【Domestic Papers】Fuzhou University --- Insight into the High Hole Concentration of p-Type Ga₂O₃ via In Situ Nitrogen Doping

      Researchers from the Fuzhou University have published a dissertation titled "Insight into the High Hole Concentration of p-Type Ga₂O₃ via In Situ Nitrogen Doping" in The Journal of Physical Chemistry Letters.

Project Support

      This work was financially supported by the National Natural Science Foundation of China (Grant No. 62204270), the Major Science and Technology Special Project of Fujian Province (Grant No. 2022HZ027006), the Fujian Provincial Natural Science Foundation General Program (Grant No. 2024J01251), the Fujian Provincial Science and Technology Program Project (Grant No. 2022I0006), and the Major Science and Technology Special Project of Quanzhou Municipality (Grant No. 2022GZ7). The authors also thank Fujia Co. Ltd. for help in the growth of epitaxial films.

Background

      Gallium oxide (Ga₂O₃) holds significant potential for applications in the field of high-voltage, low-loss power electronics due to its ultra-wide bandgap of 4.95 eV and high Baliga figure of merit exceeding 3000. However, the lack of an effective p-type doping method, crucial for forming hole conduction paths to achieve avalanche characteristics in high-voltage devices, is widely recognized as a critical bottleneck for the further application of Ga₂O₃. Although p-type nickel oxide (NiO) has partially alleviated the issue of missing hole conductivity, a p-type conduction mechanism induced by nickel vacancies at room temperature (RT) is susceptible to significant reductions in hole concentration and severe device degradation under frequent switching or higher voltage/ temperature conditions.

Abstract

      The unclear p-type conduction mechanism and lack of reliable p-type Ga₂O₃ severely hinder Ga₂O₃-based high-voltage electronics. Here, we demonstrate in situ nitrogen (N) doping via metal–organic chemical vapor deposition homoepitaxy using N₂O as oxygen source and acceptor dopant. Structural and compositional analyses confirm efficient N incorporation (favored by N–Ga bonding) compensating residual Si/H donors without compromising crystallinity. The Ga₂O₃:N epilayers achieve excellent p-type performance: 1.04 × 10¹⁸ cm^–3 hole concentration, 0.47 cm² V^–1 s^–1 mobility at room temperature, and 0.168 eV activation energy. A completely new insight into the p-type conduction mechanism in Ga₂O₃ is introduced, focusing on the crystallographic visualization of acceptors (N^2–) and holes (O^–), as well as the hole excitation process. It is suggested that careful suppression of the donor compensation effect and precise control of the N chemical potential, which leads to the fabrication of trace O^– species solid-dissolved within Ga₂O₃, are essential for achieving high-hole-concentration p-type conduction in oxides.

Summary

      In summary, we propose a strategy for in situ N doping through MOCVD homoepitaxy to achieve p-type Ga₂O₃. By leveraging the high bond energy of the N−Ga bond, which is comparable to that of the O−Ga bond, and maintaining 2D step-flow growth, we successfully tuned the electrical properties of Ga₂O₃:N from n-type to p-type by modulating the growth temperature. For the first time, we achieved a high RT hole concentration of 1.04×10¹⁸ cm⁻³ and a hole mobility of 0.47 cm² V⁻¹ s⁻¹ , accompanied by a low acceptor activation energy of 0.168 eV. Our results demonstrate that N acceptor impurities can be incorporated into the Ga₂O₃ lattice at high concentrations and substitute O sites at high temperature. Furthermore, a completely new crystallographic insight into the p-type conduction mechanism in Ga₂O₃:N is presented, revealing the nature of acceptors (N²⁻) and holes (O⁻) in ptype conductivity oxides, along with the chemical reaction process N²⁻ + O²⁻ → N³⁻ + O⁻) underlying the activation of shallow-level acceptors. It is suggested that, for successful semiconductor-grade p-type Ga₂O₃ fabrication, the donor compensation effect induced by defects or unintentional doping impurities must be strictly controlled to sufficiently low levels, enabling acceptor-type N_O defects to dominate, and thereby allowing a small amount of O⁻ species to be stably solid-solved within the Ga₂O₃ lattice. This work presents a potential pathway for the application of p-type Ga₂O₃ in high-voltage power devices.

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