The effect of valley-spin degeneracy on the screening of charged impurity centers in two- and three-dimensional electronic devices

TL;DR

This paper investigates how valley-spin degeneracy influences the screening and binding energies of charged impurities in 2D and 3D electronic systems, highlighting significant dependence on degeneracy levels and screening effects.

Contribution

It provides a detailed analysis of valley-spin degeneracy effects on impurity screening using the STLS method, including bound state wave functions and Friedel oscillations.

Findings

Valley-spin degeneracy significantly affects impurity binding energies.

Friedel oscillations are prominent in two-dimensional systems.

Screening effects vary with degeneracy and density.

Abstract

Accurate characterization of charged impurity centers is of importance for the electronic devices and materials. The role of valley-spin degeneracy on the screening of an attractive ion by the mobile carriers is assessed within a range of systems from spin-polarized single-valley to six-valley. The screening is treated using the self-consistent local-field correction of Singwi and co-workers known as STLS. The bound electron wave function is formulated in the form of an integral equation. Friedel oscillations are seen to be influential especially in two-dimensions which cannot be adequately accounted for by the hydrogenic variational approaches. Our results show appreciable differences at certain densities with respect to simplified techniques, resulting mainly in the enhancement of the impurity binding energies. The calculated Mott constants are provided where available. The main conclusion of the paper is the substantial dependence of the charged impurity binding energy on the valley-spin degeneracy in the presence of screening.