Epitaxial Silicon Thin Films by Low-Temperature Aluminum Induced Crystallization of Amorphous Silicon for Solar Cell Applications

Aluminum-induced crystallization of hydrogenated amorphous silicon was used to fabricate epitaxial silicon films through solid phase epitaxy. Silicon wafers of (100) orientation were used as the starting crystalline structure for the epitaxial thin film growth. A configuration of c-Si/Al/a-Si:H was used to produce these films through the phenomenon of layer inversion. A thin layer of aluminum (300 nm) was deposited on a silicon wafer by sputtering. On top of this layer, a 300 nm amorphous silicon film was deposited using plasma-enhanced chemical vapor deposition. After annealing the samples at 475°C for 40 minutes, a continuous film of crystalline silicon was formed on the silicon substrate. X-ray diffraction, scanning electron microscopy, and cross- sectional transmission electron microscopy were used to characterize the films. Auger depth profiling indicated the formation of a Si/Al mixed phase within the first few minutes of annealing. A proposed model of the growth mechanism is presented.