【Domestic News】Collection of Gallium Oxide Reports by Major Academies and Universities at the "2023 Power and Optoelectronic Semiconductor Device Design and Integration Application Forum" (1)

Pei Yanli, Sun Yat-sen University: Research on Solar Blind Ultraviolet Detector Based on ε -Ga₂O₃

      During the Forum, on “optoelectronic devices and applications”, Professor Pei Yanli of Sun Yat-sen University presented a keynote report on" Research on Solar Blind Ultraviolet Detectors Based on ε-Ga₂O₃". Solar blind ultraviolet detectors are widely used in both military and civil fields, and the selection of suitable materials is one of the keys to realize the characteristics of solar blind. The forbidden band width of gallium oxide (Ga₂O₃) can be up to 5 eV, which can detect the solar blind UV band without energy band regulation. Its excellent chemical and physical properties make gallium oxide material a natural material for the development of solar blind ultraviolet detector, and there is an urgent demand in both national defense and civil fields.

      Gallium oxide has five isomers, namely α, β, γ, δ, and ε. Compared with stable β phase gallium oxide,,ε phase gallium oxide with orthogonal structure has better crystal symmetry, which can perform large area heteroepitaxy on commercial single crystal substrates such as SiC, GaN, sapphire, and therefore reduce the cost of gallium oxide-based UV detector. At the same time, ε gallium oxide is a ferroelectric semiconductor with a very strong spontaneous polarization, which will also provide a new idea for the design of a new solar-blind UV detector. At present, the high quality preparation and detector application of ε gallium oxide are not mature.

      The study is for preparing high-quality ε gallium oxide on a sapphire substrate based on the method of MOCVD. The research studies the effect on ε gallium oxide solar-blind ultraviolet detection performance by the means of preparation process, post-annealing, and treatment on surface of F ion, to reveal the mechanism affecting the detection performance such as epitaxial layer defects and surface characteristics of the device, and provide experimental and theoretical support for the development of ε gallium oxide-based solar blind ultraviolet detector.

      The research epitaxial grow Ga₂O₃ by two-step MOCVD and compared the effect of H₂O and N₂O as oxygen sources on the UV detection performance. XRD, AFM, CL and other means showed that H₂O as an oxygen source can improve the crystallization quality, reduce the defect density, and obtain the ultraviolet detection such as performance of light-dark current ratio (PDCR) of 1.0×10³, the response rise-time of 0.55s, and decay time of 0.58 s/3.14s. After post-annealing at high temperature above 700 degrees, phase transition occurs and detector performance degradation occurs. Annealing at low-temperature can effectively eliminate the point defects such as oxygen vacancy, reduce the dark current, and improve the light-dark current ratio and response time characteristics. After the solar blind UV detector annealed at 640 degrees, the dark current decreased to 0.069 pA, the rejection ratio (Rpeak / R400) reached 2.4×10⁴, and the light-dark current ratio reached 3×10⁵.  Dimensional electron gas was applied on the surface during the F treatment, improving the detector Ohmic contact characteristics. Meanwhile, electron potential wells on the surface improved the response time of the device, which significantly increased detection sensitivity and improved gain.

Zhang Maolin, Nanjing University of Posts and Telecommunications: Research on Gallium Oxide Material Growth and Array Detector

      During the Forum, on “Optoelectronic devices and their applications”, Zhang Maolin of Nanjing University of Posts and Telecommunications brought the theme report of "Gallium oxide material growth and array detector research", whose main research direction is focusing on the preparation of wide band gap semiconductor gallium oxide (Ga₂O₃) crystal and device physics research; Optimizing its crystal quality, catching up with the international level, and developing the system application of related devices are also the main research directions.

      The report shares the progress and achievements of thin film CVD growth and array detectors and applications. MOCVD growth / substrate preparation, LSPR enhanced Pt / Ga₂O₃ composite film photoresponse, PECVD growth Ga₂O₃ film, and Mist-CVD growth phase Ga₂O₃ film are detailed in the report. It also reports  Ga₂O₃-based solar blind UV detection array device (44), 16 unit Ga₂O₃ rectangular array, UV imaging of wafer Ga₂O₃ array detector, UV communication of wafer Ga₂O₃ array detector, self-powered Ga₂O₃ fundamental Schottky photodiode array and other research contents.

      The research improves PECVD based on existing equipment technology and grows Ga₂O₃ film via Mist-CVD; use LSPR to enhance the optical response of Pt / Ga₂O₃ composite film and improve the detector performance; LSPR was used to enhance the optical response of Pt / Ga₂O₃ composite film and improve the detector performance. The research expands the scale of Ga₂O₃ array detector, studying the MSM structure array and Schottky array respectively; From the perspective of ultraviolet imaging and communication aspects, the application range of Ga₂O₃ array detector is expanded.

      It is said that the scientific research team of Gallium Oxide Semiconductor Innovation Center (IC-GAO), Nanjing University of Posts And Telecommunications , realized the Ga₂O₃ epitaxial growth in 2014, developed the first GAO based solar blind ultraviolet detector prototype device, and published the first academic paper. In 2016, Ga₂O₃ has become one of the active scientific research themes of Beijing University of Posts and Telecommunications. In 2017, the team obtained 2-inch high-quality epitaxy, developed the first solar-blind ultraviolet detection array device, and became the most active research group in the field of gallium oxide, and established Beijing Gallium Technology Co., Ltd. to take the road of industrialization practice. In 2018, the research team undertook the key research and development plan of Beijing Science and Technology Commission, breaking through the 3-inch crystal and epitaxial technology. After breakthrough in 2-to 4-inch single crystal growth and epitaxy technology, small batch of 2-inch single crystal substrate and epitaxial sheet are supplied and realized the 16×16 photodetector array. In 2023, it completed A round of financing of 65 million yuan, with a valuation of 250 million yuan.

Xu Xiangyu, Xiamen University: Research on gallium oxide defect, alloying electronic structure regulation and solar-blind photodetector

      During the Forum, on “Optoelectronic devices and their applications”, Xu Xiangyu of Xiamen University brought a theme report on "Research on gallium oxide defects, regulation of alloying electronic structures and solar-blind photodetectors". The report shares the performance regulation of high performance Ga₂O₃ photodetectors, as well as the photoelectric regulation and electronic structure of Al / In alloy films.

      The study shows that through the annealing of the epitaxial film, solar blind UV detector with the high responsiveness and high detection rate can achieve the sensitive response to the actual solar blind signal. The report explains the large improvement in the device performance, which is jointly influenced by the defects caused by the annealing and the surface state changes. Through Al / In alloying of Ga₂O₃, a wide range of band gap regulation is realized, a UV photodetector responding to the full solar blind band is prepared, and the reports also explained the effect of the introduction of alloy components on the band structure.