Effect of substrate temperature on microstructure and optical properties of hydrogenated nanocrystalline Si thin films grown by plasma enhanced chemical vapor deposition

In this paper is presented the effect of substrate temperature (T-s.) on the chemical composition, the morphology, the reflectivity and the carrier life time of hydrogenated nanocrystalline silicon (nc-Si:H) thin films, grown by radio frequency Plasma Enhanced Chemical Vapor Deposition (PECVD) on silicon single crystal (1 0 0) using a gas mixture of silane (SiH4) and hydrogen (H-2). Substrate temperature was varied from room temperature to 450 degrees C. Characterization of these films by X-ray diffraction (XRD) and Raman spectroscopy revealed that the crystallite size and at the same time the volume fraction of crystallites in the films tends to decrease with increasing Ts. The Fourier transform infrared spectroscopic analysis (FTIR) showed at low temperature the hydrogen is incorporated in the nc-Si:H films in the mono-hydrogen (Si H) bonding configuration. With increasing Ts the hydrogen bonding in nc-Si:H films shifts from mono-hydrogen (Si-H) to di-hydrogen (Si-H-2) and (Si-H-2)(n). The hydrogen content in the nc-Si:H films decreases with the increase of T-s. From the Atomic Force Microscopy (AFM), it was shown that the increase of T-s tends to increase the porosity and decrease the crystalline grain size. In order to more understand the effect of Ts on this structural change, minority carrier lifetime (MCL) measurement show that only the films with a nanocrystalline silicon structure present an enhancement in MCL which could be related to a quantum size effect and to the SiH-related bonds. (C) 2014 Elsevier Ltd. All rights reserved.