As a key ultra-wide bandgap semiconductor, gallium oxide (Ga₂O₃) has been attracting much interest for power device applications due to its excellent material properties based on an extremely large bandgap of 4.5 eV and the availability of high-quality, large-diameter wafers produced from bulk single crystals synthesized by melt growth methods. Despite having received only little attention, the ease of both n- and p-type ion implantation doping is another very attractive and important feature for Ga₂O₃ device technologies.

Recently, we succeeded in developing nitrogen (N)-ion implantation doping technology to form p-type Ga₂O₃ [1]. Note that it is almost impossible to obtain p-type Ga₂O₃ with effective hole conductivity as for conventional semiconductors. This is not only due to a lack of shallow acceptors with moderate activation energies but also because the valence band structure of Ga₂O₃, which is composed of O 2p orbitals, is characterized by a very large hole effective mass and conduces to self-trapping of holes with associated characteristic lattice distortions. Therefore, p-Ga₂O₃ is only useful for engineering large energy barriers in the form of p-n junctions. We have experimentally confirmed that a N-ion implanted p-Ga₂O₃ region formed in n-Ga₂O₃ can be utilized as a current blocking layer.

In this talk, we first discuss the material properties of p-Ga₂O₃ formed by N-ion implantation doping. Then, the device process and characteristics of vertical normally-on Ga₂O₃ MOSFETs fabricated by using multiple Si- and N-ion implantations are presented [2].

This work was partially supported by Council for Science, Technology and Innovation (CSTI), Cross-ministerial Strategic Innovation Promotion Program (SIP), “Next-generation power electronics” (funding agency: New Energy and Industrial Technology Development Organization).

[1] M. H. Wong, C.-H. Lin, A. Kuramata, S. Yamakoshi, H. Murakami, Y. Kumagai, and M. Higashiwaki, Appl. Phys. Lett. 113, 102103 (2018).

[2] M. H. Wong, K. Goto, H. Murakami, Y. Kumagai, and M. Higashiwaki, IEEE Electron Device Lett. 40, 431 (2019).