Dependence of Mg acceptor levels in InN on doping density and temperature

Abstract

Infrared (IR) reflectance and transmission spectra of Mg doped InN films are analyzed using a dielectric function consisting of the terms of phonon, plasmon, and electronic transition between the valence band and the acceptor levels. The reflectance spectra at lower temperatures than 200 K are highly affected by the electronic transition. Acceptor activation energy Ea decreases with the increase in ionized acceptors because of the Coulomb potential overlap of acceptors charged by the background electrons and/or hole generation by the temperature increase. It is found that Ea is 69(±5) meV at low Mg− density limit and decreases to 50 meV at 5 K because of the charging by the background electrons of the density of 1 × 1018 cm−3. Temperature increase causes the further decrease in Ea, which causes the high hole density of the order of 1018 cm−3 at room temperature in spite of the high degeneracy of the acceptor states. The heavy hole mass is obtained as 0.59(±0.06)m0.