Bandgap Tailoring of Monoclinic Single‐Phase β‐(AlxGa1−x)2O3 (0 ≤ x ≤ 0.65) Thin Film by Annealing β‐Ga2O3/Al2O3 Heterojunction at High Temperatures

Herein, bandgap tuning of monoclinic (−201)‐oriented β‐(AlxGa1−x)2O3 thin films is achieved through a β‐Ga2O3/Al2O3 heterojunction by a feasible annealing process with an O2 atmosphere. During the annealing process, Al atoms of the Al2O3 substrate outdiffuse easily into the β‐Ga2O3 thin film deposited by ozone‐assisted molecular beam epitaxy (OMBE). The Al compositions in the β‐(AlxGa1−x)2O3 samples are tuned through adjusting the annealing temperature from 800 to 1300 °C and experimentally determined from the result of X‐ray photoelectron spectroscopy (XPS) measurements combined with Vegard's law. Successive Al‐composition‐gradient β‐(AlxGa1−x)2O3 thin films with controlled bandgap are constructed. On these bases, β‐Ga2O3 thin films are deposited on β‐(AlxGa1−x)2O3 (0 ≤ x ≤ 0.65) substrates through OMBE, yielding β‐Ga2O3/β‐(AlxGa1−x)2O3 (0 ≤ x ≤ 0.65) heterojunction structures, and the band offsets of this heterojunction are determined by XPS accordingly. This methodology to achieve high‐quality β‐(AlxGa1−x)2O3 thin films with adjustable Al composition and tunable band offsets of the β‐Ga2O3/β‐(AlxGa1−x)2O3 interface will provide guidance for potential strategies to develop and fabricate β‐(AlxGa1−x)2O3‐based deep‐UV photodetectors and power devices.

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