Chapter 2 - Dopants in GaN

Abstract

This chapter describes the state-of-the-art undoped and doped GaN by comparing optical and electronic properties. It shows that N-type doping of GaN using Si is well-understood as Si readily incorporates on a Ga-site forming a single shallow donor with an activation energy of 12–15 meV leading to almost complete donor ionization at room temperature. The growth is controlled over a wide range of densities from low-1017 to mid-1019cm–3, even though some structural problems occur in thick and heavily doped films. While p-type doping remains a major challenge as Mg forms a quasi-shallow acceptor level located more than 170 meV above the valence band edge. The deep nature of the acceptor level leads to poor acceptor ionization of several percent at room temperature. Thus, excessively high Mg concentrations are needed to produce p-type films above mid-1017 cm–3 often resulting in resistive films. The near-band edge optical transitions are well understood in GaN and thus, low temperature photoluminescence spectroscopy is a valuable tool in characterizing nominally undoped GaN.