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The intrinsic non‐Hermiticity of photonic devices with tunable optical gain and loss makes them excellent platforms to explore and implement applications based on parity‐time symmetry, and a notable example is mode management in micro‐cavity lasers. Thus far, parity‐time‐symmetric lasers are fabricated via conventional top‐down etching processes, which are known to cause cavity sidewall roughness that is potentially detrimental to laser performance. Bottom‐up fabrication of parity‐time‐symmetric lasers, however, has seen limited success due to strict requirements on the uniformity of cavity morphology. Here, parity‐time‐symmetric lasing is demonstrated in coupled InP micro‐ring cavities grown directly by selective area epitaxy. With a facet engineering technique, ring laser cavities with a highly deterministic morphology are realized, enabling parity‐time‐symmetric laser designs. Furthermore, benefiting from the versatility and controllability of this bottom‐up process, lasing mode selectivity can be enhanced through coupling gap tuning and cavity shape engineering, leading to single‐mode lasing with a peak side mode suppression ratio exceeding 17 dB and a threefold single‐mode brightness enhancement compared to a single, uncoupled laser cavity. This work unlocks a lasing mode management strategy that is previously unavailable to bottom‐up laser cavities, which is a major step toward the realization of on‐chip, low‐loss, and single‐mode micro‐cavity lasers. [ABSTRACT FROM AUTHOR]

Extending the emission wavelength of III‐V nanowire (NW) lasers grown on silicon into the mid‐infrared (MIR) spectral range has strong potential for applications. Examples include optical sensing and metrology, as well as integrated silicon photonics for information technologies. NW‐lasers with continuous wave (CW) operation, have remained, however, scarce in the MIR due to significant material physics challenges, and intrinsic effects such as Auger recombination that limit the radiative efficiency. Here, the CW operation of single InAs NW‐lasers site‐selectively grown on Si with emission in the range of 2.4–2.7 µm is reported. The cavity design is optimized via simulations of the threshold material gain and the parameters for selective area growth to minimize the modal gain for the TE01 optical mode. For NW diameters exceeding 700 nm, lasing under CW optical pumping with low thresholds of 1.4–27 kW cm−2 are obtained from 10 to 90 K for NW lengths ranging from 9–30 µm. The observed lasing behavior is quantified by the observation of clear positive net modal gain (630 cm−1) obtained using Hakki‐Paoli analysis. These findings mark an important advancement in the development of nanolasers for integrated MIR photonics. [ABSTRACT FROM AUTHOR]

CMOS‐compatible III–V semiconductor nanowire infrared photodetectors have attracted extensive research interest in various fields such as Si photonics and gas sensors. However, the traditional vertical configuration of nanowires limits their applications at the circuit level. Here, an in‐plane selective area epitaxy route is developed to grow large‐scale InAsSb nanowire networks on patterned Si substrates. By precisely tuning the growth parameters, the well‐aligned InAsSb nanowire networks with good selectivity are successfully achieved. Detailed structural studies confirm that there is a sharp interface between the InAsSb nanowire and the substrate. On the basis of optoelectronic measurements, it is confirmed that the fabricated InAsSb nanowire network photodetectors exhibit a low dark current density (≤2 mA cm−2) and a wide spectral response (1200–1650 nm) at room temperature, covering the important telecommunication bands. Moreover, these devices present a high on‐off ratio, large responsivity, high detectivity, and rapid response speed at zero bias voltage. At the illumination wavelength of 1200 nm, the on‐off ratio, responsivity, detectivity, and response time of a double nanowire networks photodetector can reach 2680, 286.9 mA W−1, 1.4 × 1010 Jones and 75.3 µs, respectively. This work offers a straightforward approach to in situ fabricating high‐performance scalable nanowire photodetectors. [ABSTRACT FROM AUTHOR]

Experiments on the growth of self-assembled InP/GaInP2 quantum dots in dielectric mask 0.1–1 μm apertures by MOVPE epitaxy have been carried out. A sequence of operations for the implementation of the lift-off lithography method is proposed and implemented. The possibility of obtaining apertures with 100 nm diameter and less is shown. Combination of thermally deposited SiO2 and wet etching is shown to produce minimal amount of nonradiative defects and results in a stable PL signal from single QDs in the aperture. [ABSTRACT FROM AUTHOR]

Semiconductor nanowires (NWs) in horizontal configuration could provide a path for scalable NW-based devices. Bottom–up large-scale manufacturing of these nanostructures by selective area epitaxy (SAE) relies on precise nanopatterning of various shapes on the growth masks. Electron beam lithography offers an extraordinary accuracy suited for the purpose. However, this technique is not economically viable for large production as it has a low throughput and requires high investment and operational costs. Nanoimprint lithography (NIL) has the potential to reduce fabrication time and costs significantly while requiring less sophisticated equipment. In this work, we utilize both thermal and UV NIL for patterning substrates for SAE, elucidating the advantages and disadvantages of each lithography technique. We demonstrate the epitaxial growth of Ge and GaAs NWs on these substrates, where we observe high-quality mono-crystalline structures. Even though both processes can produce small uniform structures suitable for SAE, our results show that UV NIL proves to be superior and enables reliable and efficient patterning of sub-100 nm mask features at the wafer scale. [ABSTRACT FROM AUTHOR]

We employed the selective-area-epitaxy technique using metalorganic chemical vapor deposition to fabricate and study samples of semiconductor heterostructures that incorporate highly strained InGaAs quantum wells (980–990 nm emission wavelength). Selective area epitaxy of InGaAs quantum wells was performed on templates that had a patterned periodic structure consisting of a window (where epitaxial growth occurred) and a passive mask (where epitaxial growth was suppressed), each with a width of 100 µm for every element. Additionally, a selectively grown potential barrier layer was included, which was characterized by an almost parabolic curvature profile of the surface. We conducted a study on the influence of the curvature profile of the growth surface on the optical properties of InGaAs quantum wells and the spatial distribution of composition in an ultrawide window. Our results showed that, under fixed selective-area-epitaxy conditions, the composition of the InxGa1−xAs and the wavelength of the quantum-well emission changed across the width of the window. Our study demonstrates that increasing the curvature profile of the growth surface of highly strained quantum wells leads to a transition in the photoluminescence wavelength distribution profile across the window, from quasi-parabolic to inverted parabolic. [ABSTRACT FROM AUTHOR]

AlzGa1−zAs layers of various compositions were grown using metalorganic chemical vapor deposition on a GaAs substrate with a pattern of alternating SiO2 mask/window stripes, each 100 µm wide. Microphotoluminescence maps and thickness profiles of AlzGa1−zAs layers that demonstrated the distribution of the growth rate and z in the window were experimentally studied. It was shown that the layer growth rate and the AlAs mole fraction increased continuously from the center to the edge of the window. It was experimentally shown that for a fixed growth time of 10 min, as z increased from 0 to 0.3, the layer thickness difference between the center of the window and the edge increased from 700 Å to 1100 Å, and the maximum change in z between the center of the window and the edge reached Δz 0.016, respectively. Within the framework of the vapor -phase diffusion model, simulations of the spatial distribution of the layer thickness and z across the window were carried out. It was shown that the simulation results were in good agreement with the experimental results for the effective diffusion length D/k: Ga—85 µm, Al—50 µm. [ABSTRACT FROM AUTHOR]

Photonic crystals can be used to achieve high‐performance surface‐emitting lasers and enable novel photonic topological insulator devices. In this work, a GaAs/InGaAs heterojunction nanowire platform by selective area metalorganic vapor phase epitaxy for such applications is demonstrated. The nanowires are arranged into deformed honeycomb lattices on silicon‐on‐insulator substrate to exploit the quadrupolar photonic band‐edge mode. Core–shell and axial heterostructures are formed with their crystalline properties studied by scanning transmission electron microscopy. Room‐temperature, single mode lasing from both stretched and compressed honeycomb lattices within the telecom‐O band, with lasing threshold as low as 1.25 µJ cm−2 is demonstrated. The potential of using InGaAs nanowire‐based honeycomb lattices for small‐divergence surface‐emitting lasers and topological edge mode lasers is investigated. Finite‐difference time‐domain far field simulations suggest a sub‐10° beam divergence can be achieved thanks to the out‐of‐plane diffraction. [ABSTRACT FROM AUTHOR]

The realization of on‐chip microlasers with out‐of‐plane, controllable emission direction has been one of the core research themes in modern photonics. Traditional approaches for directional light scattering, including plasmonic nanoantennas and passive dielectric metasurfaces, are not suitable for on‐chip integration due to potential metallic contamination and reliance on external light sources. Meanwhile, achieving directional emission in active III–V microcavity lasers remains challenging due to geometrical symmetry and large free‐space coupling losses. Here, a novel approach is presented to realize directional lasing in an all‐dielectric, bottom‐up grown material system by coupling the laser emission from an InP microring cavity into a vertical nanowire at the ring center, which function as the photon source and directional antenna in the system, respectively. Efficient optical coupling is facilitated by enhanced light scattering at specific sidewall facets of the microring cavity, which can be engineered deterministically during epitaxial growth. Through Fourier imaging, out‐of‐plane laser emission with antenna‐like far‐field directivity in the coupled system is demonstrated. Furthermore, the emission directivity and side mode suppression in the coupled system can be improved significantly by tuning the geometric parameters of the system. The way for low power consumption, on‐chip microlasers with tunable emission directionality is paved here. [ABSTRACT FROM AUTHOR]

Epitaxial complex oxide heterostructures on Si are an excellent platform for the realization of multifunctional electronic devices to exploit the unique functionalities of the oxides that Si does not possess. It is often necessary to make patterns of epitaxial films on selected areas of Si. Here, a path towards the selective area epitaxial growth of complex oxide heterostructures on Si using a hard mask lift-off technique is reported. A water-soluble oxide (Sr3Al2O6) is used as a lift-off hard mask that can survive the high temperature (~ 750 °C) and oxidizing environments for epitaxial oxide growth and be selectively etched away subsequently using deionized water. It is found that the epitaxial growth of yttria-stabilized zirconia (YSZ) buffer layers on Si is very sensitive to organic residues formed during photolithography. Island patterns of epitaxial (La, Sr)MnO3/CeO2/YSZ heterostructures are successfully fabricated on Si through the use of oxygen plasma treatment to remove residues. A simple and low-cost method to pattern complex oxide single crystals integrated on Si for the realization of multifunctional oxide-integrated electronics is provided in this study. [ABSTRACT FROM AUTHOR]

Selective area epitaxy (SAE) provides the path for scalable fabrication of semiconductor nanostructures in a device-compatible configuration. In the current paradigm, SAE is understood as localized epitaxy, and is modelled by combining planar and self-assembled nanowire growth mechanisms. Here we use GaAs SAE as a model system to provide a different perspective. First, we provide evidence of the significant impact of the annealing stage in the calculation of the growth rates. Then, by elucidating the effect of geometrical constraints on the growth of the semiconductor crystal, we demonstrate the role of adatom desorption and resorption beyond the direct-impingement and diffusion-limited regime. Our theoretical model explains the effect of these constraints on the growth, and in particular why the SAE growth rate is highly sensitive to the pattern geometry. Finally, the disagreement of the model at the largest pitch points to non-negligible multiple adatom recycling between patterned features. Overall, our findings point out the importance of considering adatom diffusion, adsorption and desorption dynamics in designing the SAE pattern to create pre-determined nanoscale structures across a wafer. These results are fundamental for the SAE process to become viable in the semiconductor industry. [ABSTRACT FROM AUTHOR]

Gallium nitride (GaN) nanowires by selective area epitaxy (SAE) are an emerging platform for nanophotonic devices. Nonetheless, the use of a high substrate temperature in SAE limits the development of this technology. In this work, we report the SAE of GaN nanowires at low substrate temperatures by radio frequency plasma-assisted molecular beam epitaxy. Excellent selectivity is obtained at low substrate temperatures; the area without patterning is nearly free of any growth. Furthermore, a delicate control on the nanowire top-surface morphology is enabled by the low temperature epitaxy from an irregular shape to a hexagonal shape with semipolar top planes to a hexagonal shape with polar c-planes on top with controlled polar c-plane size. Such a low temperature SAE of GaN nanowires, together with the elegant control of the nanowire top-surface morphology, will enable a fully controllable, epitaxial nanophotonic platform, benefiting the development of a wide range of photonic devices such as light-emitting diodes, lasers, single photon sources, and multifunctional photonic devices. [ABSTRACT FROM AUTHOR]

Gallium phosphide (GaP) is an important optical material due to its visible wavelength band gap and high refractive index. However, the bandgap of the thermodynamically stable zinc blende GaP is indirect, but wurtzite (WZ) structure GaP is direct bandgap. In this work, we demonstrate high-quality and dense GaP vertical nanopillar (NP) array directly on Si (111) substrates through selective area epitaxy (SAE) by MOCVD for the first time, through systemic studies of the effect of TMGa flow rate, growth temperature, and V/III ratio. Uniform GaP NPs are grown over a patterned $400\,\,\mu \text{m}\,\,\times 400\,\,\mu \text{m}$ area with 97.5% yield. Arrays of GaP vertical p-i-n NP diodes are demonstrated with a ideality factor and rectification ratio of 3.7 and 103, respectively. With the high yield of hexagonal structure and electrically proven device quality of GaP NPs through this growth method, this work represents a significant step in achieving GaP NP based optoelectronic devices, such as micro-LEDs emitting in the green wavelength range. [ABSTRACT FROM AUTHOR]

AlzGa1−zAs layers of various compositions were grown using metalorganic chemical vapor deposition on a GaAs substrate with a pattern of alternating SiO2 mask/window stripes, each 100 µm wide. Microphotoluminescence maps and thickness profiles of AlzGa1−zAs layers that demonstrated the distribution of the growth rate and z in the window were experimentally studied. It was shown that the layer growth rate and the AlAs mole fraction increased continuously from the center to the edge of the window. It was experimentally shown that for a fixed growth time of 10 min, as z increased from 0 to 0.3, the layer thickness difference between the center of the window and the edge increased from 700 Å to 1100 Å, and the maximum change in z between the center of the window and the edge reached Δz 0.016, respectively. Within the framework of the vapor -phase diffusion model, simulations of the spatial distribution of the layer thickness and z across the window were carried out. It was shown that the simulation results were in good agreement with the experimental results for the effective diffusion length D/k: Ga—85 µm, Al—50 µm.

Selective area epitaxy (SAE) using metal–organic chemical vapor deposition (MOCVD) is a crucial fabrication technique for lasers and photonic integrated circuits (PICs). A low-cost, reproducible, and simple process for the mass production of semiconductor lasers with specific structures was realized by means of SAE. This paper presents a review of the applications of SAE in semiconductor lasers. Growth rate enhancement and composition variation, which are two unique characteristics of SAE, are attributed to a mask. The design of the mask geometry enables the engineering of a bandgap to achieve lasing wavelength tuning. SAE allows for the reproducible and economical fabrication of buried heterojunction lasers, quantum dot lasers, and heteroepitaxial III–V compound lasers on Si. Moreover, it enables the fabrication of compact photonic integrated devices, including electro-absorption modulated lasers and multi-wavelength array lasers. Results show that SAE is an economical and reproducible method to fabricate lasers with desired structures. The goals for SAE applications in the future are to improve the performance of lasers and PICs, including reducing the defects of the grown material introduced by the SAE mask and achieving precise control of the thickness and composition. [ABSTRACT FROM AUTHOR]

Semiconductor nanowires (NWs) are believed to play a crucial role for future applications in electronics, spintronics and quantum technologies. A potential candidate is HgTe but its sensitivity to nanofabrication processes restrain its development. A way to circumvent this obstacle is the selective area growth technique. Here, in-plane HgTe nanostructures are grown thanks to selective area molecular beam epitaxy on a semi-insulating CdTe substrate covered with a patterned SiO 2 mask. The shape of these nanostructures is defined by the in-plane orientation of the mask aperture along the <110>, <11¯0>, or <100> direction, the deposited thickness, and the growth temperature (GT). Several micron long in-plane NWs can be achieved as well as more complex nanostructures such as networks, diamond structures or rings. A good selectivity is achieved with very little parasitic growth on the mask even for a GT as low as 140 °C and growth rate up to 0.5 monolayer per second. For <110> oriented NWs, the center of the nanostructure exhibits a trapezoidal shape with {111}B facets and two grains on the sides, while <11¯0> oriented NWs show {111}A facets with adatoms accumulation on the sides of the top surface. Transmission electron microscopy observations reveal a continuous epitaxial relation between the CdTe substrate and the HgTe NW. Measurements of the resistance with four-point scanning tunneling microscopy indicates a good electrical homogeneity along the main NW axis and a thermally activated transport. This growth method paves the way toward the fabrication of complex HgTe-based nanostructures for electronic transport measurements., (© 2024 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.)

III-nitride-based micro-light-emitting diodes (micro-LEDs) are currently under rapid development for next-generation high-resolution and high-brightness displays and augmented/virtual reality (AR/VR) technologies. However, it remains elusive to achieve red-emitting III-nitride micro-LEDs with a microscale size, high efficiency, and high spectral stability, posing significant impediments to the development of full-color micro-LEDs. In this work, through detailed strain engineering and control of charge carrier transport, we achieved pure red emission (≥620 nm) micro-LEDs over 2 orders of magnitude of injection current variation. We show both theoretically and experimentally that the combination of a short-period InGaN/GaN superlattice and a thick n-type GaN interlayer can not only relieve the quantum-confined Stark effect in the active region but also suppress parasitic emission from the superlattice. The optimized deep red micro-LEDs with a device lateral dimension of ∼1 μm feature a maximal external quantum efficiency of over 3% emitting at ∼660 nm.

We analyze a method to selectively grow straight, vertical gallium nitride nanowires by plasma-assisted molecular beam epitaxy (MBE) at sites specified by a silicon oxide mask, which is thermally grown on silicon (111) substrates and patterned by electron-beam lithography and reactive-ion etching. The investigated method requires only one single molecular beam epitaxy MBE growth process, i.e., the SiO2 mask is formed on silicon instead of on a previously grown GaN or AlN buffer layer. We present a systematic and analytical study involving various mask patterns, characterization by scanning electron microscopy, transmission electron microscopy, and photoluminescence spectroscopy, as well as numerical simulations, to evaluate how the dimensions (window diameter and spacing) of the mask affect the distribution of the nanowires, their morphology, and alignment, as well as their photonic properties. Capabilities and limitations for this method of selective-area growth of nanowires have been identified. A window diameter less than 50 nm and a window spacing larger than 500 nm can provide single nanowire nucleation in nearly all mask windows. The results are consistent with a Ga diffusion length on the silicon dioxide surface in the order of approximately 1 μm. [ABSTRACT FROM AUTHOR]

Selective area epitaxy (SAE) using metal–organic chemical vapor deposition (MOCVD) is a crucial fabrication technique for lasers and photonic integrated circuits (PICs). A low-cost, reproducible, and simple process for the mass production of semiconductor lasers with specific structures was realized by means of SAE. This paper presents a review of the applications of SAE in semiconductor lasers. Growth rate enhancement and composition variation, which are two unique characteristics of SAE, are attributed to a mask. The design of the mask geometry enables the engineering of a bandgap to achieve lasing wavelength tuning. SAE allows for the reproducible and economical fabrication of buried heterojunction lasers, quantum dot lasers, and heteroepitaxial III–V compound lasers on Si. Moreover, it enables the fabrication of compact photonic integrated devices, including electro-absorption modulated lasers and multi-wavelength array lasers. Results show that SAE is an economical and reproducible method to fabricate lasers with desired structures. The goals for SAE applications in the future are to improve the performance of lasers and PICs, including reducing the defects of the grown material introduced by the SAE mask and achieving precise control of the thickness and composition.

The development of small size, ultracompact photonic devices is required for a wide range of applications, such as next‐generation automobile displays, micro‐light‐emitting diode (µ‐LED) TVs, smart phones and watches, virtual reality, and augmented reality. Here, for the first time, a new approach is reported to dramatically reduce the size of photonic device chips by using a monolithic light reflector‐nanowire LED system. Moreover, the vertical cavity nanowire structure for the surface‐lighting emission is developed by selective area epitaxy that can precisely control the gaps and diameters of the GaN nanowires. The light reflection is provided by high quality Al metal reflector which is directly deposited by molecular beam epitaxy (MBE) technique. The selective area growth shows uniform GaN heterostructure arrays with excellent crystal quality and desired aspect ratio. Furthermore, an advanced selective area etching process is introduced to fabricate Al mirrors between nanowire arrays. Significantly improved light efficiency is observed at ≈550 nm spectral wavelength from the monolithic Al light reflector‐vertical surface emitting nanowire LED system. To break the "green gap" bottleneck in III‐nitride photonics, the approach will open a new route toward monolithic, ultrasmall, electrically pumped nanoscale light emitters for next‐generation photonic and electronic devices. [ABSTRACT FROM AUTHOR]

Increasing quantum confinement in semiconductor quantum dot (QD) systems is essential to perform robust simulations of many-body physics. By combining molecular beam epitaxy and lithographic techniques, we developed an approach consisting of a twofold selective area growth to build QD chains. Starting from 15 nm-thick and 65 nm-wide in-plane In 0.53 Ga 0.47 As nanowires on InP substrates, linear arrays of In 0.53 Ga 0.47 As QDs were grown on top, with tunable lengths and separations. Kelvin probe force microscopy performed at room temperature revealed a change of quantum confinement in chains with decreasing QD sizes, which was further emphasized by the spectral shift of quantum levels resolved in the conduction band with low temperature scanning tunneling spectroscopy. This approach, which allows the controlled formation of 25 nm-thick QDs with a minimum length and separation of 30 nm and 22 nm respectively, is suitable for the construction of scalable fermionic quantum lattices., (© 2024 IOP Publishing Ltd.)

Selective Area van der Waals Epitaxy (SAVWE) of III-Nitride device has been proposed recently by our group as an enabling solution for h-BN-based device transfer. By using a patterned dielectric mask with openings slightly larger than device sizes, pick-and-place of discrete LEDs onto flexible substrates was achieved. A more detailed study is needed to understand the effect of this selective area growth on material quality, device performance and device transfer. Here we present a study performed on two types of LEDs (those grown on h-BN on patterned and unpatterned sapphire) from the epitaxial growth to device performance and thermal dissipation measurements before and after transfer. Millimeter-size LEDs were transferred to aluminum tape and to silicon substrates by van der Waals liquid capillary bonding. It is shown that patterned samples lead to a better material quality as well as improved electrical and optical device performances. In addition, patterned structures allowed for a much better transfer yield to silicon substrates than unpatterned structures. We demonstrate that SAVWE, combined with either transfer processes to soft or rigid substrates, offers an efficient, robust and low-cost heterogenous integration capability of large-size devices to silicon for photonic and electronic applications. [ABSTRACT FROM AUTHOR]

Fabrication of microcavities based on III‐nitrides is challenging due to difficulties with the coherent growth of heterostructures having a large number of periods, at the same time keeping a good precision in terms of thickness and composition of the alloy. A planar design for GaN microresonators supporting whispering gallery modes is suggested. GaN hexagonal microstructures are fabricated by selective‐area metalorganic vapor phase epitaxy using focused ion beam for mask patterning. Low‐temperature cathodoluminescence spectra measured with a high spatial resolution demonstrate two dominant emission lines in the near bandgap region. These lines merge at room temperature into a broad emission band peaking at ≈3.3 eV, which is shifted toward lower energies compared with the reference excitonic spectrum measured for the GaN layer. A numerical analysis of exciton–polariton modes shows that some strongly localized cavity modes can have high Purcell coefficients and can strongly interact with the GaN exciton. [ABSTRACT FROM AUTHOR]

High-quality quantum light sources are crucial components for the implementation of practical and reliable quantum technologies. The persistent challenge, however, is the lack of scalable and deterministic single photon sources that can be synthesized reproducibly. Here, we present a combination of droplet epitaxy with selective area epitaxy to realize the deterministic growth of single quantum dots in nanowire arrays. By optimization of the single quantum dot growth and the nanowire cavity design, single emissions are effectively coupled with the dominant mode of the nanowires to realize Purcell enhancement. The resonance-enhanced quantum emitter system boasts a brightness of millions of counts per second with nanowatt excitation power, a short radiation lifetime of 350 ± 5 ps, and a high single-photon purity with g (2) (0) value of 0.05 with continuous wave above-band excitation. Finite-difference time-domain (FDTD) simulation results show that the emissions of single quantum dots are coupled into the TM 01 mode of the nanowires, giving a Purcell factor ≈ 3. Our technology can be used for creating on-chip scalable single photon sources for future quantum technology applications including quantum networks, quantum computation, and quantum imaging.

Selective area epitaxy (SAE) is widely used in photonic integrated circuits, but there is little information on the use of this technique for the growth of heterostructures in ultra-wide windows. Samples of heterostructures with InGaAs quantum wells (QWs) on GaAs (100) substrates with a pattern of alternating stripes (100-μm-wide SiO2 mask/100-μm-wide window) were grown using metalorganic chemical vapour deposition (MOCVD). It was found that due to a local change in the growth rate of InGaAs QW in the window, the photoluminescence (PL) spectra measured from the edge to the center of the window exhibited maximum blueshifts of 14 and 19 meV at temperatures of 80 K and 300 K, respectively. Using atomic force microscopy, we have demonstrated that the surface morphologies of structures grown using standard epitaxy or SAE under identical MOCVD growth conditions correspond to a step flow growth with a step height of ~1.5 ML or a step bunching growth mode, respectively. In the structures grown with the use of SAE, a strong variation in the surface morphology in an ultra-wide window from its center to the edge was revealed, which is explained by a change in the local misorientation of the layer due to a local change in the growth rate over the width of the window.

In-plane InAs nanowires and nanowire networks show great potential to be used as building blocks for electronic, optoelectronic and topological quantum devices, and all these applications are keen to grow the InAs materials directly on Si substrates since it may enable nanowire electronic and quantum devices with seamless integration with Si platform. However, almost all the in-plane InAs nanowires and nanowire networks have been realized on substrates of III-V semiconductors. Here, we demonstrate the selective area epitaxial growth of in-plane InAs nanowires and nanowire networks on Si substrates. We find that the selectivity of InAs growth on Si substrates is mainly dependent on the growth temperature, while the morphology of InAs nanowires is closely related to the V/III flux ratio. We examine the cross-sectional shapes and facets of the InAs nanowires grown along the 〈110〉, 〈100〉 and 〈112〉 orientations. Thanks to the non-polar characteristics of Si substrates, the InAs nanowires and nanowire networks exhibit superior symmetry compared to that grown on III-V substrates. The InAs nanowires and nanowire networks are zinc-blende (ZB) crystals, but there are many defects in the nanowires, such as stacking faults, twins and grain boundaries. The crystal quality of InAs nanowires and nanowire networks can be improved by increasing the growth temperature within the growth temperature window. Our work demonstrates the feasibility of selective area epitaxial growth of in-plane InAs nanowires and nanowire networks on Si substrates., (© 2023 IOP Publishing Ltd.)

We report on the selective area epitaxy (SAE) of AlGaN/GaN microstructures in stretchable geometric patterns. We have investigated dependence of Al incorporation, lateral/sidewall growth profile and electrical properties of SAE heterostructures on Al/Ga source ratio and mask material. We observe higher Al incorporation along with improvement in heterointerface between the SAE layers with an increase in Al to Ga ratio. AlGaN composition, crystal quality and electrical properties of SAE AlGaN/GaN microstructures are shown to be affected by the choice of mask material. Low resistivity in the range of 0.12-0.35 mΩ cm was measured in these heterostructures. Two terminal current-voltage measurements showed 3-5× higher current density in SAE AlGaN/GaN microstructure devices compared to conventional planar High electron mobility transistor (HEMT). A detailed secondary ion mass spectroscopy (SIMS) profiling on SAE structures showed dependency of unintentional n-type dopants on the mask material. [ABSTRACT FROM AUTHOR]

A site‐ and polarity‐controlled MOVPE growth of 3D‐GaN on Si(111) substrates is established using the polarity‐dependent growth speed of GaN on an intermediate AlN layer. For hydrogenated Si or elevated AlN growth temperatures mixed‐polar growth is observed. N‐polarity could be realized on oxidized Si(111) surfaces by a reduced AlN growth temperature of TAlN = 930 °C. Specific Si crystal facets (e.g., {100}, {11 2 ¯}) are determined as starting points for metal‐polar growth of AlN. By site‐controlled etching in Si, we intentionally expose these additional crystal facets prior to epitaxy to obtain defined starting points for metal‐polar growth. At TAlN = 930 °C, this leads to a site‐controlled growth of metal‐polar GaN, surrounded by N‐polar AlN on Si(111). Thus both, a polarity‐ and site‐controlled epitaxial growth of 3D‐GaN is achieved. The new developed method has been applied to a large variety of structure sizes from 650 nm to 1 mm. The results are supported by a schematic model, explaining the influence of surface termination, in situ desorption, and growth conditions. This paves the way to the development of future 3D‐opto‐electronic devices, directly established on Si. [ABSTRACT FROM AUTHOR]

The authors have investigated the effect of dielectric (SiO2/SiNx) and metal (W) masks on impurity incorporation and electrical properties of selective area epitaxy (SAE) GaN microstructures. It is shown that SAE growths result in highly conductive n-type material. Carrier concentrations greater than metal-nonmetal transition level and low resistivity in the range of 0.18–0.29 mΩ cm were observed from Hall measurements for these structures. Two terminal current-voltage measurements showed a 40× increase in current for SAE GaN microstructure devices compared to that of conventional planar GaN devices. Secondary ion mass spectroscopy (SIMS) measurements of unintentional Si and O dopants in these structures showed dependency on the mask type. Similar dopant and carrier concentrations were obtained from SIMS and Hall data, indicating low compensation from acceptors in the SAE growths. [ABSTRACT FROM AUTHOR]

In this study, we integrated RGB inorganic LEDs onto a sapphire substrate. Blue and green subpixels were monolithically integrated using a selective area growth method, while red subpixels were formed by adhesive bonding and epitaxial lift‐off. The fabricated RGB subpixels could be independently controlled to realize the full color spectrum. [ABSTRACT FROM AUTHOR]

Peapod-like ZnO@C with internal void space has been synthesized by calcination of ZnO/ZnOHF@polydopamine nanorods. By designing both the large void space between particles and external elastic carbon shell, the large volume change of ZnO during charge-discharge process could be effectively relieved. Moreover, the carbon shell functioned as an electronic conductor and elastic barrier, could accelerate the reaction kinetics and confine stable SEI films formation on the outer protective layer to further improve the structural integrity. Benefiting from these structure advantages, the peapod-like ZnO@C presents a prominent electrochemical performance with a retained discharge capacity of 565.1 mA h g −1 at 0.2 A g −1 and high rate capacity of 246.6 mA h g −1 even at 4 A g −1 . [ABSTRACT FROM AUTHOR]

To date, there have been no efficient semiconductor light emitters operating in the green and amber wavelengths. This study reports on the synthesis of InGaN nanowire photonic crystals, including dot-in-nanowires, nanotriangles, and nanorectangles with precisely controlled size, spacing, and morphology, and further demonstrates that bottom-up InGaN photonic crystals can exhibit highly efficient and stable emission. The formation of stable and scalable band edge modes in defect-free InGaN nanowire photonic crystals is directly measured by cathodoluminescence studies. The luminescence emission, in terms of both the peak position (λ ≈ 505 nm) and spectral linewidths (full-width-half-maximum ≈ 12 nm), remains virtually invariant in the temperature range of 5-300 K and under excitation densities of 29 W cm−2 to 17.5 kW cm−2. To the best of our knowledge, this is the first demonstration of the absence of Varshni and quantum-confined Stark effects in wurtzite InGaN light emitters-factors that contribute significantly to the efficiency droop and device instability under high-power operation. Such distinct emission properties of InGaN photonic crystals stem directly from the strong Purcell effect, due to efficient coupling of the spontaneous emission to the highly stable and scalable band-edge modes of InGaN photonic crystals, and are ideally suited for uncooled, high-efficiency light-emitting-diode operation. [ABSTRACT FROM AUTHOR]

A robust shadow mask for fabrication of GaAs-based semiconductor nanostructures via selective area molecular beam epitaxy has been developed. The mask is based on a nano-patterned 100 nm thick Si 3 N 4 -membrane on a Si(100) support wafer. Into the membrane, holes with diameters down to 100 nm have been fabricated. The Si 3 N 4 -membranes have been produced by anisotropic etching of the Si(100) by KOH and the membrane itself is patterned by electron beam lithography and reactive ion etching. The masks are fully compatible with ultra-high vacuum and the growth of (In,Ga,Al)As by molecular beam epitaxy. Test depositions of Ga show that one has to minimize the gap between substrate and mask and diffusion has to be suppressed to obtain a localized deposition governed by the hole diameter. Under optimized conditions we were able to deposite Ga in an area with 100 nm diameter. A GaAs layer, which is deposited on the front side of the mask, allows an in - situ hole size reduction and can be re-evaporated without damaging the mask. [ABSTRACT FROM AUTHOR]

Severe melt-back etching has forced the epitaxy of GaN on Si to use an AlN buffer layer for growing high-quality two-dimensional layers, despite its high resistivity. Herein, we report a metal-based pre-orienting layer (POL) for growing GaN nanostructures (NSs) to replace the traditional AlN buffer layer. Two metals, titanium (Ti) and hafnium (Hf), were evaluated as POLs. We succeeded in fabricating arrays of GaN NSs with highly preferred orientation using selective-area growth. The crystallographic phase of the POLs critically affected the evolved orientation of the crystals. Photoluminescence measurements revealed that GaN NSs with Hf-based POLs were of reasonably high quality. We believe that this result will facilitate broader III-V semiconductor applications using alternative substrates moving beyond conventional Si-based optoelectronics. [ABSTRACT FROM AUTHOR]

In this paper, a normally off Al2O3/AlN/GaN MISFET on Si substrate for achieving high threshold voltage stability and uniformity is obtained based on selective area growth. A thin AlN space layer (SL, ~1 nm) is adopted to GaN-based template, and the AlGaN/GaN het-erostructureis selectivelygrownon the template to naturally form a recessed structure. By insertion of the AlN SL, the Al2O3/AlN/GaN interface trapping and scattering effects are effectively suppressed. As a result, a low threshold voltage hysteresis ( \Delta V\mathrm{ th} , 80 mV at maximum gate sweep voltage of 10 V by dc I – V measurement and smaller than 200 mV in linear region by pulse I – V measurement) and a high peak field-effect mobility ( \mu \sf FE) of 192 cm2/ \textV\cdot \texts are obtained in Al2O3/AlN/GaN MISFET. It is a significant improvement compared with Al2O3/GaN MISFET without AlN SL. The Al2O3/AlN/GaN MISFET also exhibits a maximum drain current ( Id,max) of 620 mA/mm, a low on-resistance ( Rds, \mathrm\scriptscriptstyle ON) of $9.6~\Omega \cdot $ mm, and a high uniformity of {V}_{\mathrm{ th}} (2.5 ± 0.1 V). [ABSTRACT FROM PUBLISHER]

We have investigated the influence of nanohole size on selective-area growth (SAG) of InAs nanowire (NW) arrays on Si(111) substrates by metal-organic chemical vapor deposition. The growth of well-defined and position-controlled InAs NW arrays with united vertical orientation can be achieved on the patterned substrates with a certain range of nanohole size, which paves the way for the fabrication of high-electron-mobility and surrounding-gate transistor arrays using NWs as channels. Moreover, it is found that more than one NW are increasingly likely grown per nanohole as the nanohole size increases, and the NWs become increasingly thin and short. This is considered to be due to the supersaturation of adsorbed species in the nanohole and the intense competition for adatoms among multiple NWs per nanohole. [ABSTRACT FROM AUTHOR]

3D integration of III-V semiconductors with Si CMOS is highly attractive since it allows combining new functions such as photonic and analog devices with digital signal processing circuitry. Thus far, most 3D integration approaches have used epitaxial growth on Si, layer transfer by wafer bonding, or die-to-die packaging. Here we present low-temperature integration of InAs on W using Si 3 N 4 template assisted selective area metal-organic vapor-phase epitaxy (MOVPE). Despite growth nucleation on polycrystalline W, we can obtain a high yield of single-crystalline InAs nanowires, as observed by transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). The nanowires exhibit a mobility of 690 cm 2 /(V s), a low-resistive, Ohmic electrical contact to the W film, and a resistivity which increases with diameter attributed to increased grain boundary scattering. These results demonstrate the feasibility for single-crystalline III-V back-end-of-line integration with a low thermal budget compatible with Si CMOS.

A monolithically integrated four-channel directly modulated laser (DML) array working at the 1.3-μm band is demonstrated. The laser was manufactured by using the techniques of selective area growth (SAG) of the upper separate confinement heterostructure (Upper-SCH) and modified butt-joint method. The fabricated device showed stable single mode operation with the side mode suppression ratio (SMSR) >35 dB, and high wavelength accuracy with the deviations from the linear fitted values <±0.03 nm for all channels. Furthermore, small signal modulation bandwidth >7 GHz was obtained, which may be suitable for 40 GbE applications in the 1.3-μm band. [ABSTRACT FROM AUTHOR]

In recent years, near-equiatomic NiTi alloy has been identified as a sound alternative to replace the conventional Ti6Al4V alloy as the next generation orthopaedic biomaterial because of its lower young modulus and unique shape memory effect. The potential problem of using NiTi alloy is the generation of Ni-rich debris when wear occurs. Surface treatment is therefore needed to improve the wear resistance in order to alleviate the impact of the wear. This paper details the surface treatment of NiTi by laser selective area nitriding for enhancing the wear resistance. This was done by a systematic two-step optimization approach: (1) selecting the appropriate set of laser parameters with an L9 Taguchi experiment to optimize the nitride properties and (2) identifying the optimized surface coverage ratio to maximize the wear resistance. The microstructure and surface profiles of the optimized nitride surface was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), and 3-D profile measurement, respectively. The wear resistance of nitrided surfaces with different coverage ratios were then evaluated using reciprocating wear testing against ultra-high-molecular-weight polyethylene (UHMWPE) in simulated body fluid, i.e., Hanks' solution. [ABSTRACT FROM AUTHOR]

We present a conceptually novel approach to achieve selective area epitaxy of GaN nanowires. The approach is based on the fact that these nanostructures do not form in plasma-assisted molecular beam epitaxy on structurally and chemically uniform cation-polar substrates. By in situ depositing and nitridating Si on a Ga-polar GaN film, we locally reverse the polarity to induce the selective area epitaxy of N-polar GaN nanowires. We show that the nanowire number density can be controlled over several orders of magnitude by varying the amount of predeposited Si. Using this growth approach, we demonstrate the synthesis of single-crystalline and uncoalesced nanowires with diameters as small as 20 nm. The achievement of nanowire number densities low enough to prevent the shadowing of the nanowire sidewalls from the impinging fluxes paves the way for the realization of homogeneous core-shell heterostructures without the need of using ex situ prepatterned substrates. [ABSTRACT FROM AUTHOR]

The selective epitaxial growth of Si1-xGex and the related strain properties were studied. Epitaxial Si1-xGex films were deposited on (100) and (110) orientation wafers and on patterned Si wafers with recessed source and drain structures via ultrahigh vacuum chemical vapor deposition using different growing steps and Ge concentrations. The stepwise process was split into more than 6 growing steps that ranged in thicknesses from a few to 120 nm in order to cover the wide stages of epitaxial growth. The growth rates of SiGe on the plane and patterned wafers were examined and a dependence on the surface orientation was identified. As the germanium concentration increased, defects were generated with thinner Si1-xGex growth. The defect generation was the result of the strain evolution which was examined for channel regions with a Si1-xGex source/drain (S/D) structure. [ABSTRACT FROM AUTHOR]

The selective area growth (SAG) of GaN was implemented on patterned GaN/sapphire templates by hydride vapor phase epitaxy (HVPE) to fabricate regular arrays of Ga-polar GaN microrods. The control of growth parameters such as H 2 /N 2 carrier gas ratio, growth temperature, and absolute NH 3 /HCl gas flow resulted in changes in the growth morphology. In particular, for an optimized mixed-carrier gas ratio of H 2 to N 2 , we achieved vertically well-aligned microrods. The topmost regions of the GaN microrods were terminated with pyramidal facets, indicating typical Ga polarity. The optical properties of the grown microrods were characterized by cathodoluminescence (CL) at a low temperature. This revealed that the GaN microrods had high crystal quality since they exhibited suppressed yellow luminescence as well as strong band edge emission. [ABSTRACT FROM AUTHOR]

Post-growth in situ partial SiNx masking of GaN-based epitaxial layers grown in a molecular beam epitaxy reactor is used to get GaN selective area sublimation (SAS) by high temperature annealing. Using this top-down approach, nanowires (NWs) with nanometer scale diameter are obtained from GaN and InxGa1-xN/GaN quantum well epitaxial structures. After GaN regrowth on InxGa1-xN/GaN NWs resulting from SAS, InxGa1-xN quantum disks (QDisks) with nanometer sizes in the three dimensions are formed. Low temperature microphotoluminescence experiments demonstrate QDisk multilines photon emission around 3 eV with individual line widths of 1-2 meV. [ABSTRACT FROM AUTHOR]