Acceptor binding energies in GaN and AlN

TL;DR

This study calculates acceptor binding energies in GaN and AlN using effective mass theory, considering various impurities and crystal phases, and compares theoretical results with experimental data.

Contribution

It introduces a detailed theoretical approach for calculating acceptor binding energies in GaN and AlN, including polaron effects and impurity-specific pseudopotentials.

Findings

Good agreement with experimental data for WZ-GaN

ZB-GaN acceptors are predicted to have shallower binding energies

Binding energies in AlN are similar to GaN but depend on band parameters

Abstract

We employ effective mass theory for degenerate hole-bands to calculate the acceptor binding energies for Be, Mg, Zn, Ca, C and Si substitutional acceptors in GaN and AlN. The calculations are performed through the 6$\times $6 Rashba-Sheka-Pikus and the Luttinger-Kohn matrix Hamiltonians for wurtzite (WZ) and zincblende (ZB) crystal phases, respectively. An analytic representation for the acceptor pseudopotential is used to introduce the specific nature of the impurity atoms. The energy shift due to polaron effects is also considered in this approach. The ionization energy estimates are in very good agreement with those reported experimentally in WZ-GaN. The binding energies for ZB-GaN acceptors are all predicted to be shallower than the corresponding impurities in the WZ phase. The binding energy dependence upon the crystal field splitting in WZ-GaN is analyzed. Ionization levels in AlN are found to have similar `shallow' values to those in GaN, but with some important differences, which depend on the band structure parameterizations, especially the value of crystal field splitting used.