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.