Properties of GaN films grown under Ga and N rich conditions with plasma enhanced molecular beam epitaxy

GaN growth mediated by electron cyclotron resonance activated nitrogen has been investigated under Ga and nitrogen rich conditions in a substrate temperature range of 650-850 °C. A biasable grid installed between the substrate and nitrogen flux allowed control of the nitrogen species participating in the growth process. The absence of high energetic ions resulted to films with increased photoluminescence signals in the 480-650 nm spectral range. In the Ga rich conditions, the Ga and N ion flux values used were 5×10¹⁴ and 3.5×10¹⁴ cm^-2 s ^-1, respectively. The nitrogen rich conditions were achieved by increasing the N flux first to 8×10¹⁴ and then to 1.2×10¹⁵ cm^-2 s^-1. Both types of samples exhibited strong band edge photoluminescence signal at room temperature, with N rich conditions leading to better mobilities and lower carrier concentrations. The best films were obtained when the substrate temperature was 750 °C.