Low-temperature plasma deposition of diamond-like carbon (DLC) and gallium nitride thin-films grown on Si substrate by PECVD was investigated using atomic force microscopy and reflectance spectra for photovoltaic devices application. It was found that the morphological features of the GaN film depend on the substrates under the optimum deposition conditions. The optical band gap of the films was approximately 5.5eV for PECVD DLC and approximately 3.3 eV for PECVD GaN.