GaN deposition characteristics in a UHV-compatible plasma-sputter source
A UHV-compatible plasma-sputter source was used to deposit GaN thin films on SiO2 substrates. The base pressure (in the order of 10-6 Pa) was lower than a rubber gasket-based plasma source and reduced the oxygen contamination prior to film deposition. In this UHV setup equipped with W filaments for discharge cathodes, the deposition target was positioned at a location hidden from direct W evaporation from the filaments. Two growth parameters, the nitrogen and Ga fluxes were controlled by adjusting the discharge current of the plasma and the bias voltage applied to the Ga sputtering target. The estimated nitrogen flux was in the order of 1016/cm2 at a discharge current of 2 A. The Ga flux was changed by adjusting the target bias voltage from 200 to 500 V. The produced films were characterized using an X-ray diffractometer, which showed a reflection from orientation at 111-cubic or (0002)-hexagonal structure of GaN with the quality improved by the higher Ga sputtering voltage.