【Domestic Papers】Ultrahigh Performance of Self-Powered Far-UVC Detector Based on MOCVD-Grown α-Ga₂O₃ Thin Film on c-Al₂O₃ Without Any Phase Stabilizer

      Researchers from the Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences have published a dissertation titled "Ultrahigh Performance of Self-Powered Far-UVC Detector Based on MOCVD-Grown α-Ga₂O₃ Thin Film on c-Al₂O₃ Without Any Phase Stabilizer" in Journal of Alloys and Compounds.

Project Support

      This work is supported by the National Natural Science Foundation of China (62574203, 12204474, 12304111, and 12304112).

Background

      As an emerging ultrawide band gap semiconductor, α-Ga₂O₃, with the widest bandgap of ~5.4-5.6 eV among gallium oxide isomers, is a naturally ideal candidate material for far-ultraviolet-C (far-UVC, 200-240 nm) photodetection, offering broad application prospects in bacteria and viruses inactivation, gas monitoring (such as NO, NO₂ and NH₃), photo-lithography, and so on. Till now, owing to the same corundum crystal structure, α-Ga₂O₃ epilayers have been commonly achieved on sapphire substrates by using various methods, including mist chemical vapor deposition (Mist-CVD), halide vapor phase epitaxy (HVPE) metal-organic chemical vapor deposition (MOCVD) and pulsed laser deposition. Among these, the MOCVD method offers unique advantages, such as precise control over the film phase composition and growth rate, high purity, high uniformity, low surface roughness, and suitability for commercial mass production. However, all the reported MOCVD epitaxial growth of α-Ga₂O₃ films to date has required the use of sapphire substrates with specific orientations (such as m- and r-Al₂O₃) or the additional introduction of other sources as phase stabilizers (such as HCl and triethylboron (TEB)) during the growth process to be achieved. This not only increases the cost and complexity of the preparation, but also often leads to problems such as poor crystalline quality, a small bandgap, and phase impurities in α-Ga₂O₃ films. Therefore, the development of far-UVC photodetectors based on MOCVD-grown pure α-Ga₂O₃ films remains an unexplored frontier.

Abstract

      α-Ga₂O₃ with an ultra-wide bandgap holds significant application potential in far-ultraviolet-C (far-UVC) photodetection. Currently, the methods for epitaxial growth of α-Ga₂O₃ thin films via metal organic chemical vapor deposition (MOCVD) all require the use of sapphire substrates with specific orientations, or the additional introduction of phase stabilizers, which increases the complexity of preparation and affects the optoelectronic properties of the films as well as the performance of devices. In this work, high-quality pure-phase α-Ga₂O₃ thin films have been achieved on c-Al₂O₃ by using MOCVD technique without any phase stabilizer for the first time. 120 nm-thick α-Ga₂O₃ thin film exhibits a narrow X-ray rocking curve full width at half maximum of 0.05°, a small root-mean-square roughness of 0.429 nm, and an ultra-wide band gap of 5.4 eV, representing the best result achieved for α-Ga₂O₃ thin films prepared by the MOCVD method to date. Leveraging this α-Ga₂O₃ film, a self-powered far-UVC Pt/α-Ga₂O₃/Al planar Schottky photodiode was successfully developed. This device showcases a significant responsivity of 8.4 mA/W at 222 nm, an ultrafast response time of 0.8 μs and a record-high far-UVC to near-UVC rejection ratio (R_{222 nm}/R_{255 nm}) of 3.42×10² at room temperature under 0 V. Furthermore, the detector possesses excellent operational stability and robust resistance to high temperature of up to 200 °C. This study demonstrates a feasible approach for preparing high-quality pure-phase α-Ga₂O₃ thin films by MOCVD, providing valuable insights for the development of high-performance self-powered far-UVC band detectors.

Highlights

      ● First MOCVD-grown pure-phase α-Ga₂O₃ on c-Al₂O₃ without phase stabilizer.

      ● The state-of-the-art crystalline quality for MOCVD-grown α-Ga₂O₃ film.

      ● High-performance self-powered α-Ga₂O₃-based far-UVC photodetector.

      ● Operational stability at 200 °C validates high-temperature application viability.

Conclusion

      In this work, a high-quality α-Ga₂O₃ film was firstly deposited onto c-plane sapphire substrate using the MOCVD technology without any phase stabilizer. Benefiting from the small lattice mismatch between α-Ga₂O₃ and c-Al₂O₃ as well as precise control of the growth conditions, we have obtained α-Ga₂O₃ epitaxial film with high crystalline quality and low surface roughness. Typically, FWHM value of the XRD rocking curve of α-Ga₂O₃ (0006) plane can reach as narrow as ~0.05°, representing the optimal value for α-Ga₂O₃ film grown by the MOCVD method. Furthermore, a self-powered far-UVC photodetector was fabricated based on this α-Ga₂O₃ film, demonstrating a high responsivity, an ultra-fast response speed and a large far-UVC to near-UVC rejection ratio at 0 V. The superior far-UVC photodetection performance of our device can be attributed to the high crystalline quality and the ultra-wide bandgap of α-Ga₂O₃ film, as well as the optimized device architecture. Meanwhile, the device also demonstrates outstanding high-temperature endurance and operational stability, highlighting the tremendous application potential of MOCVD-grown α-Ga₂O₃-based far-UVC photodetectors.