【Domestic News】Combination of Gallium Oxide Power Devices and DUV Optoelectronic Devices (1)

01 Anisotropic optical and electric properties of β-gallium oxide

      β-Ga₂O₃ is considered as a "fourth-generation semiconductor" material after GaN and SiC because of its ultra-wide forbidden band width (Eg = 4.9 eV). β-Ga₂O₃ has been widely used in solar-blind UV detectors, including PN, PIN, Schottky and photoconductive devices. Currently reported light responsiveness is as high as 4000 A/W and response time as low as 12 ns. In addition, the breakdown field strength of β-Ga₂O₃ is up to 8 MV / cm, and the Baliga’s figure of merit reaches 3400, which proves it also an ideal material for preparing high-voltage electronic devices. The vertical Schottky diode has a high breakdown voltage of over 3000 V, and the β-Ga₂O₃ MOSFET with the field plate structure has reached an ultra-high breakdown voltage of 8.03 kV. Besides, β-Ga₂O₃ belongs to the monoclinic crystal system (space group C2/m) with low lattice symmetry. Therefore, it has rich anisotropic properties in optical, photoelectric, electrical transport, mechanical, thermal conductivity and chemical etching. Thoroughly understanding the anisotropy properties of β-Ga₂O₃ is of great importance for the preparation of reliable high-performance devices.

      Recently, Zhang Yonghui's research group of Shandong University of Technology reported the anisotropic optical and electrical properties of β-Ga₂O₃. For the anisotropy properties of β-Ga₂O₃ are rooted in its low-symmetry lattice structure, the authors first discuss in detail the different occupancy of Ga / O atoms within the β-Ga₂O₃ crystal cell. Both the Ga_IO₄ tetrahedra and Ga_IIO₆ Octahedron have two atomic chains, which is the fundamental reason that β-Ga₂O₃ can be mechanically stripped as in two-dimensional materials. Then, the paper focuses on anisotropic optical properties including optical band gap, Raman spectra and luminescent spectrum. The paper introduces the test technique of polarization Raman spectroscopy, the intensity distribution function of the Raman spectrum is calculated with the Raman tensor in three different modes. Finally, the research progress of solar-blind ultraviolet polarized light detectors is highlighted, and the working mechanism of three polarized light detectors is indicated and analyzed theoretically.

      β-Ga₂O₃ has rich anisotropy properties. A thorough understanding and full utilization of the anisotropic properties of β-Ga₂O₃ is important for the deep development of device applications for β-Ga₂O₃.

      The paper is published in Journal of Semiconductors, titled “Anisotropic optical and electric properties of β-gallium oxide”.

Figure 1. The anisotropic crystal structure of β–Ga₂O₃. (a) unit crystal cell of β–Ga₂O₃. (b) 2 × 2 cells with Ga_IO₄ tetrahedral and Ga_IIO₆ octahedral chains. (c) process for mechanical stripping of β–Ga₂O₃ nanoribbons. (d) AFM results of the typical β–Ga₂O₃ nanoribbons. (e) the lattice structure of β–Ga₂O₃; (f) The stereoscopic projection of β–Ga₂O₃ along the direction of [44,0, -5], (g) projection plane, (h) electron diffraction pattern, (i) projection diagram. (j) stereo projection of β–Ga₂O₃ along the [100] plate, (k) projection plane, (l) electron diffraction pattern, (m) projection map.

doi: 10.1088/1674-4926/44/7/071801

02 Tunneling via surface dislocation in W/β-Ga₂O₃ Schottky barrier diodes

      This paper analyzes W/β-Ga₂O₃ Schottky diodes prepared by local magnetic field sputtering at different temperatures. First, it was found that the height of Schottky barrier gradually increased with temperature raising from 100 K to 300 K, reaching 1.03 eV at room temperature.While the ideal factor decreases with increasing temperature, but is still higher than 2 at 100 K. Obviously high values of the ideal factor are associated with the tunnel effect. Second, the series and conduction resistance decrease with temperature increasing. Finally, the property of the interface dislocation is revealed by the tunneling current. The higher dislocation density suggests that dislocation-induced tunnel effect plays a dominant role in the transport mechanism. All of these findings will help to design better devices

      This paper is published in Journal of Semiconductors, titled “Tunneling via surface dislocation in W/β-Ga₂O₃ Schottky barrier diodes”.

Figure 1. The SEM cross-section diagram of the W/β-Ga₂O₃

doi: 10.1088/1674-4926/44/7/072801

03 2.83-kV double-layered NiO/β-Ga₂O₃ vertical p-n heterojunction diode with a power figure-of-merit of 5.98 GW/cm²

      Due to the lack of p-type doping technology, the design of Ga₂O₃ power device terminal is very difficult. In this paper, a high-performance NiO /β-Ga₂O₃ vertical heterojunction diode (HJDs) was prepared by using the double-layer junction terminal extension structure (DL-JTE), which consists of two layers of p-type NiO of different lengths. The bottom-60 nmp-type NiO layer completely covers the β-Ga₂O₃ surface, and the upper 60 nmp type NiO layer is 10 μm larger than the square anode electrode. Compared with the single-layer JTE, the double-layer JTE structure effectively suppressed the electric field concentration, increasing the breakdown voltage from 2020 to 2830 V. Moreover, the double-layer p-type NiO allows more holes to be injected into the Ga₂O₃ drift layer, thereby reducing the drift resistance, which decreases from 1.93 to 1.34 mΩ cm². The power figure of merit (PFOM) of devices with the DL-JTE structure is 5.98 GW/cm², which is 2.8 times that than the conventional monolayer JTE structure. These results suggest that the double-layer junction terminal extended structure provides a feasible way to prepare high-performance Ga₂O₃ heterojunction diodes.

      This paper is publish in Journal of Semiconductors , titled“2.83-kV double-layered NiO/β-Ga₂O₃ vertical p-n heterojunction diode with a power figure-of-merit of 5.98 GW/cm²”.

Figure 1. Schematic cross section of the DL-JTE / JTE device.

Figure 2. Simulated electric field distribution of HJD: (a) JTE, (b) DL-JTE bias at-2020 V, (c) the bias of the DL-JTE at-2830 V, and (d-f) the corresponding distribution of the electric field by position.

doi: 10.1088/1674-4926/44/7/072802