Optical and structural characterization of GaN thin films at different N to Ga flux ratios

Abstract

GaN films were grown on Si(111) substrates under various beam equivalent pressure (BEP) ratios by plasma-assisted molecular beam epitaxy. The optical properties for the grown samples were studied over a wide spectral range from 200 to 3300 nm using the reflectance spectrum only. It was found that increasing the N/Ga BEP ratio from 17.9 to 46.1 increases the refractive index (n) from 2.05 to 2.38 at wavelength 630 nm (for example), while the optical energy gap (Eg) were found to be in the range between 3.325 to 3.35 eV with no specific trend. The structural properties for the grown films were studied through two types of rocking curve measurements; normal rocking curve (ω-scan) and triple axis rocking curve (ω/2θ-scan). It was found that with decreasing the N/Ga ratio from 46.1 to 17.9 the full width at half maximum decreases from 0.62° to 0.58° for ω-scan and from 0.022° to 0.021° for ω/2θ-scan. Thus, our results showed a clear correlation between the optical-structural parameters and the BEP ratios of N and Ga.