First-principles calculations on point defects and doping in (Al,Ga)₂O₃ ultrawide-band gap semiconductors

Semiconductor devices utilizing ever-wider band gap materials have the promise of more compact and efficient energy conversion that can help accelerate the transformation to an energy infrastructure based primarily on renewable resources. Gallium oxide and related alloys are rapidly developing as promising material platforms for next-generation power electronics owing to their large, tunable band gaps, controllable electrical conductivity, and commercially-available single-crystal substrates that can be grown via a number of industrially-scalable processes. Analogous to the AlGaN system, the incorporation of Al into Ga₂O₃ to form (Al<i>_x</i>Ga_1-x)₂O₃ (AGO) alloys can lead to a significant increase of the band gap, but spanning a much larger rage of ~4.8 eV-8.6 eV. AGO 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 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 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 conventional dopants such as Si, Ge and Sn, as well as lesser-explored transition-metal donor dopants that have been identified as effective alternatives. We additionally consider the role of native cation vacancies, which are known to be potentially problematic sources of compensation. Our results identify composition regimes in AGO 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/>This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and supported by the LLNL Laboratory Directed Research and Development funding under project number 22-SI-003 and the Critical Materials Institute, an Energy Innovation Hub funded by the U.S. DOE, Office of Energy Efficiency and Renewable Energy, Advanced Materials and Manufacturing Office.