Impact of c- and m- sapphire plane orientations on the structural and electrical properties of β-Ga₂O₃ thin films grown by metal-organic chemical vapor deposition

Abstract This work presents a comprehensive investigation into the structural and electrical properties of Ga 2 O 3 thin films grown via metal-organic chemical vapor deposition on both c - and m -plane sapphire substrates. Structural characterization revealed the β -Ga 2 O 3 phase formation in both substrate orientations, with strong epitaxial <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mrow> <mml:mover> <mml:mn>2</mml:mn> <mml:mo stretchy="false">¯</mml:mo> </mml:mover> </mml:mrow> <mml:mn>01</mml:mn> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:math> preferential growth on c -plane substrates and polycrystalline films on m -plane substrates. Results show that Ga 2 O 3 / m -sapphire exhibits the lower electrical resistivity than its counterpart grown on c -sapphire. Activation energies of acceptor levels were estimated at ~1.4 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mi>eV</mml:mi> </mml:mrow> </mml:mrow> </mml:math> and ~0.7 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mi>eV</mml:mi> </mml:mrow> </mml:mrow> </mml:math> , for Ga 2 O 3 films grown on c - and m -plane, respectively. This result shows that growing Ga 2 O 3 on m -plane sapphire is beneficial to reach a weakly compensated sample. Cathodoluminescence analysis suggests that the additional low activation energy of ~0.18 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mi>eV</mml:mi> </mml:mrow> </mml:mrow> </mml:math> observed in Ga 2 O 3 grown with the highest oxygen flow on m -plane sapphire can be associated to thermally-induced migration of self-trapped hole states.