Influence of Process Parameters on the RF Sputtered GaP Thin Films

In this work, gallium phosphide thin films were deposited on glass substrates by radio frequency (RF) magnetron sputtering technique under different depositions conditions. The X-ray diffraction analysis showed a diversity of states: from amorphous in the films deposited at 175 °C to a nearly stoichiometric and polycrystalline films, exhibiting cubic phase with preferred orientation along (220), in the films deposited at temperatures higher than 250 °C. Scanning electron microscopy images revealed that all films were uniform with a smooth surface, while the energy-dispersive spectroscopy (EDS) analysis showed that there was a visible dependence on the Ga/P ratio in the deposition conditions and confirmed that a residual Ga metallic phase was presented in the surface of all the films. The Raman analysis showed the structural evolution of the GaP films was strongly dependent on the deposition conditions. The conductivity of the films was slightly dependent on the argon pressure and the rf power, but strongly dependent on the deposition temperature, mainly above 200 °C. The optical transmission and absorption analyses of the GaP films revealed an indirect band gap of ∼1.70 eV in the films deposited at temperatures less than 200 °C, which transited to a band gap of 2.26 eV as the deposition temperature was close to 300 °C.