Morphology of Ge thin films crystallized by Au-induced layer exchange at low temperature (220 °C)

The influence of the original amorphous Ge (a-Ge) layer thickness on the crystallization behavior by Au-induced crystallization at low temperature (220 °C) is studied. Initially, the coverage of the crystalline Ge (c-Ge) layer increases as the a-Ge layer thickness increases. A further increase in a-Ge layer thickness, however, results in the decrease of the coverage and appearance of the second Ge layer on top of the first layer, which results in the increase of surface roughness. The bottom c-Ge layer has a better crystal quality compared to the top layer. The maximum coverage of ∼97% with only a small amount of second layer is obtained by annealing an a-Ge(46 nm)/Au(29 nm) bilayer and a Hall effect hole mobility of as high as ∼85 cm2/V s is achieved.