Ni/TiO2/ $\beta$-Ga2O3 Heterojunction Diodes with NiO Guard Ring Simultaneously Increasing Breakdown Voltage and Reducing Turn-on Voltage

Beta Gallium Oxide ( $\beta$ -Ga 2 O 3 ) is an ultra-wide bandgap semiconductor (∼4.8 eV) with numerous merits positioning it to surpass the material limits other semiconductors for power electronic applications, namely a high predicted critical field strength of 8 MV/cm, controllable doping with multiple shallow donor species, and melt-grown substrates facilitating high quality, lattice matched epitaxial growth. Vertical Schottky diodes are a fundamental application for $\beta$ -Ga 2 O 3 to demonstrate power handling capabilities; however, breakdown behavior is limited by electric field crowding at the contact edge and high tunneling current under large reverse bias. P-type nickel oxide (NiO) has been investigated for p-n heterojunction diodes (HJD) [1], and edge termination [2], but the p-n barrier significantly raises the turn-on voltage (V on ), increasing forward conduction losses. The TiO 2 /Ga 2 O 3 heterojunction has been shown to improve off-state losses and breakdown voltage (V bk ) without adding significant on-state losses [3]. Leakage current is reduced by the additional barrier width, but the negative conduction-band offset between TiO 2 and $\beta$ -Ga 2 O 3 maintains low V on . This work explores Ni/TiO 2 / $\beta$ -Ga 2 O 3 heterojunction diodes with a p-NiO guard ring (GR), which reduces V on compared to a co-fabricated SBD while exceeding the breakdown field of SiC and GaN.