Defects and doping in (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 the n-type conductivity produced by the added Si impurities is efficiently compensated. The critical Al fractions are about 70% for the (Al,Ga)N alloys and as low as 30% 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.

Positron annihilation spectroscopy is a useful method for studying neutral and negatively charged vacancy-type defects, as well as negatively charged defects with no open volume such as acceptor impurities [1]. I will discuss the most recent results obtained in Si-doped (Al,Ga)N and β-(Al,Ga)₂O₃ alloys in the light of the compensation phenomena caused by cation vacancies, carbon impurities and Si DX center formation. The local environment of the Si dopants appears to have a strong impact on the doping efficiency.

[1] F. Tuomisto and I. Makkonen, Rev. Mod. Phys. 85, 1583 (2013).