Effect of interfaces and thickness on the crystallization kinetics of amorphous germanium films

The processes of crystallization of amorphous germanium films of various thicknesses and multilayer germanium/silicon nanostructures under isothermal annealing ($T$ = 440$^\circ$C) were studied. Samples were grown on glass substrates using the method of plasma-chemical deposition. The phase composition of the structures was determined from the analysis of Raman spectra. It was found that 200 nm thick germanium film almost completely crystallizes after two hours of annealing, while crystalline nuclei with a volume fraction of less than 1% only appear in a 6 mm thick germanium film. Four-hour annealing of a thin film leads to a noticeable increase in the nuclei size and the crystallinity fraction increases to 40%. Annealing of $\alpha$-Ge (6nm) nanolayers embedded in $\alpha$-Si matrix under the same conditions for 2 and 4 hours does not even lead to partial crystallization, the layers remain amorphous. The influence of interfaces on the crystallization of germanium layers is discussed.