Defect density and stress reduction in heteroepitaxial GaN and AlN materials is one of the main issues in group III nitride technology. Recently, significant progress in defect density reduction in GaN layers has been achieved using lateral overgrowth technique. In this paper, we describe a novel technique based on nano-scale epitaxial lateral overgrowth. GaN layers were overgrown by hydride vapour phase epitaxy (HVPE) on porous GaN. Porous GaN was formed by anodization of GaN layers grown previously on SiC ŝubstrates. Pore’s size was in nano-scale range. Thickness of overgrown layers ranged from 2 to 120 microns. It was shown that GaN layers overgrown on porous GaN have good surface morphology and high crystalline quality. The surface of overgrown GaN material was uniform and flat without any traces of porous structure. Raman spectroscopy measurements indicated that the stress in the layers grown on porous GaN was reduced down to 0.1 - 0.2 GPa, while the stress in the layers grown directly on 6H-SiC substrates remains at its usual level of about 1.3 GPa. Preliminary experiments were done on HVPE growth of AlN layer on porous substrates. Improvement of surface morphology and crack density reduction has been observed.

The lack of GaN substrates is a limiting factor for the development of III-V nitride devices.Recently we proposed to use GaN/SiC epitaxial wafers, consisting of thin GaN layer depositedby hydride vapor phase epitaxy (HVPE) on SiC wafer, as substrates for subsequent growth of IIIVnitrides and devices development. These wafers are attractive to be used as substrates for GaNdevice fabrication because the GaN-based device structures can be grown on these wafers byhomoepitaxy without any buffer layer. Due to high SiC thermoconductivity and cleavagepossibility, these wafers are especially attractive for high-power electronic and optoelectronicapplications. In this paper, we focus on crystal structure, optical and electrical properties of GaNhomoepitaxial layers and p-n structures grown by HVPE on GaN/SiC epitaxial wafers. Newtypes of III-V nitride epitaxial wafers are described, insulating GaN/SiC epitaxial wafers andAIN/SiC epitaxial wafers.

GaN films of different thicknesses grown on 6H-SiC (00.1) by hydride vapor-phase epitaxy(HVPE) method were characterized by high resolution X-ray diffractometry and synchrotron X-ray topography. Calculations of thermal stresses gave approximately same results as experimental stress indicating that most of the stress in the film is due to the difference in thermal expansion coefficient between the film and substrate. The lowest dislocation density (i.e. 6.64×108 cm−2) in GaN was estimated for the sample, which has the highest thickness of GaN layer. Also comparing two different 6H-SiC substrates grown by sublimation and Lely techniques, the substrate grown by sublimation was found to be the better substrate to grow GaN thin film with lower dislocation density. Synchrotron X-ray topography revealed a number of defects including mosaic structure or local bending, low angle grain boundaries, cracks and micropores. Micropores originated at the 6H-SiC substrate went all the way through GaN films as revealed in the reflection topographs.

In this paper, we describe a novel technique, which shows a high potential for defect densities and stress reduction in SiC and GaN, both epitaxial and bulk. This technique is based on nanometer scale epitaxial lateral overgrowth (NELOG) method, which employs porous substrate materials. This technique does not require any mask and may be easily scaled for large area substrates.SiC layers were grown on porous SIC by sublimation sandwich method. Porous SiC substrates were formed by surface anodization of SiC commercial wafers.GaN layers were overgrown by hydride vapour phase epitaxy on porous GaN. Porous GaN was formed by anodization of single crystal GaN layers grown previously on SiC substrates.Epitaxial layers grown on porous buffer layers were investigated in terms of crystal structure, residual stress, and optical properties.

We have studied epitaxial GaN layers grown by hydride vapour phase epitaxy (HVPE) on porous GaN sublayers formed on SiC substrates. It was shown that these layers can be grown with good surface morphology and high crystalline quality. X-ray, Raman and photoluminescent (PL) measurements showed that the stress in the layers grown on porous GaN was reduced to 0.1-0.2 GPa, while the stress in the layers grown directly on 6H-SiC substrates remains at its usual level of about 1 GPa. Thus, we have shown that growth on porous GaN sublayer is a promising method for fabrication of high quality epitaxial layers of GaN with low strain values.