GaN and AlN Layers Grown by Nano Epitaxial Lateral Overgrowth Technique on Porous Substrates

Abstract

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.

High Optical Quality Nanoporous GaN Prepared by Photoelectrochemical Etching

“…[7][8][9] Although porous GaN offers a good alternate to grow high quality stress free over layer, yet very little work has been done. Recently, few studies on the bandgap and morphology control in porous GaN through electroless wet chemical and photoelectrochemical etching are reported.…”

“…Apart from improved optical pumping, such template will reduce the dislocation density of the layers to be grown on top of it via nano-ELO process. 8,9 In this letter, we report fabrication and properties of nanoporous GaN prepared by UV-assisted electrochemical etching using HF solution as an electrolyte. A significant photoluminescence (PL) intensity enhancement is observed from porous GaN films.…”

Plasma-assisted molecular beam epitaxy of GaN on porous SiC substrates with varying porosity

“…There has been considerable interest in recent years in using porous (ps) SiC as a substrate to grow epitaxial SiC and GaN with reduced dislocation density [1][2][3][4][5][6]. Porous SiC is prepared by anodizing n-type SiC in hydrofluoric acid (HF) under ultra-violet illumination [7].…”

Growth of Gan on Porous Sic Substrates by Plasma-Assisted Molecular Beam Epitaxy

“…Porous SiC and GaN has recently been explored as promising substrates to grow epitaxial SiC or GaN with reduced dislocation density [1][2][3][4][5][6]. Such porous materials are produced by anodizing n-type SiC in hydrofluoric acid (HF) under ultra-violet illumination [7].…”

“…Preliminary results for GaN growth on porous GaN have shown some promise for improved GaN quality [2][3][4]. It has been speculated that a porous surface may serve as a template for nano-scale lateral epitaxial overgrowth [4], and that a porous substrate layer may be compliant to any lattice and thermal mismatch strains [2][3][4]. In this work we grew GaN films on both porous and non-porous SiC substrate under nominally identical conditions and evaluated the effect of using the porous substrate.…”