Effects of rapid thermal annealing on the structural properties of GaN thin films

Effects of rapid thermal annealing (RTA) on the structural properties were investigated in undoped GaN film grown by rf-plasma-assisted molecular beam epitaxy (MBE). Detailed characterizations of the photoluminescence (PL), high-resolution X-ray diffraction and low-frequency noise were conducted on both the as-grown and annealed films. PL and X-ray diffraction measurements showed that the crystallinity of the films improved with RTA at 800 degreesC with significant reduction in the yellow emission. Annealing at 900 degreesC and 1000 degreesC resulted in an increase in the FWHM of the Ti-ray diffraction, indicative of thermal decomposition of the materials. The results are in excellent agreement with our study of low-frequency noise, which demonstrates similar trend in the magnitudes of the Hooge parameters as a function of the annealing temperature, The temperature dependence of the voltage noise power spectra S-nu(f) was examined from 400 K to 80 K in the frequency range between 30 Hz and 100 kHz, At the low-frequency range the fluctuation is dominated by 1/f(gamma) noise, and for f > 1 kHz the noise is dominated by G-R noise processes. Our experimental results show that 800 degreesC is the optimal temperature for RTA, which results in substantial improvements in both the optical, structural and noise properties for the material, whereas annealing at 1000 degreesC is found to result in significant material degradation.