Tailoring the electronic properties of monoclinic <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mo>(</mml:mo> <mml:msub> <mml:mi>In</mml:mi> <mml:mi>x</mml:mi> </mml:msub> <mml:msub> <mml:mi>Al</mml:m

Ultrawide bandgap semiconductors such as <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:mi>β</a:mi> <a:mtext>−</a:mtext> <a:msub> <a:mi>Ga</a:mi> <a:mn>2</a:mn> </a:msub> <a:msub> <a:mi mathvariant="normal">O</a:mi> <a:mn>3</a:mn> </a:msub> </a:mrow> </a:math> are ideal materials for next-generation power electronic devices. Electronic and mechanical properties of <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mrow> <c:mi>β</c:mi> <c:mtext>−</c:mtext> <c:msub> <c:mi>Ga</c:mi> <c:mn>2</c:mn> </c:msub> <c:msub> <c:mi mathvariant="normal">O</c:mi> <c:mn>3</c:mn> </c:msub> </c:mrow> </c:math> can be tuned by alloying with other sesquioxides, notably <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"> <e:mrow> <e:msub> <e:mi>Al</e:mi> <e:mn>2</e:mn> </e:msub> <e:msub> <e:mi mathvariant="normal">O</e:mi> <e:mn>3</e:mn> </e:msub> </e:mrow> </e:math> and <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"> <g:mrow> <g:msub> <g:mi>In</g:mi> <g:mn>2</g:mn> </g:msub> <g:msub> <g:mi mathvariant="normal">O</g:mi> <g:mn>3</g:mn> </g:msub> </g:mrow> </g:math> . Moreover, by tuning the In content of a <i:math xmlns:i="http://www.w3.org/1998/Math/MathML"> <i:mrow> <i:msub> <i:mrow> <i:mo>(</i:mo> <i:msub> <i:mi>In</i:mi> <i:mi>x</i:mi> </i:msub> <i:msub> <i:mi>Al</i:mi> <i:mrow> <i:mn>1</i:mn> <i:mo>−</i:mo> <i:mi>x</i:mi> </i:mrow> </i:msub> <i:mo>)</i:mo> </i:mrow> <i:mn>2</i:mn> </i:msub> <i:msub> <i:mi mathvariant="normal">O</i:mi> <i:mn>3</i:mn> </i:msub> </i:mrow> </i:math> alloy, its lattice constants can be matched to those of <k:math xmlns:k="http://www.w3.org/1998/Math/MathML"> <k:mrow> <k:msub> <k:mi>Ga</k:mi> <k:mn>2</k:mn> </k:msub> <k:msub> <k:mi mathvariant="normal">O</k:mi> <k:mn>3</k:mn> </k:msub> </k:mrow> </k:math> , while preserving a large conduction-band offset. In view of potential applications to <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"> <m:mrow> <m:mi>β</m:mi> <m:mtext>−</m:mtext> <m:msub> <m:mi>Ga</m:mi> <m:mn>2</m:mn> </m:msub> <m:msub> <m:mi mathvariant="normal">O</m:mi> <m:mn>3</m:mn> </m:msub> </m:mrow> </m:math> -based heterostructure, we performed atomistic modeling of <o:math xmlns:o="http://www.w3.org/1998/Math/MathML"> <o:mrow> <o:msub> <o:mrow> <o:mo>(</o:mo> <o:msub> <o:mi>In</o:mi> <o:mi>x</o:mi> </o:msub> <o:msub> <o:mi>Al</o:mi> <o:mrow> <o:mn>1</o:mn> <o:mo>−</o:mo> <o:mi>x</o:mi> </o:mrow> </o:msub> <o:mo>)</o:mo> </o:mrow> <o:mn>2</o:mn> </o:msub> <o:msub> <o:mi mathvariant="normal">O</o:mi> <o:mn>3</o:mn> </o:msub> </o:mrow> </o:math> alloys using density functional theory to investigate thermodynamic and electrical properties of conventional group IV dopants (Si, Sn, C, Ge), alternative metal donors (Ta, Zr, Hf), and acceptors (Mg, Zn, Cu). The hybrid Heyd–Scuseria–Ernzerhof functional (HSE06) is used to accurately quantify the defect formation energies, ionization levels, and concentrations over a wide range of experimentally relevant conditions for the oxygen chemical potential and temperature. In our atomistic models, Hf and Zr show favorable properties as alternative donors to Si and other group IV impurities, especially under oxygen-poor conditions. Our findings also suggest that acceptors Mg, Zn, and Cu, while they cannot promote <q:math xmlns:q="http://www.w3.org/1998/Math/MathML"> <q:mi>p</q:mi> </q:math> doping, can be still beneficial for the compensation of unintentionally <r:math xmlns:r="http://www.w3.org/1998/Math/MathML"> <r:mi>n</r:mi> </r:math> -doped materials, e.g., to generate semi-insulating layers and improve rectification.