In this paper, the defects in hexagonal GaN epitaxial layers grown on (0001) sapphire (Al2O3) substrates by HVPE with a horizontal tube reactor had been studied. The GaN epitaxial layers were etched by means of defect-selective etching (Orthodox etching in molten KOH). The samples were characterized by Scanning Electron Microscopy (SEM) and Cathodoluminescence spectra (CL). From surface morphology and cross-sectional images, the defects could be divided into various types: cracks, low angle grain boundary (LAGB), nano-pipes and dislocations. These different defects were discussed. The cracks were proposed as related to the strain. And the strain could not only come from the lattice mismatch and thermal mismatch between sapphire and GaN layer in their interface, but also from the HVPE growth process. It was found that these screw, mixed and edge type dislocations formed small hexagonal pits after etching. Some pits would be observed in the area near LAGB. Additionally, by CL mapping technique, some non-radiative recombination centers without surface terminations could be probed optically.
[1]
Grzegorz Nowak,et al.
Orthodox etching of HVPE-grown GaN
,
2007
.
[2]
Hai Lu,et al.
Cathodoluminescence mapping and selective etching of defects in bulk GaN
,
2006
.
[3]
Masao Ikeda,et al.
Characterization of threading dislocations in GaN epitaxial layers
,
2000
.
[4]
K. H. Ploog,et al.
X-ray diffraction peak profiles from threading dislocations in GaN epitaxial films
,
2004,
cond-mat/0410510.
[5]
Boleslaw Lucznik,et al.
Defects in GaN single crystals and homoepitaxial structures
,
2005
.