technology ,engineering.material ,Conductivity ,01 natural sciences ,metal contact ,gallium oxide ,0103 physical sciences ,ddc:530 ,Ohmic contact ,QC ,Emerging Leaders 2021 ,010302 applied physics ,diffusion ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Chemical engineering ,Transmission electron microscopy ,engineering ,Grain boundary ,annealing ,Crystallite ,0210 nano-technology ,Layer (electronics) - Abstract
We present a study of the electrical, structural and chemical properties of Ti contacts on atomic layer deposited α-Ga2O3 film. Ti forms an ohmic contact with α-Ga2O3. The contact performance is highly dependent on the post-evaporation annealing temperature, where an improved conductivity is obtained when annealing at 450 °C, and a strong degradation when annealing at higher temperatures. Structural and chemical characterisation by transmission electron microscopy techniques reveal that the electrical improvement or degradation of the contact upon annealing can be attributed to oxidation of the Ti metallic layer by the Ga2O3 film in combination with the possibility for Ti diffusion into the Au layer. The results highlight that the grain boundaries and inclusions in the Ga2O3 film provide fast diffusion pathways for this reaction, leaving the α-Ga2O3 crystallites relatively unaffected—this result differs from previous reports conducted on β-Ga2O3. This study underlines the necessity for a phase-specific and growth method-specific study of contacts on Ga2O3 devices.
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- 2021
4. Pure single photon emission from an InGaN/GaN quantum dot
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Mark J. Holmes, Yasuhiko Arakawa, Tongtong Zhu, Rachel A. Oliver, Fc-P Massabuau, and John Jarman
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010302 applied physics ,Materials science ,business.industry ,General Engineering ,02 engineering and technology ,Quantum key distribution ,021001 nanoscience & nanotechnology ,01 natural sciences ,Single photon emission ,Quantum technology ,Quantum dot ,0103 physical sciences ,Optoelectronics ,High Energy Physics::Experiment ,General Materials Science ,Photonics ,0210 nano-technology ,business ,Excitation ,QC - Abstract
Single-photon emitters with high degrees of purity are required for photonic-based quantum technologies. InGaN/GaN quantum dots are promising candidates for the development of single-photon emitters but have typically exhibited emission with insufficient purity. Here, pulsed single-photon emission with high purity is measured from an InGaN quantum dot. A raw g(2)(0) value of 0.043 ± 0.009 with no corrections whatsoever is achieved under quasi-resonant pulsed excitation. Such a low value is, in principle, sufficient for use in quantum key distribution systems.
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- 2021
5. An oral bacterial cocktail for kidney protection
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Dylan Dodd and John Jarman
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Kidney ,business.industry ,Nitrogen ,Biomedical Engineering ,Medicine (miscellaneous) ,Renal function ,Bioengineering ,Pharmacology ,medicine.disease ,Computer Science Applications ,medicine.anatomical_structure ,Models, Animal ,Medicine ,Animals ,Renal Insufficiency ,business ,Biotechnology ,Kidney disease - Abstract
The oral delivery of a microencapsulated bacterial cocktail into animal models of kidney disease promotes the degradation of nitrogenous waste in the gut, thereby supporting renal function.
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- 2020
6. On-Chip Thermal Insulation Using Porous GaN
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Florin Udrea, John Jarman, Andrea De Luca, Tongtong Zhu, Rachel A. Oliver, Peter Griffin, Bogdan F. Spiridon, and Yingjun Liu
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Materials science ,porous ,business.industry ,lcsh:A ,Gallium nitride ,Conductivity ,Chip ,GaN ,chemistry.chemical_compound ,Thermal conductivity ,chemistry ,Thermal insulation ,Thermal ,thermal insulation ,3-omega ,Optoelectronics ,thermal conductivity ,lcsh:General Works ,gallium nitride ,Porosity ,business ,Order of magnitude - Abstract
This study focuses on the thermal characterization of porous gallium nitride (GaN) usingan extended 3ω method. Porous semiconductor materials provide a solution to the need for on-chipthermal insulation, a fundamental requirement for low-power, high-speed and high-accuracythermal sensors. Thermal insulation is especially important in GaN devices, due to the intrinsicallyhigh thermal conductivity of the material. The results show one order of magnitude reduction inthermal conductivity, from 130 W/mK to 10 W/mK, in line with theoretical predictions for porousmaterials. This achievement is encouraging in the quest for integrating sensors with opto-, powerandRF-electronics on a single GaN chip.
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- 2018
7. Nitride Single Photon Sources
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Robert A. Taylor, Tongtong Zhu, Fengzai Tang, Stefan Schulz, Saroj Kanta Patra, Tim J. Puchtler, Claudius Kocher, Rachel A. Oliver, Benjamin P. L. Reid, John Jarman, Tong Wang, and Christopher X. Ren
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Quantum communications ,Quantum key distribution paradigms ,Photon ,Physics::Optics ,Nitride single photon sources ,Quantum channel ,Quantum light sources ,Quantum key distribution ,5108 Quantum Physics ,Nitride quantum dots ,4009 Electronics, Sensors and Digital Hardware ,5102 Atomic, Molecular and Optical Physics ,Epitaxial growth ,40 Engineering ,Quantum computer ,Physics ,Nitride materials system ,InGaN ,Quantum dots ,business.industry ,TheoryofComputation_GENERAL ,Optical polarization ,Engineering physics ,Single photon emission ,Nanostructures ,Quantum technology ,Photonics ,Quantum dot ,ComputerSystemsOrganization_MISCELLANEOUS ,Stimulated emission ,business ,51 Physical Sciences - Abstract
Single photon sources are a key enabling technology for quantum communications, and in the future more advanced quantum light sources may underpin other quantum information processing paradigms such as linear optical quantum computation. In considering possible practical implementations of future quantum technologies, the nitride materials system is attractive since nitride quantum dots (QDs) achieve single photon emission at easily accessible temperatures [1], potentially enabling the implementation of quantum key distribution paradigms in contexts where cryogenic cooling is impracticable.
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- 2018
8. alpha-Ga2O3 grown by low temperature atomic layer deposition on sapphire
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Paul A. Midgley, John Jarman, Paul R. Chalker, F.C-P. Massabuau, Rachel A. Oliver, Duncan N. Johnstone, and J.W. Roberts
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010302 applied physics ,Scanning electron microscope ,Band gap ,Analytical chemistry ,Oxides ,02 engineering and technology ,Substrate (electronics) ,Atomic layer epitaxy ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,X-ray diffraction ,Amorphous solid ,Inorganic Chemistry ,Atomic layer deposition ,Phase (matter) ,0103 physical sciences ,Materials Chemistry ,Sapphire ,Semiconducting gallium compounds ,0210 nano-technology ,Scanning electron diffraction ,QC - Abstract
α-Ga2O3 is a metastable phase of Ga2O3 of interest for wide bandgap engineering since it is isostructural with α-In2O3 and α-Al2O3. α-Ga2O3 is generally synthesised under high pressure (several GPa) or relatively high temperature (∼500 °C). In this study, we report the growth of α-Ga2O3 by low temperature atomic layer deposition (ALD) on sapphire substrate. The film was grown at a rate of 0.48 A/cycle, and predominantly consists of α-Ga2O3 in the form of ( 0001 ) -oriented columns originating from the interface with the substrate. Some inclusions were also present, typically at the tips of the α phase columns and most likely comprising e-Ga2O3. The remainder of the Ga2O3 film – i.e. nearer the surface and between the α-Ga2O3 columns, was amorphous. The film was found to be highly resistive, as is expected for undoped material. This study demonstrates that α-Ga2O3 films can be grown by low temperature ALD and suggests the possibility of a new range of ultraviolet optoelectronic and power devices grown by ALD. The study also shows that scanning electron diffraction is a powerful technique to identify the different polymorphs of Ga2O3 present in multiphase samples.
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- 2018
9. Highly polarized electrically driven single-photon emission from a non-polar InGaN quantum dot
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Robert A. Taylor, Tong Wang, Tim J. Puchtler, Rachel A. Oliver, John Jarman, Claudius Kocher, Tongtong Zhu, Luke P. Nuttall, Jarman, John [0000-0001-8095-8603], Zhu, Tongtong [0000-0002-9481-8203], Oliver, Rachel [0000-0003-0029-3993], and Apollo - University of Cambridge Repository
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010302 applied physics ,Materials science ,Photon ,Physics and Astronomy (miscellaneous) ,business.industry ,Oscillator strength ,Wide-bandgap semiconductor ,02 engineering and technology ,Electroluminescence ,021001 nanoscience & nanotechnology ,01 natural sciences ,5108 Quantum Physics ,Crystal ,Quantum dot ,0103 physical sciences ,Optoelectronics ,Degree of polarization ,0210 nano-technology ,business ,51 Physical Sciences ,Excitation ,40 Engineering - Abstract
© 2017 Author(s). Nitride quantum dots are well suited for the deterministic generation of single photons at high temperatures. However, this material system faces the challenge of large in-built fields, decreasing the oscillator strength and possible emission rates considerably. One solution is to grow quantum dots on a non-polar plane; this gives the additional advantage of strongly polarized emission along one crystal direction. This is highly desirable for future device applications, as is electrical excitation. Here, we report on electroluminescence from non-polar InGaN quantum dots. The emission from one of these quantum dots is studied in detail and found to be highly polarized with a degree of polarization of 0.94. Single-photon emission is achieved under excitation with a constant current giving a g(2)(0) correlation value of 0.18. The quantum dot electroluminescence persists up to temperatures as high as 130 K.
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- 2018
10. Atomic layer deposited α-Ga2O3 solar-blind photodetectors
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James Moloney, Fabien Massabuau, Paul R. Chalker, Jirayut Brister, Oliver Tesh, Lana Lee, J.W. Roberts, Serge Karboyan, Martin Kuball, Rachel A. Oliver, Tahmida N. Huq, John Jarman, and Manikant Singh
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010302 applied physics ,Argon ,Acoustics and Ultrasonics ,Hydrogen ,Annealing (metallurgy) ,Analytical chemistry ,chemistry.chemical_element ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Microstructure ,01 natural sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Atomic layer deposition ,Responsivity ,chemistry ,Impurity ,0103 physical sciences ,0210 nano-technology ,Forming gas ,QC - Abstract
Low temperature atomic layer deposition was used to deposit α-Ga2O3 films, which were subsequently annealed at various temperatures and atmospheres. The α-Ga2O3 phase is stable up to 400 °C, which is also the temperature that yields the most intense and sharpest reflection by x-ray diffraction. Upon annealing at 450 °C and above, the material gradually turns into the more thermodynamically stable ε or β phase. The suitability of the materials for solar-blind photodetector applications has been demonstrated with the best responsivity achieved being 1.2 A W−1 under 240 nm illumination and 10 V bias, for the sample annealed at 400 °C in argon. It is worth noting however that the device performance strongly depends on the annealing conditions, with the device annealed in forming gas behaving poorly. Given that the tested devices have similar microstructure, the discrepancies in device performance are attributed to hydrogen impurities.
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- 2019
11. Solubility Part 2: Colorimetry
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Ratna Tantra, D. Gohil, Kenneth N. Robinson, and John Jarman
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Materials science ,Environmental chemistry ,Inorganic chemistry ,Solubility ,Colorimetry (chemical method) - Published
- 2016
12. Suitability of analytical methods to measure solubility for the purpose of nanoregulation
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John Jarman, Calin David, Carlos Rey-Castro, Meike van der Zande, Ratna Tantra, Kenneth N. Robinson, Julie Laloy, Eduardo Bolea, Francisco Laborda, Anna K. Undas, Hans Bouwmeester, and Jean-Michel Dogné
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Novel Foods & Agrochains ,BU Toxicologie ,Biomedical Engineering ,Data reliability ,Nanotechnology ,02 engineering and technology ,Atomic spectroscopy ,010501 environmental sciences ,Toxicology ,Novel Foods & Agroketens ,01 natural sciences ,Chemistry Techniques, Analytical ,BU Toxicology, Novel Foods & Agrochains ,Solubility ,0105 earth and related environmental sciences ,VLAG ,Nanomaterials ,Measure (data warehouse) ,Chemistry ,Spectrophotometry, Atomic ,solubility ,BU Toxicology ,Analytic Sample Preparation Methods ,Reproducibility of Results ,regulation ,Electrochemical Techniques ,Models, Theoretical ,021001 nanoscience & nanotechnology ,Nanostructures ,BU Toxicologie, Novel Foods & Agroketens ,Colorimetry ,Biochemical engineering ,0210 nano-technology ,Regulation - Abstract
Solubility is an important physicochemical parameter in nanoregulation. If nanomaterial is completely soluble, then from a risk assessment point of view, its disposal can be treated much in the same way as “ordinary” chemicals, which will simplify testing and characterisation regimes. This review assesses potential techniques for the measurement of nanomaterial solubility and evaluates the performance against a set of analytical criteria (based on satisfying the requirements as governed by the cosmetic regulation as well as the need to quantify the concentration of free (hydrated) ions). Our findings show that no universal method exists. A complementary approach is thus recommended, to comprise an atomic spectrometry-based method in conjunction with an electrochemical (or colorimetric) method. This article shows that although some techniques are more commonly used than others, a huge research gap remains, related with the need to ensure data reliability. We acknowledge support from European Union Seventh Framework Programme (FP7-NMP.2012.1.3-3) under grant agreement no. 310584 (NANoREG). This work was supported by the Service Public de Wallonie (SPW) – Direction ge´ne´rale ope´rationnelle – Economie, Emploi et Recherche (DGO6), De´partement des Programmes de Recherche (NANoREG, SPW/UNamur research convention N 1317938).
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- 2016
13. Improvement of single photon emission from InGaN QDs embedded in porous micropillars
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Yasuhiko Arakawa, Helen Springbett, Rachel A. Oliver, Mark J. Holmes, John Jarman, Tongtong Zhu, Jarman, John [0000-0001-8095-8603], Zhu, Tongtong [0000-0002-9481-8203], Oliver, Rachel [0000-0003-0029-3993], and Apollo - University of Cambridge Repository
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Photon ,Materials science ,Physics and Astronomy (miscellaneous) ,business.industry ,Autocorrelation ,Physics::Optics ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Laser ,01 natural sciences ,law.invention ,Wavelength ,law ,Quantum dot ,Excited state ,0103 physical sciences ,Optoelectronics ,010306 general physics ,0210 nano-technology ,business ,Porosity ,Mesoporous material - Abstract
In many InGaN/GaN single photon emitting structures, significant contamination of the single photon stream by background emission is observed. Here, utilizing InGaN/GaN quantum dots incorporated in mesoporous distributed Bragg reflectors (DBRs) within micropillars, we demonstrate methods for the reduction of this contamination. Using the resulting devices, autocorrelation measurements were performed using a Hanbury Brown and Twiss set-up, and thus, we report a working quantum dot device in the III-nitride system utilizing mesoporous DBRs. Uncorrected g(2)(0) autocorrelation values are shown to be significantly improved when excited with a laser at longer wavelengths and lower powers. Through this optimization, we report a g(2)(0) value from a blue-emitting InGaN/GaN quantum dot of 0.126 ± 0.003 without any form of background correction.
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- 2018
14. Role of standard documents in advancing the standardization of microfluidics connectors
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John Jarman, Henne van Heeren, and Ratna Tantra
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Background information ,Process management ,Standardization ,business.industry ,Computer science ,Mechanical Engineering ,010401 analytical chemistry ,Interoperability ,Microfluidics ,Nanotechnology ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Product engineering ,Atomic and Molecular Physics, and Optics ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,Action (philosophy) ,Order (exchange) ,Electrical and Electronic Engineering ,0210 nano-technology ,business ,Publication - Abstract
An emerging trend within the microfluidic community is to standardize common parts in order to facilitate design and production activities. The goal is clear: to enhance interoperability and promote plug-and-play. A recent launch of a pan-European project, Microfluidic (MF) Manufacturing, has identified an item that is in immediate need of standardization: having in place geometrical specifications for MF connectors. In order to accelerate the adoption of such standards, there is a need to consider the pivotal role of standard documents. The purpose of this paper is to provide background information on document standards development. In addition, the future implications related to the MF manufacturing project will be discussed. A strengths, weaknesses, opportunities, and threats analysis has been carried out to identify points of action. The findings show that although there is a need to publish under International Organization for Standardization (ISO), the actual realization of a full ISO standard document is not feasible. The recommendation is to initially publish via an ISO Workshop Agreement. Parallel to such activity, there is a need to encourage stakeholders help kick start a currently dormant working group that supports microfluidics under ISO to help pave the way for future standardization activities in the microfluidics community.
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- 2016
15. μTAS (micro total analysis systems) for the high-throughput measurement of nanomaterial solubility
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John Jarman and Ratna Tantra
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History ,Materials science ,Oxide ,chemistry.chemical_element ,Nanotechnology ,Zinc ,Conductivity ,Computer Science Applications ,Education ,Nanomaterials ,chemistry.chemical_compound ,Capillary electrophoresis ,chemistry ,Solubility ,Throughput (business) ,Dissolution - Abstract
There is a consensus in the nanoecotoxicology community that better analytical tools i.e. faster and more accurate ones, are needed for the physicochemical characterisation of nanomaterials in environmentally/biologically relevant media. In this study, we introduce the concept of μTAS (Micro Total Analysis Systems), which was a term coined to encapsulate the integration of laboratory processes on a single microchip. Our focus here is on the use of a capillary electrophoresis (CE) with conductivity detection microchip and how this may be used for the measurement of dissolution of metal oxide nanomaterials. Our preliminary results clearly show promise in that the device is able to: a) measure ionic zinc in various ecotox media with high selectivity b) track the dynamic dissolution events of zinc oxide (ZnO) nanomaterial when dispersed in fish medium.
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- 2013
16. Adsorptive Capacity of Wood Charcoal for Dissolved Substances in Relation to the Temperature of Carbonization
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J. C. Philip and John Jarman
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Chemistry ,Carbonization ,visual_art ,Environmental chemistry ,General Engineering ,visual_art.visual_art_medium ,Organic chemistry ,Physical and Theoretical Chemistry ,Charcoal - Published
- 1924
17. Progress in atomic layer deposited [alpha]-Ga2O3 materials and solar-blind detectors
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G L. Dallas, Daniel A. Hunter, J.W. Roberts, M McLelland, E A. Nicolson, Robert W. Martin, Paul R. Chalker, András Kovács, Fabien Massabuau, Paul R. Edwards, D Nicol, John Jarman, Rachel A. Oliver, Teherani, Ferechteh H., Look, David C., Rogers, David J., Jarman, John [0000-0001-8095-8603], Oliver, Rachel [0000-0003-0029-3993], and Apollo - University of Cambridge Repository
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010302 applied physics ,Materials science ,business.industry ,Band gap ,Photoconductivity ,02 engineering and technology ,Photodetection ,021001 nanoscience & nanotechnology ,Epitaxy ,01 natural sciences ,7. Clean energy ,Atomic layer deposition ,QC350 ,Semiconductor ,0103 physical sciences ,Optoelectronics ,ddc:610 ,0210 nano-technology ,business ,Luminescence ,Layer (electronics) - Abstract
Atomic layer deposition (ALD) offers a low thermal budget method for producing α-Ga2O3 films on sapphire substrate. In this paper we review the recent progress on plasma-enhanced ALD growth of α-Ga2O3 and present the optical and photoconductive properties of the deposited films. We show that the deposited material exhibits an epitaxial relationship with the sapphire substrate, and with an atomically sharp film-substrate interface. The α-Ga2O3 films had an optical bandgap energy measured at 5.11 eV, and exhibited a broad luminescence spectrum dominated by ultraviolet, blue and green bands, in line with current literature. We finally demonstrate the suitability of the material for solar-blind photodetection.
- Full Text
- View/download PDF
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