(Keynote) Nitrogen-Ion Implantation Doping of Ga2O3 and Its Application to Transistors

As a key ultra-wide bandgap semiconductor, gallium oxide (Ga 2 O 3 ) 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 Ga 2 O 3 device technologies. Recently, we succeeded in developing nitrogen (N)-ion implantation doping technology to form p -type Ga 2 O 3 [1]. Note that it is almost impossible to obtain p -type Ga 2 O 3 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 Ga 2 O 3 , which is composed of O 2 p orbitals, is characterized by a very large hole effective mass and conduces to self-trapping of holes with associated characteristic lattice distortions. Therefore, p -Ga 2 O 3 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 -Ga 2 O 3 region formed in n -Ga 2 O 3 can be utilized as a current blocking layer. In this talk, we first discuss the material properties of p -Ga 2 O 3 formed by N-ion implantation doping. Then, the device process and characteristics of vertical normally-on Ga 2 O 3 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).