In situ removal of a native oxide layer from an amorphous silicon surface with a UV laser for subsequent layer growth
We have developed an in situ method for removing a native silicon oxide layer from an amorphous silicon (a-Si) surface using a UV laser. The a-Si film containing crystalline silicon seeds is used for the subsequent growth of crystalline Si layers by steady-state liquid phase epitaxy (SSLPE). The main goal of this technique is to grow crystalline silicon layers on low-cost glass substrates which can be used as absorber layers for thin film solar cells. We have investigated the interaction between a-Si and laser pulses as well as the growth results by scanning force microscopy (SFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR). The heating of the a-Si surface by a laser pulse is modelled by numerical simulations using a finite element approach in COMSOL-Multiphysics. The simulations verify that the laser pulse heats a-Si to temperatures sufficient for the thermal desorption of the native oxide layer but lower than both the crystallization temperature of a-Si and the glass transition temperature.