Role of local structure in the optical and electronic properties of oxygen vacancies in different crystal phases of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>Ga</mml:mi> <mml:mn>2</mml:mn> </mml:msub> <mml:msub> <mml:mi mathvariant="normal">O</mml:mi> <mml:mn>3</mml:mn> </mml:msub> </mml:mrow> </mml:math>

Abstract

We investigate the structural, electronic, and optical properties of oxygen vacancies ( <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:msub> <a:mi mathvariant="normal">V</a:mi> <a:mi mathvariant="normal">O</a:mi> </a:msub> </a:math> ) in crystalline <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:mi>α</d:mi> <d:mo>,</d:mo> <d:mo> </d:mo> <d:mi>β</d:mi> </d:math> , and <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"> <e:mrow> <e:mi>ε</e:mi> <e:mtext>−</e:mtext> <e:msub> <e:mi>Ga</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> using density functional theory (DFT) calculations with the PBE0-TC-LRC functional. Our results reveal that the charge transition levels (CTLs) associated with <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"> <g:msub> <g:mi mathvariant="normal">V</g:mi> <g:mi mathvariant="normal">O</g:mi> </g:msub> </g:math> exhibit significant variations depending on the crystal phase and the coordination environment of surrounding atoms. In particular, <j:math xmlns:j="http://www.w3.org/1998/Math/MathML"> <j:mrow> <j:msub> <j:mi mathvariant="normal">V</j:mi> <j:mi mathvariant="normal">O</j:mi> </j:msub> <j:mi mathvariant="normal">s</j:mi> </j:mrow> </j:math> surrounded by tetrahedral Ga atoms ( <n:math xmlns:n="http://www.w3.org/1998/Math/MathML"> <n:mrow> <n:mi>T</n:mi> <n:mtext>-Ga</n:mtext> </n:mrow> </n:math> ) exhibit deeper CTLs compared to those surrounded by octahedral Ga atoms ( <o:math xmlns:o="http://www.w3.org/1998/Math/MathML"> <o:mrow> <o:mi>O</o:mi> <o:mtext>-Ga</o:mtext> </o:mrow> </o:math> ). We also observe distinct atomic relaxations, with larger displacements of <p:math xmlns:p="http://www.w3.org/1998/Math/MathML"> <p:mrow> <p:mi>T</p:mi> <p:mtext>-Ga</p:mtext> </p:mrow> </p:math> atoms compared to <q:math xmlns:q="http://www.w3.org/1998/Math/MathML"> <q:mrow> <q:mi>O</q:mi> <q:mtext>-Ga</q:mtext> </q:mrow> </q:math> atoms in the vicinity of <r:math xmlns:r="http://www.w3.org/1998/Math/MathML"> <r:mrow> <r:msub> <r:mi mathvariant="normal">V</r:mi> <r:mi mathvariant="normal">O</r:mi> </r:msub> <r:mi mathvariant="normal">s</r:mi> </r:mrow> </r:math> . Using linear-response time-dependent DFT, we investigate the optical transitions of <v:math xmlns:v="http://www.w3.org/1998/Math/MathML"> <v:msub> <v:mi mathvariant="normal">V</v:mi> <v:mi mathvariant="normal">O</v:mi> </v:msub> </v:math> and identify two distinct types of transitions: defect state to conduction band state and valence band to defect state. These results can be used to better understand the optical properties of <y:math xmlns:y="http://www.w3.org/1998/Math/MathML"> <y:msub> <y:mi mathvariant="normal">V</y:mi> <y:mi mathvariant="normal">O</y:mi> </y:msub> </y:math> defects in <bb:math xmlns:bb="http://www.w3.org/1998/Math/MathML"> <bb:mrow> <bb:msub> <bb:mi>Ga</bb:mi> <bb:mn>2</bb:mn> </bb:msub> <bb:msub> <bb:mi mathvariant="normal">O</bb:mi> <bb:mn>3</bb:mn> </bb:msub> </bb:mrow> </bb:math> films. Published by the American Physical Society 2024

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