The temperature-dependent behavior of on/off ratio and reverse recovery time in vertical heterojunction p-NiO/β n-Ga2O/n+ Ga2O3 rectifiers was investigated over the temperature range of 25–300 °C. The device characteristics in forward bias showed evidence of multiple current transport mechanisms and were found to be dependent on the applied bias voltages and temperatures. The on–off ratio decreased from 3 × 106 at 25 °C to 2.5 × 104 at 300 °C for switching to 100 V reverse bias. For 200 μm diameter rectifiers, the reverse recovery time of ∼21 ns was independent of temperature, with the Irr monotonically increasing from 15.1 mA at 25 °C to 25.6 mA at 250 °C and dropping at 300 °C. The dI/dt increased from 4.2 to 4.6 A/μs over this temperature range. The turn-on voltage decreased from 2.9 V at 25 °C to 1.7 V at 300 °C. The temperature coefficient of breakdown voltage was negative and does not support the presence of avalanche breakdown in NiO/β-Ga2O3 rectifiers. The energy loss during switching from 100 V was in the range 23–31 μJ over the temperature range investigated.
The characteristics of sputtered NiO for use in pn heterojunctions with Ga2O3 were investigated as a function of sputtering parameters and postdeposition annealing temperature. The oxygen/ nickel and Ni2O3/NiO ratios, as well as the bandgap and resistivity, increased as a function of O2/Ar gas flow ratio. For example, the bandgap increased from 3.7 to 3.9 eV and the resistivity increased from 0.1 to 2.9 Ω cm for the O2/Ar ratio increasing from 1/30 to 1/3. By sharp contrast, the bandgap and Ni2O3/NiO ratio decreased monotonically with postdeposition annealing temperatures up to 600 °C, but the density of films increased due to a higher fraction of NiO being present. Hydrogen is readily incorporated into NiO during exposure to plasmas, as delineated by secondary ion mass spectrometry measurements on deuterated films. The band alignments of NiO films were type II-staggered gaps with both α- and β-Ga2O3. The breakdown voltage of NiO/β-Ga2O3 heterojunction rectifiers was also a strong function of the O2/Ar flow ratio during deposition, with values of 1350 V for 1/3 and 830 V for 1/30.
more » « less- Award ID(s):
- 1856662
- NSF-PAR ID:
- 10440210
- Publisher / Repository:
- American Vacuum Society
- Date Published:
- Journal Name:
- Journal of Vacuum Science & Technology A
- Volume:
- 41
- Issue:
- 1
- ISSN:
- 0734-2101
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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The characteristics of NiO/
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Vertical geometry NiO/β n-Ga2O/n+ Ga2O3 heterojunction rectifiers with contact sizes from 50 to 200 μm diameter showed breakdown voltages (VB) up to 7.5 kV for drift region carrier concentration of 8 × 1015 cm−3. This exceeds the unipolar 1D limit for SiC and was achieved without substrate thinning or annealing of the epi layer structure. The power figure-of-merit, VB2/RON, was 6.2 GW cm−2, where RON is the on-state resistance (9.3–14.7 mΩ cm2). The average electric field strength was 7.56 MV/cm, approaching the maximum for β-Ga2O3. The on–off ratio switching from 5 to 0 V was 2 × 1013, while it was 3 × 1010–2 × 1011 switching to 100 V. The turn-on voltage was in the range 1.9–2.1 V for the different contact diameters, while the reverse current density was in the range 2 × 10−8–2 × 10−9 A cm−2 at −100 V. The reverse recovery time was 21 ns, while the forward current density was >100 A/cm2 at 5 V.more » « less
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