Theoretical evidence for the semi-insulating character of AlN

TL;DR

This paper provides theoretical evidence that aluminum nitride (AlN) is inherently semi-insulating due to the deep energy levels of its acceptors and donors, explaining the doping challenges in Al-rich AlGaN alloys.

Contribution

The study offers ab initio calculations showing that acceptors and donors in AlN are deep, supporting its semi-insulating nature and clarifying doping difficulties.

Findings

Acceptors in AlN are deeper than in GaN.

Donors such as Si_Al, C_Al, and V_N are deep levels.

AlN is predicted to be semi-insulating under typical conditions.

Abstract

We present ab initio density-functional calculations for acceptors, donors, and native defects in aluminum nitride, showing that acceptors are deeper (Be ~ 0.25 eV, Mg_ 0.45 eV) and less soluble than in GaN; at further variance with GaN, both the extrinsic donors Si_Al and C_Al, and the native donor V_N (the anion vacancy) are found to be deep (about 1 to 3 eV below the conduction). We thus predict that doped AlN will generally turn out to be semi-insulating in the normally achieved Al-rich conditions, in agreement with the known doping difficulties of high-x AlGaN alloys.