Fabrication of p+ contact by thermally induced solid state regrowth of Al on p-type Ge crystal

TL;DR

This study demonstrates a method to create p+ contacts on germanium by thermally annealing aluminum, leading to inter-diffusion and doping effects confirmed through SIMS and Hall measurements.

Contribution

It introduces a thermal annealing process for Al on Ge to achieve solid-state regrowth of p+ contacts, with detailed analysis of diffusion and doping profiles.

Findings

Al diffuses into Ge during annealing, forming a p+ region.

Al impurity induces p+ doping with concentration decreasing into Ge.

Surface sheet resistance varies with Al layer thickness.

Abstract

Formation of p+ contact on Germanium is important for applications in diode detector and other electronic devices. In this work, thermally deposited Al on Ge crystal is annealed at 350oC followed by slow cooling for solid-state regrowth of Al-Ge p+ contact on Ge. Depth profile analysis by secondary ion mass spectrometry (SIMS) is carried out to investigate the occurrence of Al and Ge along the depth of the regrown Al-Ge layer. Evidence of regrowth is observed due to inter-diffusion of both Ge and Al across the layers although Ge diffusion in Al layer is found to be more prevalent. Thickness of the evaporated Al layer is varied to understand the diffusion profile of Al, Ge and estimate the depth of Al incorporation in Ge crystal underneath. Hall measurement at different depth of Al-Ge regrown layer reveals that Al impurity induces p+ doping in p-type Ge and its concentration gradually reduces towards the Ge crystal. Top surface of the Al-Ge layer exhibits lowest sheet resistance that varies with the thickness of the as deposited Al layer.