Insights for Achieving High Conductivities in Ga₂O₃ and (Al,Ga)₂O₃ Alloys Using Hybrid Functional Calculations

Gallium oxide continues to rapidly develop as a candidate for next-generation power electronics owing to its large band gap, controllable conductivity and the availability of large single-crystal substrates grown from the melt. Of significant interest is the formation of alloys with Al to form (Al<i>_x</i>Ga_1-x)₂O₃ (AlGO), which lead to a significant increase of the band gap analogous to the AlGaN system, but spanning a much larger rage of ~4.8 eV-8.6 eV. AlGO also exhibits the possibility of different crystal structures and lattice constants, leading to a number of possible epitaxial relationships beyond the wurtzite AlGaN system. Despite this promise, a number of questions remain as to the effectiveness of controllable donor doping and how to overcome the possibility of compensation in the limit high Al-contents, similar to that in AlGaN. Here we assess <i>n</i>-type doping of Ga₂O₃ in different polymorphs and consider the prospects of doping in the larger-gap Al-containing alloys using first-principles modelling approaches based on hybrid functional calculations. We consider a number of dopants such as the typical group-IV elements, as well as lesser-explored transition-metal donor dopants that have been identified as effective alternatives. We also discuss the role of cation vacancies in the different polymorphs, which are known to be potentially problematic sources of compensation for <i>n</i>-type doping. Our results identify composition regimes in AlGO alloys that may be most effectively targeted for increased band gaps and effective donor doping, with composition regimes specific to particular dopant species. These results provide guidance for doping in Ga₂O₃ and related alloys incorporated into heterostructure devices.<br/><br/>This work was partially performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and partially supported by LLNL LDRD funding under Project No. 22-SI-003 and by the Critical Materials Institute, an Energy Innovation Hub funded by the U.S. DOE, Office of Energy Efficiency and Renewable Energy, Advanced Materials & Manufacturing Technologies Office.