Growth and properties of Al-rich InxAl1−xN ternary alloy grown on GaN template by metalorganic chemical vapour deposition

An Al-rich InxAl1−xN ternary alloy was grown on a GaN template by metal–organic chemical vapour deposition (MOCVD). The GaN template was fabricated on a c-plane sapphire with a low temperature GaN nucleation layer. The growth of the 300 nm thick InxAl1−xN layer was carried out under various growth temperatures and pressures. The surface morphology and the InN molar fraction of the InxAl1−xN layer were assessed by using atomic force microscopy (AFM) and high resolution x-ray diffraction, respectively. The AFM surface images of the InxAl1−xN ternary alloy exhibited quantum dot-like grains caused by the 3D island growth mode. The grains, however, disappeared rapidly by increasing diffusion length and mobility of the Al adatoms with increasing growth temperature and the full width at half maximum value of ternary peaks in HR-XRD decreased with decreasing growth pressure. The MOCVD growth condition with the increased growth temperature and decreased growth pressure would be effective to grow the InxAl1−xN ternary alloy with a smooth surface and improved quality. The optical band edge of InxAl1−xN ternary alloys was estimated by optical absorbance and, based on the results of HR-XRD and optical absorbance measurements, we obtained the bowing parameter of the InxAl1−xN ternary alloy at b = 5.3 eV, which was slightly larger than that of previous reports.

Source:IOPscience

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Optical and structural characterization of GaInN/GaN multiple quantum wells grown on nonpolar a-plane GaN templates by metalorganic vapor phase epitaxy

Typical multi quantum well (MQW) grown on nonpolar a-plane GaN templates shows many pits composed of several semipolar planes, and these pits emit at different wavelengths due to the variation of indium incorporations into the QW. In this study, a surface-recovery GaN layer and high-temperature grown barrier were introduced to improve the a-plane MQW quality. We succeeded in decreasing the pits prior to the MQW growth and improving the interfaces of MQW. The structural and optical properties of the MQW were significantly improved.

Source:IOPscience

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Thick GaN Grown on a Nanoporous GaN Template by Hydride Vapor Phase Epitaxy

High-quality thick gallium nitride (GaN) films were overgrown by hydride vapor phase epitaxy (HVPE) on a nanoporous GaN template which was prepared by inductively coupled plasma etching employing an anodized aluminum oxide mask. An obvious reduction of the dislocation density in the thick GaN layer was demonstrated by high-resolution X-ray diffraction, which exhibited the improved crystalline quality in GaN films overgrown on a nanopatterned surface. Moreover, the peak redshift in photoluminescence and micro-Raman spectroscopy indicates a significant strain relaxation in the HVPE-GaN layer. Compared with conventional overgrowth, such a deposition pathway is a more promising technique for the growth of thick GaN layers.

Source:IOPscience

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The impact of purging on the quality of AlGaN/GaN multiple quantum wells grown on AlN/sapphire template

The ultraviolet (UV) emitting AlGaN/GaN multiple quantum wells (MQWs) were grown on low dislocation density AlN/sapphire templates by metal-organic chemical vapor deposition (MOCVD). The impact of the purg time on the interface quality of the AlGaN/GaN quantum well was studied. The high resolution x-ray diffraction (XRD) measurement results demonstrate that the density of dislocations was reduced significantly with the purge time after growth of AlGaN barrier layer and GaN well layer was determined to be 4 min and 2 min, respectively. The mechanism of defect formation in quantum wells was investigated by scanning electron microscope (SEM) measurement.

Source:IOPscience

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Selective Defect Blocking by Self-Assembled Silica Nanospheres for High Quality GaN Template

We demonstrate the use of self-assembled silica nanospheres as a mask to block the propagation of threading dislocations on a defect selective etched GaN template. The selective etched pits were generated on the latent dislocations of GaN template using the wet etching technique. The silica nanospheres (500 nm) were then coated on the selective etched GaN using a spin-coating method. The silica nanospheres were confined in the etched pits by capillary force and geometric shape. The GaN template was then regrown by epitaxial overgrowth using metallorganic chemical vapor deposition. As a result, the regrown GaN layer was significantly reduced from  to  in threading dislocation density and from  to  in etched pit density. These significant enhancements are attributable to selective defect blocking by self-assembled silica nanospheres.

Source:IOPscience

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Improved Performance of Near-Ultraviolet Light Emitting Diodes on Selectively Etched GaN Templates

An approach that dramatically improved the performance of near-ultraviolet InGaN-based light-emitting diodes (NUV-LEDs) was proposed using the selectively etched GaN (SE-GaN) template, which was fabricated via a combination of patterned sapphire substrate (PSS), defect selective etching, SiO2 deposition and chemical-mechanical planarization. The dislocation density of n-type GaN regrown on the SE-GaN template can be reduced to 1.3 × 105 cm−2 by concentrating threading dislocations (TDs) within undoped GaN and terminating the propagation of concentrated TDs. When operated with an injection current of 350 mA, the output power of the NUV-LED fabricated on SE-GaN template was 13% higher than that of NUV-LED fabricated on PSS.

Source:IOPscience

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Growth of High-Quality GaN Template from Nanometer-Size Lattice Channels by Hydride Vapor Phase Epitaxy

GaN are an attractive material in power devices for energy-saving measures in consumer products, automobiles, and industrial machines. To realize such GaN devices, however, high-quality GaN substrates are indispensable. In this paper, we describe the growth of high-crystalline-quality GaN template by HVPE with the nano-FIELO technique, where GaN growth starts by forming facet structures from nanometer-size channels which are opened on SiO2 layer deposited on GaN/sapphire substrate. The lattice pattern consisting of 500 nm × 500 nm square SiO2 masks surrounded by 80-nm-wide channels is used in this study. A nanoimprinting technique is applied followed by dry etching to fabricate lattice channels. From cross-sectional TEM observation, it is shown that the dislocation density is significantly reduced by the lattice pattern. Uniform GaN growth over 2-inch-diameter wafer is realized.

Source:IOPscience

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