Compensating defects in Si-doped AlN bulk crystals

The rather low n-type conductivity observed in Si-doped sublimation-grown AlN bulk crystals is explained by the formation of high concentrations of compensating defects. The model is based on the experimental verification of a shallow impurity band formed by Si donors and the presence of acceptor-like electron traps within 1 eV below the conduction band edge. Further it is suggested that the majority of the Si donors is compensated by deep acceptors in the lower half of the band gap. This compensation model is an alternative to the controversially discussed assumption of Si DX center formation.