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.
Thermal stability of porous SiC (PSC) with nano-, micro- and double-layer porous
structure is assessed through annealing the material at T=900–1700 0C in vacuum and Ar. Changes in composition of PSC under thermal treatment are correlated with porous structure modification. Limitations in PSC technology and applications due to compositional and structure evolution at high temperatures are discussed.
Influence of high-vacuum annealing at temperatures in the range 1300-1400°C and residual pressure of ~10-6 Torr on the surface of 6H-SiC (0001) wafers has been studied. Auger spectroscopy and RHEED data show that the annealing conditions do not lead to any surface reconstruction of the wafers. Atomic force microscopy reveals atomically flat surface terraces separated by steps of unit-cell height (h = 1.5 nm).
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.
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