PECVD-growth of GaS1–xSex films with composition-controlled structural, optical and electrical properties

The growth of GaS_1–xSe_x films (0 ≤ x ≤ 1) on a sapphire substrate (001) was achieved through plasma-enhanced chemical vapor deposition, utilizing elemental precursors. The non-equilibrium low-temperature RF discharge plasma was the trigger for the chemical reactions that occurred during the deposition. The reactive components of the plasma formed in the gas phase were studied by means of optical emission spectroscopy. All deposited films were found to have a layered hexagonal structure with preferential orientation (004) and were characterized by linearly increasing lattice parameters with increasing selenium content (x). A shift of the out-of-plane vibration modes was observed in the Raman spectra. The films exhibit high transparency, with values approaching 70%, in the 500-2500 nm region. The samples of GaS_1–xSe_x luminesce from the blue to the red visible region, depending on their composition. It has been demonstrated that the substitution of sulfur for selenium results in a regular shift of the band edge and photoluminescence peaks to the long-wavelength region. The dependences of the surface morphology and conductivity on the composition were non-monotonic. The photosensitivity of the GaS_1-xSe_x films gradually increases with increasing selenium content, and pure gallium selenide has the maximum photoresponse. The comprehensive study of GaS_1-xSe_x films across the full compositional range allows to broadly consider them as a potential candidate for optoelectronic applications.