Low-temperature growth of polycrystalline Ge thin film on glass by in situ deposition and ex situ solid-phase crystallization for photovoltaic applications

Poly-crystalline germanium (poly-Ge) thin films have potential for lowering the manufacturing cost of photovoltaic devices especially in tandem solar cells, but high crystalline quality would be required. This work investigates the crystallinity of sputtered Ge thin films on glass prepared by in situ growth and ex situ solid-phase crystallization (SPC). Structural properties of the films were characterized by Raman, Xray diffraction and ultraviolet-visible reflectance measurements. The results show the transition temperature from amorphous to polycrystalline is between 255 degrees C and 280 degrees C for in situ grown poly-Ge films, whereas the transition temperature is between 400 degrees C and 500 degrees C for films produced by SPC for a 20 h annealing time. The in situ growth in situ crystallized poly-Ge films at 450 degrees C exhibit significantly better crystalline quality than those formed by solid-phase crystallization at 600 degrees C. High crystalline quality at low substrate temperature obtained in this work suggests the poly-Ge films could be promising for use in thin film solar cells on glass. (c) 2009 Elsevier B.V. All rights reserved.