Synthesis of nano-crystalline germanium carbide using radio frequency magnetron sputtering

Nano-crystalline Ge_xC_{1 - x} is a potential third generation solar cell absorber material due to its favourable opto-electronic properties and relatively high abundance of elements. The ability to grow nano-crystalline Ge_xC_{1 - x} in large areas by an industry-friendly process can enhance its scope as a photovoltaic absorber. In this work nano-crystalline Ge_xC_{1 - x} thin films have been grown on Si (100) substrate using radio frequency magnetron sputtering. The crystallinity, composition, structure and optical properties of the films were determined by, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, atomic force microscopy, transmission electron microscopy (TEM) and ultra-violet visible infrared spectroscopy. From TEM results it was found that Ge_xC_{1 - x} crystals were scattered in the film with d-spacing of 3.4 nm between the fringes (calculated a = 5.53 Å), but that a small number of nanoparticles of GeC were present. The Raman signature of the local Ge-C mode is identified near 530 cm^{- 1} in Ge_xC_{1 - x} film grown at 350°C. The band gap energy value was estimated to be 0.90 eV from optical reflectance spectra. Maximum 15.5% of Ge_xC_{1 - x} is found in the film deposited at 350°C using XPS fitting.