Electronic behavior of rare-earth dopants in AlN: A density-functional study

Abstract

Local density functional calculations are carried out on Er, Eu, and Tm rare-earth (RE) dopants in hexagonal AlN. We find that the isolated impurities prefer to substitute for Al and, in contrast with isolated RE dopants in GaAs and GaN, ${\mathrm{RE}}_{\mathrm{Al}}$ defects are electrically active and introduce deep donor levels around ${E}_{v}+0.5\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. RE complexes with oxygen and vacancies are discussed; some of these have deep levels in the upper third of the gap and could account for a threshold excitation energy around $4\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ observed for intra-$f$ transitions at 465 and $478\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ in AlN:Tm.