AZO interlayers between n-Ga2O3 and Ti/Au metallization significantly enhance Ohmic contact formation after annealing at ≥ 300°C. Without the presence of the AZO, similar anneals produce only rectifying current-voltage characteristics. Transmission Line Measurements of the Au/Ti/AZO/Ga2O3 stacks showed the specific contact resistance and transfer resistance decreased sharply from as-deposited values with annealing. The minimum contact resistance and specific contact resistance of 0.42 Ω-mm and 2.82 × 10-5 Ω-cm2 were achieved after a relatively low temperature 400°C annealing. The conduction band offset between AZO and Ga2O3 is 0.79 eV and provides a favorable pathway for improved electron transport across this interface.

The performance of arrays consisting of 21 β-Ga2O3 field-plated rectifiers fabricated on thick epitaxial layers (n-type carrier concentration ∼1.6 × 1016 cm−3) grown on conducting substrates (carrier concentration 3 × 1019 cm−3) is reported. We show that by interconnecting the output of 21 smaller (0.4 × 0.4 mm2 to 1 × 1 mm2, total area 0.09 cm2) individual rectifiers using e-beam deposited Au, we can achieve a high total forward output current of 33.2 A, at 4.25 V in the single-sweep voltage mode, and a low forward turn-on voltage of 2.9 V (defined at 100 A cm−2) and maintain a reverse breakdown voltage of 240 V (defined at 1 μA cm−2). The current density was 376 A cm−2, and the on-state resistance was 0.012 Ω cm2. The total forward current was 10 A at 1.9 V and 22 A at 3 V. The power figure-of-merit for the array, VB2/RON, was 4.8 MW cm−2, with a reverse recovery time of individual rectifiers of 32 ns. The on/off ratio of the rectifier array was in the range of 105–1010 for +1 V/−1 to −100 V.

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The use of ITO interlayers between Ga2O3 and Ti/Au metallization is shown to produce Ohmic contacts after annealing in the range of 500–600 °C. Without the ITO, similar anneals do not lead to linear current–voltage characteristics. Transmission line measurements were used to extract the specific contact resistance of the Au/Ti/ITO/Ga2O3 stacks as a function of annealing temperature. Sheet, specific contact, and transfer resistances all decreased sharply from as-deposited values with annealing. The minimum transfer resistance and specific contact resistance of 0.60 Ω mm and 6.3 × 10−5 Ω cm2 were achieved after 600 °C annealing, respectively. The conduction band offset between ITO and Ga2O3 is 0.32 eV and is consistent with the improved electron transport across the heterointerface.

Films of β-Ga2O3 grown by halide vapor phase epitaxy on native substrates were subjected to Ar inductively coupled plasma treatment. As a result, the built-in voltage of Ni Schottky diodes deposited on the plasma treated surfaces decreased from 1 V to −0.02 V due to the buildup of deep trap concentration in the near surface region. Deep level spectra measurements indicate a strong increase in the top ∼200 nm of the plasma treated layer of the concentration of E2* (Ec − 0.8 eV) and especially E3 (Ec − 1.05 eV) deep electron traps. Capacitance-voltage profiling with monochromatic illumination also indicated a large increase in the upper ∼100 nm of the film in the concentration of deep acceptors with optical threshold for an ionization of ∼2.3 eV and 3.1 eV. Such defects at the surface led to a significant increase in reverse current, an increase in the ideality factor in forward current, and a dramatic decrease in the diffusion length of nonequilibrium charge carriers from 450 nm to 150 nm.