An efficient direct band-gap transition in germanium by three-dimensional strain

TL;DR

This study demonstrates that applying a small isotropic 3D tensile strain to germanium can induce a direct band gap, significantly enhancing its optical and electronic properties, which is promising for advanced semiconductor applications.

Contribution

The paper introduces a computational approach to identify strain conditions that transform germanium into a direct band-gap semiconductor without doping.

Findings

Direct band gap achieved at 0.34% triaxial tensile strain

Significant increase in refractive index and electron mobility

Potential for optimizing semiconductor properties through 3D strain

Abstract

Complementary to the development of highly three-dimensional (3D) integrated circuits in the continuation of Moore's law, there has been a growing interest in new 3D deformation strategies to improve device performance. To continue this search for new 3D deformation techniques, it is essential to explore beforehand - using computational predictive methods - which strain tensor leads to the desired properties. In this work, we study germanium (Ge) under an isotropic 3D strain on the basis of first-principle methods. The transport and optical properties are studied by a fully ab initio Boltzmann transport equation and many-body Bethe-Salpeter equation (BSE) approach, respectively. Our findings show that a direct band gap in Ge could be realized with only 0.34% triaxial tensile strain (negative pressure) and without the challenges associated with Sn doping. At the same time a significant increase in refractive index and carrier mobility - particularly for electrons - is observed. These results demonstrate that there is a huge potential in exploring the 3D deformation space for semiconductors - and potentially many other materials - in order to optimize their properties.