Effect of the amorphous germanium film thickness on the process of gold-induced crystallization

Results of an experimental study of gold-induced crystallization of thin films of amorphous germanium (a-Ge) are reported. The Raman spectroscopy and optical microscopy are applied to study the influence of the initial thickness of the a-Ge film on the morphology of the material obtained by means of annealing of bilayer Au/a-Ge structures. The a-Ge/Au thickness ratios equal to 1.1 and 2.3 are considered. Low-temperature annealing of quartz/Au/a-Ge samples is performed in a high-vacuum atmosphere (10−4 Pa) at a temperature of 300°C for 24 h. The Raman spectroscopy results show that sample annealing leads to complete crystallization of a-Ge with formation of polycrystalline germanium (poly-Ge) in both bottom and upper layers of the samples. For the sample with a-Ge/Au = 2.3, a continuous poly-Ge film is obtained on the substrate due to implementation of the layer exchange mechanism. In this case, poly-Ge hillocks are formed in the upper layer of the sample due to a-Ge crystallization in the presence of Au. For the sample with a-Ge/Au = 1.1, a non-continuous poly-Ge film with a coverage degree of 30 % is formed in the bottom layer. The poly-Ge material is formed in the upper layer due to the processes of “explosive” crystallization and secondary crystallization induced by Au.