Influence of interface potential on the effective mass in Ge nanostructures

TL;DR

This paper introduces a new theoretical approach to understanding how interface potential affects the effective mass of charge carriers in germanium nanostructures, supported by experimental comparisons of different fabrication methods.

Contribution

A novel formalism relating spatially dependent effective mass to interface potential, applied to Ge quantum dots from different fabrication techniques.

Findings

Higher interface potential reduces effective mass in PECVD QDs

Oxygen interface states can suppress interface potential effects

The influence of interface potential extends over a specific length scale

Abstract

The role of the interface potential on the effective mass of charge carriers is elucidated in this work. We develop a new theoretical formalism using a spatially dependent effective mass that is related to the magnitude of the interface potential. Using this formalism we studied Ge quantum dots (QDs) formed by plasma enhanced chemical vapour deposition (PECVD) and co-sputtering (sputter). These samples allowed us to isolate important consequences arising from differences in the interface potential. We found that for a higher interface potential, as in the case of PECVD QDs, there is a larger reduction in the effective mass, which increases the confinement energy with respect to the sputter sample. We further understood the action of O interface states by comparing our results with Ge QDs grown by molecular beam epitaxy. It is found that the O states can suppress the influence of the interface potential. From our theoretical formalism we determine the length scale over which the interface potential influences the effective mass.