No 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 (10 19 to 10 21 cm −3 ) on highly ordered crystalline Ge films. Here, the deposition temperatures (T d ) 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 outdiffusion that correlated with the diffusion parameters, followed by the reevaporation 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.

To realize nanostructured vertical Ge transistors, we investigated the formation of Sb-doped Ge layers on p-type Ge (100) substrate by molecular beam epitaxy. The effect of dopant source temperature variations during deposition on the crystallinity and electrical properties of epitaxial Ge layers was discussed in detail. The doping at Tdop.: 325-400ºC realizes n-type Ge layers, that indicated by the rectification behavior of the Ge n+/p junction diodes. Moreover, higher Tdop. (~400ºC) resulted in current on-off ratio improvement while maintaining the crystallinity at high dopant concentration.