Dopant Redistribution in High-Temperature-Grown Sb-Doped Ge Epitaxial Films

Abstract

Heavily doped n-type Ge crystals are essential for Ge-based electronics and optical applications. In this report, we describe the mechanism of dopant redistribution via out-diffusion and re-evaporation processes in Sb-doped Ge epitaxial films grown by molecular beam epitaxy (MBE). The temperature-modulated depositions yielded a uniformly distributed and high Sb concentration (1019 to 1021 cm–3) on highly ordered crystalline Ge films. Here, the deposition temperatures (Td) control the transition of amorphous to epitaxial growth, as well as the Sb concentration profiles. A significant difference in the dopant levels is attributed to Sb out-diffusion that correlated with the diffusion parameters, followed by the re-evaporation from the Ge crystal in high-temperature conditions. Meanwhile, the substituted Sb atoms act as donors that form the n-type Ge film. This understanding of dopant behavior in the epitaxially grown Ge film opens a path to achieve well-defined n+-Ge thin films for Ge-based devices with improved electrical properties.