Al-induced crystallization of amorphous SixGe1-x (0 ⩽ x ⩽ 1): Diffusion, phase development and layer exchange

Al-induced crystallization (AIC) of amorphous SixGe1−x (a-SixGe1−x) solid solutions, with compositions over the entire range of the isomorphous Si-Ge system, was investigated. The crystallization progress was monitored in detail, at low temperatures from 150 to 400°C, by in situ X-ray diffraction while gradually increasing the annealing temperature until crystallization was completed, allowing for an evaluation of the crystallization kinetics. The formation of single-phase crystalline SixGe1−x solid solutions upon AIC of a-SixGe1−x (0 ⩽ x ⩽ 1) was observed at all annealing temperatures. Concentration-depth profiling by Auger electron spectroscopy provided a detailed insight into the diffusion processes occurring in the early stage of the low-temperature AIC process and the intriguing phenomenon of layer exchange of the Al and a-SixGe1−x sublayers. On the basis of evaluation of the Si and Ge diffusion coefficients, the results suggest that, upon AIC, both Si and Ge atoms diffuse at comparable rates into the Al layer in the low temperature range investigated. The degree of completeness of the layer-exchange process after full crystallization is a function of the a-SixGe1−x composition; complete layer exchange occurs for all Al/a-SixGe1−x specimens containing more than 27 at.% Si.