Microstructure of non-polar GaN on LiGaO2 grown by plasma-assisted MBE
We have investigated the structure of non-polar GaN, both on the M - and A-plane, grown on LiGaO2 by plasma-assisted molecular beam epitaxy. The epitaxial relationship and the microstructure of the GaN films are investigated by transmission electron microscopy (TEM). The already reported epi-taxial relationship and for M -plane GaN is confirmed. The main defects are threading dislocations and stacking faults in both samples. For the M -plane sample, the density of threading dislocations is around 1 × 1011 cm-2 and the stacking fault density amounts to approximately 2 × 105 cm-1. In the A-plane sample, a threading dislocation density in the same order was found, while the stacking fault density is much lower than in the M -plane sample.
Characterization of structural defects in semipolar GaN layers grown on patterned sapphire substrates
We present the transmission electron microscopy characterization of GaN layers grown by metal–organic vapor phase epitaxy (MOVPE) and hydride vapor phase epitaxy (HVPE) on patterned sapphire substrates (PSSs). We determined that the predominant I1-type basal stacking faults (BSFs) propagated toward the surface without an annihilation reaction, even when the layer thickness was increased by HVPE, whereas some threading dislocations were annihilated through their coalescence. It is revealed that BSFs were generated owing to the growth on the −c plane facet at the initial stage of MOVPE growth. One way to improve the crystalline quality is to use PSSs with wide terraces to expand the defect-free region.
Structural properties of free-standing 50 mm diameter GaN wafers with (101_0) orientation grown on LiAlO2
(10{und 1}0) GaN wafers grown on (100) face of {gamma}-LiAlO{sub 2} were studied using transmission electron microscopy. Despite good lattice matching in this heteroepitaxial system, high densities of planar structural defects in the form of stacking faults on the basal plane and networks of boundaries located on prism planes inclined to the layer/substrate interface were present in these GaN layers. In addition, significant numbers of threading dislocations were observed. High-resolution electron microscopy indicates that stacking faults present on the basal plane in these layers are of low-energy intrinsic I1type. This is consistent with diffraction contrast experiments.