Electrical, optical, and structural properties of GaN films prepared by hydride vapor phase epitaxy

Two sets of undoped GaN films with the thickness of 10-20 pm were prepared by hydride vapor phase epitaxy (HVPE) and characterized by capacitance-voltage (C-V) profiling, microcathodoluminescence (MCL) spectra measurements, MCL imaging, electron beam induced current (EBIC) imaging, EBIC dependence on accelerating voltage, deep levels transient spectroscopy, high resolution X-ray diffraction measurements. The difference in growth conditions was mainly related to the lower (850 degrees C, group 1) or higher (950 degrees C, group 2) growth temperature. Both groups of samples showed similar crystalline quality with the dislocation density close to 10(8) cm(-2), but very different electrical and optical properties. In group 1 samples the residual donors concentration was similar to 10(17) cm(-3) or higher, the MCL spectra were dominated by the band-edge luminescence, and the diffusion length of charge carriers was close to 0.1 mu m. Group 2 samples had a 2-4.5 mu m thick highly resistive layer on top, for which MCL spectra were determined by green, yellow and red defect bands, and the diffusion length was 1.5 times higher than in group 1. We also present brief results of growth at the standard HVPE growth temperature of 1050 degrees C that show the presence of a minimum in the net donor concentration and deep traps density as a function of the growth temperature. Possible reasons for the observed results are discussed in terms of the electrical compensation of residual donors by deep traps. (C) 2014 Elsevier B.V. All rights reserved.