Atomistic Description of Shallow Levels in Semiconductors

TL;DR

This paper uses a tight binding approach to accurately model shallow donor levels in GaAs, revealing a transition from shallow to deep states and comparing results with effective mass theory.

Contribution

It introduces a large-scale tight binding model for shallow levels in semiconductors and compares its predictions with effective mass theory.

Findings

Excellent agreement in binding energies with effective mass theory

Identification of a sharp shallow-deep transition with increasing impurity perturbation

Differences in anisotropies and decay profiles compared to hydrogenlike models

Abstract

The wave function and binding energy for shallow donors in GaAs are calculated within the tight binding (TB) approach, for supercells containing up to two million atoms. The resulting solutions, coupled with a scaling law, allow extrapolation to the bulk limit. A sharp shallow-deep transition is obtained as the impurity perturbation increases. The model allows investigating the quantitative consistency between the effective mass theory and the TB formalism. Although the calculated binding energies are in excellent agreement, anisotropies and the overall decay obtained in the TB envelope function can not be afforded by the hydrogenlike effective mass prediction.