Modern power electronics seeks materials that can operate at high voltages without significant losses. β-Ga2O3 attracts attention due to its wide bandgap and critical field up to 8 MV/cm, which theoretically enables compact and efficient power converters. However, in practice, MOCVD-grown layers on the (010) orientation suffer from damage during NiOx sputtering, which is needed to create a heterojunction. This damage reduces carrier concentration and increases resistance, preventing the material's potential from being realized. This work sits alongside research on thermal conductivity and superconductivity, but it solves a specific technological problem for gallium oxide.
First, an epitaxial layer with a thickness of 6.2 μm and a donor concentration of 2.67×10¹⁶ cm⁻³ was grown on a conductive Sn:β-Ga2O3 (010) substrate by MOCVD at 1000 °C. Then, a thin NiOx layer of 7 nm was deposited on the front side by electron-beam evaporation, which does not create ion damage. On top of this layer, a thicker NiOx (9 nm p-type and 20 nm p+-type) was sputtered to form the heterojunction. To increase the breakdown voltage, a field plate made of 1 μm SiO2 was added. The fabricated diodes were measured using Keysight B1505A and Keithley 4200 analyzers, and to prevent arcing, the sample was immersed in the dielectric fluid Fluorinert FC-40.
The fabricated diodes showed a current of 700 A/cm² at a forward voltage of 4 V and a specific resistance of 2.36 mΩ·cm². The ideality factor was 1.29, the built-in potential was 2 V, and the forward-to-reverse current ratio reached 10¹¹. The breakdown voltage with the field plate was 1.64 kV, corresponding to a parallel electric field of 4.02 MV/cm. This is a record for vertical diodes on (010) layers grown by MOCVD. The calculated power figure of merit (PFOM) is 1.14 GW/cm². Comparison with Schottky diodes on the same material showed that the specific resistance increased by only 1.4 times, whereas without the protective NiOx layer it increased by 9.4 times.
This work demonstrates that a thin electron-beam-deposited NiOx layer effectively protects the (010) β-Ga2O3 surface from ion damage during subsequent sputtering. This paves the way for high-voltage heterojunction diodes on MOCVD-grown layers, which previously lagged behind HVPE layers in breakdown field. Unlike related studies that used other protection methods or different orientations, this work shows for the first time that low resistance and high breakdown field can be combined on (010) MOCVD layers. The result confirms that MOCVD technology can compete with HVPE for power devices.
The next step could be optimizing the field plate dielectric, as its contribution to increasing the breakdown voltage was modest (120 V). The long-term stability of such diodes and their behavior at high temperatures also warrant investigation. It may be possible to further reduce the specific resistance by improving the NiOx/Ga2O3 interface. In the future, such diodes could become the foundation for compact converters in data centers and electric vehicles.
The results will influence the development of β-Ga2O3-based power semiconductor devices, especially for applications above 1 kV. They may also accelerate the adoption of MOCVD technology in the production of gallium oxide devices.
Plans include improving the field plate and testing the diodes under prolonged load. The applicability of the method to other orientations, such as (011) and (001), should also be explored.
For β-Ga2O3 power electronics, the issue of stability and reliability under high fields and temperatures remains unresolved. Also open is the question of maximum doping concentrations and mobility in MOCVD layers, which limit the on-resistance.
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What the work does
The work presents a vertical diode based on β-Ga2O3 grown by MOCVD on the (010) orientation. To protect the surface from damage during ion sputtering of NiOx, a thin NiOx layer was deposited by electron-beam evaporation before the thick layer was applied. This made it possible to achieve a breakdown field of 4.02 MV/cm at a voltage of 1.64 kV, a specific resistance of 2.36 mΩ·cm², and a figure of merit of 1.14 GW/cm², which is a record for MOCVD layers on (010).
Where its strength is
The key strength of the work lies in the technological solution that makes it possible to combine low on-state resistance with a high breakdown field in MOCVD layers on (010), which had previously lagged behind HVPE. The protective NiOx layer, deposited without ion damage, opens the way to the practical use of MOCVD for Ga2O3 power electronics.
Where it could go next
Worth trying
Why this may matter
This result could accelerate the adoption of β-Ga2O3 in power electronics, because MOCVD is a more scalable method than HVPE. Achieving high breakdown fields in MOCVD layers opens the way to the production of efficient and compact power converters.
Nearby works in our archive
The archive is sparse around this work: the closest review is only 0.52, against a usual 0.64. It looks like few have drilled nearby.
The critical field of β-Ga2O3 is roughly twice that of silicon carbide, allowing devices to be four times thinner at the same voltage. And the 7 nm NiOx layer used here is thousands of times thinner than a human hair.