Study Of Si-Ge Interdiffusion With a High Phosphorus Doping Concentration

TL;DR

This study investigates how high phosphorus doping accelerates Si-Ge interdiffusion in layered structures, using experiments and modeling to understand the underlying mechanisms and implications for device fabrication.

Contribution

It provides experimental data and a Fermi-enhancement model showing doping-dependent interdiffusion behavior in high Ge content Si-Ge structures.

Findings

Doped samples show 2-8 times faster interdiffusion than undoped.

Interdiffusion coefficient proportional to n^2/n_i^2, indicating defect involvement.

Fermi-enhancement factor weakly depends on temperature and Ge fraction.

Abstract

Si-Ge interdiffusion with a high phosphorus doping level was investigated by both experiments and modeling. Ge/Si1-xGex/Ge multi-layer structures with 0.75<x_Ge<1 , a mid-10^18 to low-10^19 cm-3 P doping and a dislocation density of 10^8 to 10^9 cm-2 range were studied. The P-doped sample shows an accelerated Si-Ge interdiffusivity, which is 2-8 times of that of the undoped sample. The doping dependence of the Si-Ge interdiffusion was modelled by a Fermi-enhancement factor. The results show that Si-Ge interdiffusion coefficient is proportional to n^2/n_i^2 for the conditions studied, which indicates that the interdiffusion in high Ge fraction range with n-type doping is dominated by V^(2-) defects. The Fermi-enhancement factor was shown to have a relatively weak dependence on the temperature and the Ge fraction. The results are relevant to structure and thermal processing condition design of n-type doped Ge/Si and Ge/SiGe based devices such as Ge/Si lasers.