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High-performance long-wavelength InAs/GaSb superlattice detectors grown by MOCVD
摘要： We demonstrate high-performance long-wavelength InAs/GaSb superlattice (SL) infrared photodetectors based on an Al-free single heterojunction grown by metalorganic chemical vapor deposition (MOCVD). The device structure consists of a mid-wavelength InAs/GaSb SL p-n junction (PN) and a long-wavelength InAs/GaSb SL n-type absorber (n), so-called PNn design, to reduce the dark current. In addition, a shallow etch technique was employed by exposing only mid-wavelength materials during pixel isolation to suppress surface leakage currents. At 77 K and a bias voltage of -0.1 V, the device exhibited a 50% cut-off wavelength at 8.0 μm, a dark current density of 2.4×10-5 A/cm2, and a peak responsivity of 2.1 A/W. Temperature dependent dark current measurement indicated diffusion-limited behavior down to 75 K. The specific detectivity was estimated to be 7.3×1011 cm·Hz1/2/W, which is comparable with that of detectors grown by molecular beam epitaxy (MBE) at similar cut-off wavelengths.
关键词： InAs/GaSb type-II superlattices,metalorganic chemical vapor deposition,heterostructure,long-wavelength infrared
更新于2025-09-23 15:22:29
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Revealing the Role of Gold in the Growth of Two-dimensional Molybdenum Disulfide by Surface Alloy Formation
摘要： Formation of Mo-Au surface alloy during Au-assisted chemical vapor deposition (CVD) of MoS2 was confirmed by a series of control experiments. We adapted a metalorganic chemical vapor deposition (MOCVD) system to conduct two-dimensional MoS2 growth in a controlled environment. Sequential injection of Mo and S precursors, which does not yield any MoS2 on a SiO2/Si, grows atomically thin MoS2 on Au, indicating formation of an alloy phase. Transmission electron microscopy of a cross-section of the specimen confirmed the confinement of the alloy phase near the surface only. These results show that the reaction intermediate is the surface alloy and that the role of Au in the Au-assisted CVD is formation of an atomically thin reservoir of Mo near the surface. This mechanism is clearly distinguished from that of MOCVD, which does not involve formation of any alloy phases.
关键词： Molybdenum Disulfide,Surface Alloy,Two-dimensional Material,Chemical vapor deposition,Metalorganic Chemical Vapor Deposition
更新于2025-09-23 15:21:01
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Controlled growth of InGaN quantum dots on photoelectrochemically etched InGaN quantum dot templates
摘要： Controlled growth of InGaN quantum dots (QDs) using photoelectrochemically (PEC) etched InGaN QD templates is demonstrated. The InGaN QDs are grown by a self-assembly (SA) method using metal-organic chemical vapor deposition on templates consisting of planar GaN and PEC etched InGaN QDs for comparison. The InGaN QD templates are formed using quantum-size-controlled PEC etching of planar InGaN layers on GaN, which produces controlled QD radiuses with a statistical mean (μ) of 17.3 nm and standard deviation (σ) of 6.2 nm, and densities of 1.2 × 1010 cm?2. The PEC etched QDs are capped with an AlGaN interlayer and GaN barrier layer to recover a planar surface morphology for subsequent SA growth of QDs. The PEC QD templates behave as seeds via localize strain near the PEC QDs which provide improved control of the SA QD growth. The SA grown QDs on PEC QD templates are smaller and have controlled radiuses with μ = 21.7 nm and σ = 11.7 nm compared to the SA QDs on planar GaN templates with radiuses of μ = 37.8 nm and σ = 17.8 nm. Additionally, the dot densities of the SA QDs on PEC QD templates are ~3 times higher and more closely match the underlying densities of the template (8.1 × 109 cm?2). Multiple quantum dots (MQDs) are also grown on both templates that consist of 4 periods of SA QDs and AlGaN/GaN interlayer/barrier layers. The MQDs grown on PEC QD templates better retain their planarized smooth surfaces after barrier layer growth, and exhibit ~3 times stronger PL intensity at room temperature compared to MQDs grown on planar GaN.
关键词： Metalorganic chemical vapor deposition,Nitrides,Quantum dots,Light emitting diodes,Atomic force microscopy,Photoelectrochemical etching
更新于2025-09-23 15:21:01
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Low-temperature growth of n<sup>++</sup>-GaN by metalorganic chemical vapor deposition to achieve low-resistivity tunnel junctions on blue light emitting diodes
摘要： We report on low-resistivity GaN tunnel junctions (TJ) on blue light-emitting diodes (LEDs). Si-doped n++-GaN layers are grown by metalorganic chemical vapor deposition directly on LED epiwafers. Low growth temperature (< 800 °C) was used to hinder Mg-passivation by hydrogen in the p++-GaN top surface. This allows achieving low-resistivity TJs without the need for post-growth Mg activation. TJs are further improved by inserting a 5 nm thick In0.15Ga0.85N interlayer (IL) within the GaN TJ thanks to piezoelectric polarization induced band bending. Eventually, the impact of InGaN IL on the internal quantum efficiency of blue LEDs is discussed.
关键词： metalorganic chemical vapor deposition,GaN tunnel junctions,blue light-emitting diodes
更新于2025-09-23 15:21:01
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Epitaxial lateral overgrowth of GaN on nano-cavity patterned sapphire substrates
摘要： The epitaxial lateral overgrowth of GaN by metal-organic chemical vapor deposition using a nano-cavity patterned sapphire substrate (NCPSS) was investigated. The NCPSS, with a hexagonal non-close-packed nano-cavity pattern on the sapphire substrate, was fabricated by polystyrene sphere coating and size reduction by reactive ion etching, followed by deposition of alumina and thermal oxidation. The coalescence of GaN on the NCPSS was achieved by the formation of relatively large GaN islands and enhanced lateral overgrowth of the GaN islands over several nano-cavity pattern areas. The threading dislocation density (TDD) measured by cathodoluminescence measurement was significantly reduced from 2.4 108 cm-2 to 6.9 107 cm-2 by using the NCPSS. Dislocation behaviors that contribute to the reduction of TDD of the GaN layer were observed by transmission electron microscopy. Raman spectroscopy revealed that the compressive stress in the GaN layer was reduced by 21% due to the embedded nano-cavities. In addition, the diffuse reflectance of GaN on the NCPSS was enhanced by 54% ~ 62%, which is attributed to the increased probability of light extraction through effective light scattering by nano-cavities.
关键词： A1. Nanostructures,B1. Nitrides,A2. Single crystal growth,A3. Metalorganic chemical vapor deposition,A3. Nanoscale epitaxial lateral overgrowth
更新于2025-09-23 15:21:01
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Characterization of Epitaxial ?2-(Al,Ga,In)2O3-Based Films and Applications as UV Photodetectors
摘要： Epitaxial ?lms of b-(AlxGa1?x)2O3, b-Ga2O3, and b-(InxGa1?x)2O3 were grown on (001) sapphire substrates via metalorganic chemical vapor deposition (MOCVD). The compositions of the ?lms as determined from energy dispersive x-ray analysis (EDX) and x-ray photoelectron spectroscopy (XPS) results were XAl = 0.57 ± 0.05 and 0.76 ± 0.05 and XIn = 0.12 ± 0.05 and 0.21 ± 0.05. The optical bandgap was found to correspondingly vary between 6.0 ± 0.2 and 3.9 ± 0.1 eV, as a function of composition via XPS and UV–visible spectroscopy (UV–Vis). X-ray diffraction, scanning electron microscopy, and atomic force microscopy revealed the ?lms to be highly-oriented with nanocrystalline domains. Schottky- and MSM-based solar-blind UV photodetectors were fabricated on the ?lms and showed responsivities at 20 V varying from > 104 A/W for the Ga2O3 devices, > 103 A/W for the (AlxGa1?x)2O3 devices and > 102 A/W for the (InxGa1?x)2O3 devices. Modest shifts in wavelength selectivity corresponding with the changes in composition/bandgap were also measured. Time response measurements on Schottky and MSM detectors reveal rise and dwell times on the order of a minute, indicating the presence of photoconductive gain. Noise-equivalent powers were in the fW–pW regime with speci?c detectivities (D?) between 1010 and 1012 Jones. Scanning photocurrent maps display large photocurrent generation at the Schottky interface in the case of a b-Ga2O3 Schottky detector, whereas for an b-(InxGa1?x)2O3 MSM detector the photocurrent generation occurs in the device channel and at the Schottky interface.
关键词： b-(AlxGa1?x)2O3,b-(InxGa1?x)2O3,b-Ga2O3,Metalorganic chemical vapor deposition
更新于2025-09-23 15:19:57
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Influence of trimethylaluminum predoses on the growth morphology, film-substrate interface, and microstructure of MOCVD-grown AlN on (111)Si
摘要： Aluminum nitride (AlN) was deposited on (111) silicon by metalorganic chemical vapor deposition after varied trimethylaluminum predoses. Growth morphologies, film-substrate interfaces, and film microstructures were examined using scanning electron microscopy, atomic force microscopy, X-ray diffraction, and transmission electron microscopy. In samples grown with predoses, lateral growth was observed over faceted "patches" formed during the predose. Three-dimensional growth was observed to seed from small islands on the surface of these patches and eventually overgrow them. The three-dimensional growth mode was similar to that observed when AlN was grown without a predose, resulting in similar morphologies in all films, regardless of predose, after the islands coalesced. The AlN-silicon interface was found to be predominantly amorphous when no predose was used. However, narrow regions were observed over which the film was in atomic registry with the substrate. This indicates AlN nucleates in epitaxy with the substrate and amorphous silicon nitride forms between nucleation sites due to ammonia exposure. Films grown with predoses had structurally abrupt interfaces, suggesting aluminum within the observed patch features inhibits the reaction between ammonia and silicon at the onset of growth. A structure distinct from both wurtzite AlN and diamond cubic silicon was observed at the substrate interface in films grown with a predose, consistent with either zinc blende AlN or a strained Si/Al alloy. A mosaic microstructure was observed in all films, grown with or without predoses, which consisted of sub-boundaries formed by clusters of threading dislocations. Threading dislocations, separated by hundreds of nanometers, were found to be tilted along common directions, providing evidence for a dislocation bending mechanism possibly enhanced by the predose.
关键词： Defects,Crystal morphology,Metalorganic chemical vapor deposition,Semiconducting aluminum compounds,Nucleation,Nitrides
更新于2025-09-19 17:15:36
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GaN grown by metalorganic vapor phase epitaxy
摘要： We report on residual impurities in semi-polar (3031) and (2021) GaN homo-epitaxial layer grown by metal-organic chemical vapor deposition. The (3031) and (2021) GaN layer showed atomically smooth surface and clear steps toward [0001] and [000-1], respectively. The residual impurity concentrations of oxygen and carbon were below the detection limit of secondary-ion mass spectroscopy. Low-temperature photoluminescence revealed that (2021) GaN layer consisted free excitons and Si donor bound excitons, along with two-electron satellite lines and longitudinal optical (LO) phonon coupling transitions. The results indicate semi-polar (3031) and (2021) GaN epitaxial layers are promising candidates in obtaining a high quality GaN drift layer for vertical GaN devices.
关键词： B2. Semiconducting III-V materials,A3. Metalorganic chemical vapor deposition,B1. Nitrides,A1. Crystal structure,A1. Impurities
更新于2025-09-19 17:15:36
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Effect of bending test on the performance of CdTe solar cells on flexible ultra-thin glass produced by MOCVD
摘要： The development of lightweight and flexible solar modules is highly desirable for high specific power applications, building integrated photovoltaics, unmanned aerial vehicles and space. Flexible metallic and polyimide foils are frequently used, but in this work an alternative substrate with attractive properties, ultra-thin glass (UTG) has been employed. CdTe solar cells with average efficiency reaching 14.7% AM1.5G efficiency have been produced on UTG of 100 μm thickness. Little has been reported on the effects on PV performance when flexed, so we investigated the effects on J-V parameters when the measurements were performed in 40 mm and 32 mm bend radius, and in a planar state before and after the bend curvature was applied. The flat J-V measurements after 32 mm bending test showed some improvement in efficiency, Voc and FF, with values higher than the first measurement in a planar state. In addition, two CdTe solar cells with identical initial performance were subjected to 32 mm static bending test for 168 hours, the results showed excellent uniformity and stability and no significant variation on J-V parameters was observed. External quantum efficiency and capacitance voltage measurements were performed and showed no significant change in spectral response or carrier concentration. Residual stress analysis showed that no additional strain was induced within the film after the bending test and that the overall strain was low. This has demonstrated the feasibility of using CdTe solar cells on UTG in new applications, when a curved module is required without compromising performance.
关键词： Ultra-thin glass,Thin films,Metalorganic chemical vapor deposition,CdTe solar cells,Bending test
更新于2025-09-19 17:13:59
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MOCVD Growth and Characterization of InN Quantum Dots
摘要： Metal-polar InN quantum dots (QDs) are grown by metalorganic chemical vapor deposition at temperatures between 500 and 600 °C. Dot densities between 4 × 10^8 and 4 × 10^10 cm^-2 are observed. InN QDs exhibit room-temperature photoluminescence (PL) with peak wavelengths from 1100 to >1550 nm. GaN cap layers grown on InN QDs have little effect on either peak PL wavelength or intensity, a step toward creating multilayer structures for InN QD devices.
关键词： quantum dots,thin films,metalorganic chemical vapor deposition,nitrides
更新于2025-09-19 17:13:59