Defects and doping in ultra-wide band gap (Al,Ga)N and β-(Al,Ga)₂O₃ alloys

Si is the n-type dopant of choice for GaN and β-Ga₂O₃. However, in (Al,Ga)N and β-(Al,Ga)₂O₃ alloys, when the Al content is increased, the n-type conductivity produced by the added Si impurities is efficiently compensated. The experimentally determined critical Al fractions are about 70% for the (Al,Ga)N alloys and as low as 25% for the β-(Al,Ga)₂O₃ alloys. AlN and Al₂O₃ are well known to be poorly n-type dopable even with Si, but the detailed compensation mechanisms in the alloys are not necessarily the same as in the compounds. This short review discusses recent research in Si-doped (Al,Ga)N and β-(Al,Ga)₂O₃ alloys in the light of the compensation phenomena caused by Si DX center and cation vacancy formation.