Impacts of Doping on Epitaxial Germanium Thin Film Quality and Si-Ge Interdiffusion

TL;DR

This study investigates how different dopants affect the quality and interdiffusion behavior of epitaxial germanium films on silicon, providing insights for optimizing Ge-on-Si device fabrication.

Contribution

It introduces a comprehensive experimental and theoretical analysis of doping effects on Ge film quality and Si-Ge interdiffusion, including a new quantitative diffusion model.

Findings

B doping increases threading dislocations in Ge films.

P and As doping reduce dislocation density significantly.

A new model describes Si-Ge interdiffusion with dislocation effects.

Abstract

Ge-on-Si structures with three different dopants (P, As and B) and those without intentional doping were grown and annealed. Several different materials characterization methods have been performed to characterize the Ge film quality. All samples have a smooth surface (roughness < 1.5 nm), and the Ge films are almost entirely relaxed. On the other hand, B doped Ge films have threading dislocations above 1 x 10^8 cm-2. While P and As doping can reduce the threading dislocation density to be less than 10^6 cm-2 without annealing. The interdiffusion of Si and Ge of different films have been investigated experimentally and theoretically. A quantitative model of Si-Ge interdiffusion under extrinsic conditions across the full x_Ge range and with the dislocation mediated diffusion term was established. The Kirkendall effect has been observed. The results are of technical significance for the structure, doping, and process design of Ge-on-Si based devices, especially for photonic applications.