Deep traps spectra in undoped gan films grown by hydride vapor phase epitaxy under various conditions

Decreasing the residual donors density and deep traps spectra densities in undoped GaN films grown by Hydride Vapor Phase Epitaxy (HVPE) is very important for promoting the use of such material in high-voltage/high-power rectifiers, radiation detectors. In this study we studied the effects of changing the growth temperature of undoped HVPE GaN films on these properties. The two groups of undoped GaN HVPE samples analyzed in this study were grown at growth temperature being either 850°C or 950°C. Measurements by means of Capacitance-Voltage (C-V) profiling, deep levels transient spectroscopy, Micro Cathode Luminescence (MCL) spectroscopy and imaging and by Electron Beam Induced Current (EBIC) showed a much lower density of residual donors (by almost two orders of magnitude), of deep electron traps and hole traps (by about an order of magnitude) and considerably (about 1.5 times) longer diffusion length of charge carriers in the films grown at 850°C compared to samples prepared at 950°C. The data obtained indicate that there is an optimal reduced growth temperature (close to 850°C) resulting in lower concentration of shallow donors and deep traps while still preserving the high crystalline quality of the layer. This is of paramount importance for device applications of HVPE grown undoped GaN films.