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

Nano-crystalline Ge x C 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 x C 1 − x in large areas by an industry-friendly process can enhance its scope as a photovoltaic absorber. In this work nano-crystalline Ge x C 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 x C 1 − x crystals were scattered in the film with d-spacing of 3.4 nm between the fringes (calculated a = 5.53 A), 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 x C 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 x C 1 − x is found in the film deposited at 350 °C using XPS fitting.