Approach to achieving a p-type transparent conducting oxide: Doping of bismuth-alloyed Ga2O3 with a strongly correlated band edge state

P-type doping in oxides is usually difficult due to their low valence-band energy. In order to make them p type, the electronic structure of the oxides should be fundamentally changed; that is, the occupied valence band should be raised significantly. Here, using first-principles calculations, we propose that by adding a small amount of Bi2O3 into Ga2O3 to form dilute (BixGa1-x)(2)O-3 alloys and, more importantly, with properly chosen dopants, we can achieve efficient p-type doping in a transparent oxide. We show that adding a few percent of Bi to Ga2O3 leads to an intermediate valence band that is sufficiently high in energy to facilitate p-type doping; however, the commonly expected shallow acceptors, Mg and Zn substitution on the Ga site (Mg-Ga and Zn-Ga), are still deep acceptors, whereas the expected deep acceptor, Cu-Ga, actually creates a relatively shallow level in (BixGa1-x)(2)O-3 alloys. This trend is opposite to what is found in pure Ga2O3. The puzzling behavior of the acceptor levels in the (BixGa1-x)(2)O-3 alloys is attributed to the polaronic character of the holes in the Zn- and Mg-doped cases, and the decoupling of the hole state and the valence-band edge in the Cu-doped case. This understanding provides insights into the realization of p-type doping in dilute (BixGa1-x)(2)O-3 alloys and paves a way to dope semiconductor materials with a strongly correlated band edge state, i.e., materials with a tendency to form polaronic acceptor or donor states.

Automated summary

This study proposes efficient p-type doping in transparent oxides by adding a small amount of Bi2O3 into Ga2O3 to form dilute (BixGa1-x)(2)O-3 alloys. The addition of Bi raises the intermediate valence band energy, facilitating p-type doping, with commonly expected shallow acceptors showing deeper levels in the alloy. This understanding provides insights into doping semiconductor materials with a strongly correlated band edge state.