The energy band alignment between atomic layer deposited (ALD) high-k dielectrics of ZrO2 and HfO2 with n-type β-Ga2O3 was evaluated using x-Ray photoelectron spectroscopy. The valence band offset was found to be −0.3 ± 0.04 eV and −0.5 ± 0.04 eV for ZrO2and HfO2, respectively, which produced type II, staggered gap alignments for both dielectrics with conduction band offsets greater than 1 eV. Capacitance-voltage measurements were conducted on metal-oxide-semiconductor (MOS) diodes and used to extract the dielectric constants (ɛ) of both oxides. ZrO2films had a nearly ideal ɛ of 24.7 (ɛ ∼ 25), while HfO2 exhibited a significantly lower ɛ of 14 (ɛ ∼ 25–30). These results, combined with the small hysteresis (≤0.09 eV) in the capacitance-voltage behavior for both films, is indicative of the high quality of these ALD oxides and their interface with the β-Ga2O3 making them potential candidates as gate dielectrics in power devices based on this relatively new ultra-wide bandgap material.

The radiation tolerance of AlGaN/GaN high electron mobility transistors (HEMTs) fabricated on high quality, low threading dislocation density (TDD) ammonothermal GaN and hydride vapor phase epitaxy GaN substrates was studied and compared to the radiation response of devices on SiC substrates where the TDD is 10 4 times higher. Hall and transport measurements were performed as a function of 2 MeV proton fluence. The threading dislocation density had no effect on the radiation response. Comparing the results with published data reveals that almost all irradiated GaN-based HEMTs respond to radiation damage similarly regardless of differences in initial film quality, device structure, aluminum mole fraction, etc. AlGaAs/GaAs HEMTs are also shown to behave similarly but are around ten times more sensitive to radiation damage than GaN-based HEMTs. Known values of the displacement energy thresholds in GaN and GaAs are used to calculate that 36% fewer defects are created in GaN than in GaAs, which is too small to cause a 1000% difference in radiation sensitivity between GaN-and GaAs-based HEMTs. An alternative explanation is proposed in which the piezoelectric field at the AlGaN/GaN interface causes scattered carriers to be reinjected into the 2DEG channel, thereby mitigating some of the harmful radiation effects.

The electrical quality of HfO2 dielectrics grown by thermal atomic layer deposition at 175 °C on n-type (2¯01) β-Ga2O3 has been studied through capacitance- and current-voltage measurements on metal-oxide-semiconductor capacitors. These capacitors exhibited excellent electrical characteristics, including dual-sweep capacitance-voltage curves with low hysteresis and stretch-out and a frequency-stable dielectric constant of k∼14 when measured between 10 kHz and 1 MHz. The C-V curves exhibited a uniform and repeatable +1.05 V shift relative to the ideal case when swept from 3.5 to −5 V, yielding positively measured flatband (+2.15 V) and threshold (+1.05 V) voltages that may be useful for normally off n-channel Ga2O3 devices. Using the Terman method, an average interface trap density of 1.3 × 1011 cm−2·eV−1 was obtained between 0.2 and 0.6 eV below the conduction band edge. The forward bias current-voltage characteristic was successfully fitted to the Fowler-Nordheim tunneling model at a field strength of 5 MV/cm, allowing an extraction of a 1.3 eV conduction band offset between HfO2 and Ga2O3, which matches the value previously determined from x-ray photoelectron spectroscopy. However, a temperature dependence in the leakage current was observed. These results suggest that HfO2 is an appealing dielectric for Ga2O3 device applications.

Temperature dependent current-voltage characteristics and Schottky barrier height are reported for 65 nm thick TiN films deposited by atomic layer deposition on (-201) β-Ga2O3 and compared with those of reference Pt Schottky contacts. Using thermionic emission theory, a thermionic emission model for both the Pt and TiN Schottky contacts to (-201) β-Ga2O3 was determined. Both contacts had comparable barrier heights of about 1 eV and near-unity ideality factor values, independent of temperature. The TiN contact had about an order of magnitude lower reverse current at room temperature, however, at high temperature the reverse current of the Pt contact was substantially lower (0.27 mA/cm2).

There has been significant research on graphene as a sensor owing to the inherent high sensitivity and surface area associated with two-dimensional (2D) materials. Often, the ability of graphene to form heterojunctions with wide-bandgap semiconductors is overlooked. In this study, we present a detector based on an epitaxial graphene/SiC heterojunction, exploiting the 2D nature of graphene to minimize absorption losses for high-efficiency sensing while simultaneously taking advantage of the epitaxial p–n junction to achieve low reverse leakage. We measured a quantum efficiency above 80% at 4 eV using a graphene/SiC p–n heterojunction with a dark current <1 nA/cm2.