Quantum Size Effects of a-Si(:H)/a-SiC(:H) Multilayer Films Prepared by rf Sputtering

Abstract

Quantum size effects of amorphous silicon/amorphous silicon carbide (a-Si(:H)/a-SiC(:H)) multilayer films prepared by a dual rf magnetron sputtering method are investigated by measurements of Vacuum Ultraviolet Photoelectron Spectroscopy (UPS) and optical absorption. Valence band offsets of a-Si/a-SiC and a-Si:H/a-SiC:H heterojunctions are 0.3 and 0.05 eV, respectively. Optical gaps of a-Si, a-SiC, a-Si:H and a-SiC:H are 1.22, 1.52, 1.87 and 2.20 eV, respectively. In a-Si:H/aSiC:H multilayer film the quantum well layer thickness dependence of the optical gap is found to be in good agreement with a 1-dimensional quantum well model. It is obtained that the effective mass of electron in a-Si:H film is 0.15 m_o (m_o; the mass of free electron). In a-Si/a-SiC multilayer film quantum size effect does not appear. It can be considered that the effective mass of hole in a-Si film is more than hundred times as large as that of free electron.