Solid phase crystallization of amorphous Si1−xGex films deposited on SiO2 by molecular beam epitaxy

Abstract

We have investigated solid phase crystallization behavior of the molecular beam epitaxy grown amorphous Si1−xGex (x=0 to 0.53) alloy layers using x-ray diffractometry and transmission electron microscopy (TEM). Our results show that the thermal budget for the full crystallization of the film is significantly reduced as the Ge concentration in the film is increased. In addition, we find that a pure amorphous Si film crystallizes with a strong (111) texture while that of the Si1−xGex alloy film crystallizes with a (311) texture suggesting that the solid phase crystallization mechanism is changed by the incorporation of Ge. TEM analysis of the crystallized film shows that the grain morphology of the pure Si is an elliptical and/or a dendrite shape with a high density of microtwins in the grains while that of the Si0.47Ge0.53 alloy is more or less equiaxed shape with a much lower density of defects. From these results, we conclude that the crystallization mechanism changes from a twin-assisted growth mode to a random growth mode as the Ge concentration in the film is increased.