κ/β-Ga₂O₃ Type-II Phase Heterojunction.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Semiconductor Devices

Background:

• Ultrawide-bandgap gallium oxide (Ga₂O₃) is crucial for solar-blind photonics and high-power electronics.
• Band alignments between different Ga₂O₃ polymorphs are poorly understood due to fabrication challenges.
• Heterojunctions of different phases can exhibit unique band offsets despite similar stoichiometry.

Purpose of the Study:

• To experimentally demonstrate a heterojunction between different gallium oxide phases (β-Ga₂O₃/κ-Ga₂O₃).
• To investigate the band alignment and interfacial properties of this novel phase heterojunction.
• To evaluate the performance of photodetectors based on this heterojunction for deep ultraviolet (DUV) applications.

Main Methods:

• Fabrication of a β-Ga₂O₃/κ-Ga₂O₃ stacked phase heterojunction.
• Characterization of the heterojunction interface and band alignment using electrical and optical measurements.
• Fabrication and testing of photodetectors using bare β-Ga₂O₃, κ-Ga₂O₃, and the phase heterojunction.

Main Results:

• Successful demonstration of a β-Ga₂O₃/κ-Ga₂O₃ phase heterojunction with a sharp interface.
• Discovery of an unprecedented type-II band alignment with significant band offsets (≈0.65 eV/0.71 eV).
• Phase heterojunction photodetector showed a responsivity increase of three orders of magnitude and improved response times under DUV illumination without external bias.

Conclusions:

• The β-Ga₂O₃/κ-Ga₂O₃ phase heterojunction exhibits a type-II band alignment suitable for self-powered DUV detection.
• The observed high responsivity and fast response times confirm a strong interfacial electric field, beneficial for electron-hole separation.
• This work opens new avenues for utilizing phase heterojunctions in advanced electronic and photonic devices based on ultrawide-bandgap semiconductors.