Effects of P, As, and Sb heavy doping on band gap narrowing of germanium as light-emitting materials

TL;DR

This study uses first-principles calculations to analyze how P, As, and Sb doping narrows the band gap of germanium, enhancing its potential as a light-emitting material by revealing the underlying electronic and structural mechanisms.

Contribution

It provides a detailed theoretical analysis of how specific n-type dopants induce band gap narrowing in germanium, correlating impurity states and lattice distortion with experimental photoluminescence shifts.

Findings

Doping induces both indirect and direct band gap narrowing.

Impurity states mainly cause indirect band gap reduction.

Lattice distortion from dopants leads to direct band gap narrowing.

Abstract

The n-type tensile-strained Ge can be used as high-efficient light-emitting materials. To reveal the influence of n-type doping on the electronic structure of Ge, we have computed the electronic structure of P, As and Sb doped Ge using first-principles calculation and band unfolding technique. We find that these n-type doping can induce both indirect and direct band gap narrowing, which well reproduce experimental observation that red-shifts occur in photoluminescence spectra of Ge with n-type doping. We reveal that the indirect band gap narrowing is mainly caused by impurity state, while the direct band gap narrowing is a result of lattice distortion induced by the dopant atom. Moreover, we find that it can use E_g^{\Gamma}-E_g^L to explain the voltage increase was needed to reach the same current densities of light emission through the different samples with increasing doping concentrations.