Defect reduction mechanisms in the nanoheteroepitaxy of GaN on SiC

Abstract

This article describes defect reduction mechanisms that are active during the growth of GaN by nanoheteroepitaxy on (0001) 6H SiC. Nanoheteroepitaxial (NHE) and planar GaN epitaxial films were grown and compared using transmission electron microscopy, photoluminescence, x-ray diffraction, and time resolved photoluminescence. It was found that in addition to the previously reported defect reduction mechanism that results from the high compliance of nanoscale nuclei, other independent defect reduction mechanisms are also active during NHE including: (i) filtering of substrate defects, (ii) improved coalescence at the nanoscale, and (iii) defect termination at local free surfaces. Also, it was found that the biaxial strain in the GaN film could be significantly reduced by using a “grouped” NHE pattern geometry. Time resolved photoluminescence measurements on NHE GaN samples with this geometry showed a more than tenfold increase in carrier lifetime compared to GaN grown on planar SiC.

GaN nano‐pendeo‐epitaxy on Si(111) substrates

“…Not all dislocations existing in the seed propagate through to the surface of the overgrown layer, instead some are bent and annihilated in the NPE-GaN process [25,26,31]. These generally result in the reduction of dislocations.…”

“…Growth on patterned substrates on the nanoscale has made good progress in recent years both theoretically [19,20] and experimentally, including GaN growth on silicon substrates [21][22][23][24][25] and on silicon carbide [26] by metalorganic vapour phase epitaxy (MOVPE) [21][22][24][25][26] and molecular beam epitaxy (MBE) [23]. Dislocations are reduced and cracks are suppressed by using this nanoheteroepitaxy technique.…”

“…Two possible strain reduction mechanisms contribute to the reduced cracking. Firstly, the strain in the NPE-GaN layer from the nano-heteroepitaxy is relaxed through a three dimensional deformation of the nanocolumns before coalescence [19][20][21][22][23][24][25][26]. Secondly, probably a more important route for tensile strain built up during the coalescence and cool-down phases to release is through nanocolumn deformation, with some even breaking to accommodate the strain energy after cool-down.…”

Photonic crystal structure effect on the enhancement in the external quantum efficiency of a red LED

“…Despite these promises, the development of high efficiency HB LEDs has been limited because of poor external quantum efficiency, low internal quantum efficiency caused by defects in the epitaxy, and device parasitics [2]- [4]. Among these issues, the external quantum efficiency has been considered to be the most crucial.…”

Luminescence Decay Kinetics in GaN Studied by Frequency Domain Measurements

“…Extensive studies on nitrides indicate that the quality of III-nitride epilayers is still a major challenge, as the layers still contain large densities of defects. The quality of GaN epilayers is often characterized by the nonequilibrium carrier lifetime [1,2], which is usually extracted from the time-resolved photoluminescence experiments. However, the reported time-resolved measurements were performed at relatively high excitation levels, when nonradiative and defect-related radiative recombination channels might have been partially or completely saturated and their effect on the carrier lifetime was reduced or eliminated.…”