AVS 53rd International Symposium
    Thin Film Thursday Sessions
       Session TF-ThM

Paper TF-ThM6
Formation of c-Si/a-Si:H Interfaces Studied by Real-Time Second-Harmonic Generation, Spectroscopic Ellipsometry, and Infrared Spectroscopy

Thursday, November 16, 2006, 9:40 am, Room 2022

Session: Fundamentals in Thin Film Deposition
Presenter: J.J.H. Gielis, Eindhoven University of Technology, The Netherlands
Authors: J.J.H. Gielis, Eindhoven University of Technology, The Netherlands
P.J. van den Oever, Eindhoven University of Technology, The Netherlands
B. Hoex, Eindhoven University of Technology, The Netherlands
M.C.M. Van De Sanden, Eindhoven University of Technology, The Netherlands
W.M.M. Kessels, Eindhoven University of Technology, The Netherlands
Correspondent: Click to Email
The properties of crystalline silicon / amorphous silicon (c-Si/a-Si:H) interfaces are of key importance for new developments in solar cell research, e.g. to obtain high efficiency silicon heterojunction (SHJ) solar cells or diffused emitter solar cells with an excellent level of surface passivation. We have studied the interface formation between H-terminated Si(100) and a-Si:H in a hot-wire chemical vapor deposition process (HWCVD). The interface formation has been studied in real-time for films between 5 and 70 nm using three different optical diagnostics simultaneously. Spectroscopic ellipsometry (SE) has been used to determine the optical properties of the a-Si:H, the film thickness and the surface roughness evolution and gives insight into the nucleation phase of film growth. Information on the hydrogen bonding modes and hydrogen depth profile in the film has been obtained by attenuated total reflection (ATR) infrared spectroscopy. Second-harmonic generation (SHG), a nonlinear optical technique sensitive to surface and interface states, has been used both in real-time and spectroscopically in the fundamental photon energy range of 1.33-1.75 eV. In this range the SHG signal is governed by two-photon resonances related to modified Si-Si bonds in the surface and interface regions of the c-Si and a-Si:H. The spectral width of the resonances provides a distinction between c-Si and a-Si:H. The spectra indicate that the SHG signal is generated mainly at the c-Si/a-Si:H interface. From the real-time experiments detailed information into the c-Si/a-Si:H interface formation is obtained, such as: the nucleation of a-Si:H islands on the c-Si along with SiH@sub x@ surface species, the occurrence of film 'closure', and the appearance of bulk SiH@sub x@ together with a correlation with the SHG signal. On the basis of these observations key aspects of the c-Si/a-Si:H interface formation will be discussed.