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【Member News】Shenzhen Pinghu Laboratory has Made Important Progress in Theoretical Research of Gallium Oxide
日期：2024-11-25阅读：248
Research Express
Aiming at the low energy level of Gallium Oxide valence band and the difficulty of P-type doping, the Fourth Generation Materials and Devices Research Group of Shenzhen Pinghu Laboratory has developed a new β-phase gallium-oxygen-rhodium terpolymer band-gap semiconductor based on the theory of rhodium solid solution. The results " Rhodium-Alloyed Beta Gallium Oxide Materials: New Type Ternary Ultra-Wide Bandgap Semiconductors" has been published in Advanced Electronic Materials and invited to provide journal cover design. The article has also been featured in Progress and Frontiers in Ultrawide bandgap Semiconductors. The first author is Dr. Zha Xianhu, corresponding author is Academician Zhang Daohua, and co-authors include Director Wan Yuxi and Associate Professor Li Shuang.
The power characteristics of a semiconductor material (Baliga’s Figure of Merit) are proportional to the cube of its band gap. With its ultra-wide band gap (4.9 electron volts) and proven preparation methods, Gallium Oxide is an ideal material for power devices. However, the power characteristics of the existing Gallium Oxide devices are still significantly lower than the theoretical limit of the material, because of the low valence band top energy level and energy band dispersion relationship. The impurity doped acceptor level is more than 1 electron volt, and it is difficult to achieve effective P-type conduction. Current Gallium Oxide devices are mostly based on Schottky Barriers or form p-n heterojunctions with other oxides (such as Nickel Oxide). Low Schottky Barriers and high interface states of p-n heterojunction limit the power characteristics of Gallium Oxide devices. How to realize P-type doping of Gallium Oxide has become a key problem in current research.
Figure 1. Crystal structure and band structure of β-phase Gallium Oxide.
The structure of Gallium Oxide by rhodium solid solution was investigated based on first principles. Due to the close atomic radius of rhodium to gallium, rhodium solid solution Gallium Oxide has low mixing enthalpy and high stability in solid solution configuration. This phenomenon has also been confirmed in experiments. When the Gallium Oxide crystal is grown by Pt-Rh crucible, rhodium easily enters the Gallium Oxide lattice. Based on the band structure analysis, rhodium solid solution Gallium Oxide is still a wide bandgap semiconductor, and its valence band top is formed by the hybridization of rhodium and adjacent oxygen atomic orbitals, and the corresponding energy level significantly increases compared to the valence band top of the Gallium Oxide. In addition, the band dispersion curvature near the top of the valence band increases, which is closely related to the density of electron states delocalized along the [010] crystal direction. Therefore, the authors of this work propose to grow the Gallium Oxide solid-solution Gallium Oxide epitaxy layer on the Gallium Oxide [010] crystal orientation substrate. Specifically, the semiconductor band gap of the solid solution is between 3.77 and 4.10 electron volts when the molar concentration of rhodium solid solution is in the range of 0-50%, and the valence band top energy level of the solid solution at least 1.35 electron volts increases than that of the Gallium Oxide. When the rhodium molar ratio is 25%, the hole effective mass is only 52.3% of the Gallium Oxide, which helps to realize P-type doping, expand the application range of materials and improve the performance of devices.
Figure 2, (a) and (b) show the crystal structure and band structure at 25% solid solution molar ratio of rhodium, respectively. (c) Band alignment diagram of rhodium solid solution Gallium Oxide β-(RhxGa1-x)2O3 at different molar concentrations x.
