We hive developed a unique approach combining migration-enhanced metalorganic chemical vapor deposition (MEMOCVD) high temperature AIN buffer layers and AlGaN/AIN superlattices (SLs) to yield high quality ( HQ) AlGaN layers for 250 nm LEDs. Symmetric/asymmetric X-ray diffraction (XRD) and room temperature photoluminescence measurements were used to study the high-structural and optical quality. The (002) and (114) rocking curve full width at half -maximum (FWHM) of 1.4 mu m n-Al0.75Ga0.25N grown over AlGaN/AlN buffer were 143 and 565 arcsec, respectively. Crack-free Al0.75Ga0.25N layers with electron concentration as high as 1x10(18) cm and Hall mobility about 50 cm(2)/V.s were successfully grown and used for sub-milliwatt power (0.12 mW at a pulse pump current of 300 mA) 250 nm deep iiltraviolet light emitting diodes (UVLEDs). In addition, for comparison, we prepared n-AlGaN only using high temperature AIN without SLs inserted. The experiments show that the AlGaN/AIN SLs inserted play. crucial role in improving structural and optical quality of high Al-composition AlGaN epilayers. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

a-plane GaN templates and coalesced epitaxial lateral overgrown (ELOG) films on r-plane sapphire substrates were investigated by x-ray diffraction (XRD). The a-plane GaN templates were found to have [0001]-oriented stripe-features, which is related to anisotropic mosaicity. For the mosaic blocks, the mosaicity reached the largest and the smallest values along the [11̄00] and the [0001] directions. The ELOG procedure with the SiO2 mask stripes perpendicular to the [0001] direction limits the preferable growth along this direction, and thereby enhances the [11̄00] growth. This leads to large-area, featureless, a-plane GaN films for which the wing tilt and not the fine mosaic block size becomes the major XRD line-broadening mechanism.

a-plane GaN templates and coalesced epitaxial lateral overgrown (ELOG) films on r-plane sapphire substrates were investigated by x-ray diffraction (XRD). The a-plane GaN templates were found to have [0001]-oriented stripe-features, which is related to anisotropic mosaicity. For the mosaic blocks, the mosaicity reached the largest and the smallest values along the [11̄00] and the [0001] directions. The ELOG procedure with the SiO2 mask stripes perpendicular to the [0001] direction limits the preferable growth along this direction, and thereby enhances the [11̄00] growth. This leads to large-area, featureless, a-plane GaN films for which the wing tilt and not the fine mosaic block size becomes the major XRD line-broadening mechanism.

a-plane GaN templates and coalesced epitaxial lateral overgrown (ELOG) films on r-plane sapphire substrates were investigated by x-ray diffraction (XRD). The a-plane GaN templates were found to have [0001]-oriented stripe-features, which is related to anisotropic mosaicity. For the mosaic blocks, the mosaicity reached the largest and the smallest values along the [1 (1) over bar 00] and the [0001] directions. The ELOG procedure with the SiO2 mask stripes perpendicular to the [0001] direction limits the preferable growth along this direction, and thereby enhances the [1 (1) over bar 00] growth. This leads to large-area, featureless, a-plane GaN films for which the wing tilt and not the fine mosaic block size becomes the major XRD line-broadening mechanism. (C) 2004 American Institute of Physics.

We investigated the growth of GaN/Al0.20Ga0.80N multiple quantum wells (MQWs) on selective-area-grown a-plane GaN pillars over r-plane sapphire. In contrast to the MQWs grown on planar a-plane GaN templates, these GaN/Al0.20Ga0.8N MQWs on the pillars exhibited pit-free and atomically smooth surface morphology. Their structural quality and their UV emission (at 357 nm) increased with the underlying pillar height. The epitaxy of GaN/AlGaN MQWs on the selective-area-grown pillars is thus a promising and simple approach for fabricating stripe-geometry, high-efficiency, nonpolar UV emitters.

We report a new epitaxy procedure for growing extremely low defect density a-plane GaN films over r-plane sapphire. By combining selective area growth through a SiO2 mask opening to produce high height to width aspect ratio a-plane GaN pillars and lateral epitaxy from their c-plane facets, we obtained fully coalesced a-plane GaN films. The excellent structural, optical and electrical characteristics of these selective area lateral epitaxy (SALE) deposited films make them ideal for high efficiency III-N electronic and optoelectronic devices.

Fully coalesced epitaxial laterally overgrown a-plane GaN films were characterized for their structural and optical quality. The films had a very smooth surface with a root mean square roughness as low as 4.6 Å for a 5 µm × 5 µm atomic force microscope scan area. They exhibited a wing tilt of only 0.27° and optically pumped stimulated emission, which establish their high structural and optical quality. These non-polar films are ideal for fabricating high-efficiency optoelectronic and electronic devices.