Structural and optical properties of Si-doped GaN

Structural and optical properties of Si-doped GaN thin films grown by metal-organic chemical vapor deposition have been studied by means of high resolution x-ray diffraction (XRD), atomic force microscopy, photoluminescence, photothermal deflection spectroscopy, and optical transmission measurements. The incorporation of silicon in the GaN films leads to pronounced tensile stress. The energy position of the neutral donor bound excitonic emission correlates with the measured stress. The stress induced near band gap luminescence shift is estimated to 19+/-2 meV/GPa. An increasing concentration of dopant impurities in the films leads to asymmetries of the XRD and photoluminescence spectra, which are probably related to a Stress induced inhomogeneous distribution of dopants. Atomic force microscopy observations of surface modulation with increasing silicon doping support this latter statement. Transmission and photothermal deflection spectroscopy measurements are used to determine the band gap energy and Urbach energy of highly doped samples.