Effect of composition in Si1−xGex seed layer on the solid phase crystallization of ultrathin amorphous silicon layer

Abstract

The effect of top silicon-germanium (Si1−xGex) layers on the crystallization of underlying amorphous Si (a-Si) films was investigated for various Ge compositions in Si1−xGex. Si and Si1−xGex films were sequentially deposited on thermal SiO2 by using SiH4 and GeH4 source gases in reduced pressure chemical vapor deposition. The fraction and the microstructure of underlying crystallized Si were characterized by plan-view transmission electron microscopy. Scanning nanobeam diffraction was performed to investigate the grain size of crystallized Si films. The crystallization of the underlying a-Si thin film in a-Si1−xGex/Si bilayer stack gradually increased with the increasing Ge composition of the top Si1−xGex layer. The grain size of underlying crystallized Si films showed a dependence on the Ge composition of top Si1−xGex. For Si1−xGex with 22% Ge, microtwins were observed to be the dominant defect, while stacking faults were dominant for Si1−xGex with 47% Ge. The Ge composition and the thickness of Si1−xGex are important factors to obtain the optimized crystallization time and grain size of ultrathin a-Si with a reduced density of intragrain defects.