Beta-gallium oxide (β-Ga2O3) holds enormous potential for medium voltage range power electronic applications. This work reports VBr > 10 kV/Ron,sp = 43 mΩ*cm2 class edge terminated vertical heterojunction diodes (HJDs) with e-beam/sputtered nickel oxide (NiOx) stack on epitaxial (011) β-Ga2O3. The power figure of merit (PFOM) of the HJD exceeds 2.3 GW/cm2. The extracted parallel plane breakdown field is > 5.3 MV/cm, which is the highest reported electric field for thick (011) β-Ga2O3 epitaxial drift layer.

In this work, sub-bandgap photoluminescence imaging is presented as a means with which to identify defect bands in bulk AlN. Sub-bandgap photoluminescence spectroscopy revealed large variations across different points in the mid-gap between 1.8 and 3.8 eV, which was subsequently investigated using broad-area photoluminescence imaging. Two different LEDs (340 and 450 nm) were used to spatially identify defect bands present in the UV and visible ranges. Bandpass filters were used at wavelengths between 450 and 700 nm to further deconvolve bands of interest at different wafer points. Raman spectroscopy was performed at each wafer point to ensure that changes in the photoluminescence were not due to the presence of different phases or low crystal quality. Measurements on both wafers revealed E 2 (high) peaks with full-width half maximum (FWHM) values below 10 cm −1 at all measured points, suggesting a high degree of crystallinity at all points, as would be expected with high quality bulk substrates. HRXRD measurements subsequently confirmed that the substrates were of high quality and phase uniform across the entire wafer surface.

We report on a phase-based lock-in thermography approach, combined with a multilayered thermal model (often employed in thermoreflectance analysis), to measure the thermal conductivity of bulk materials and layered structures. The spatial distribution of the material's thermal phase is monitored with an infrared camera, which is locked into the frequency of a modulated laser used to heat the material. This phase distribution is then fit with a thermal model, in which properties such as thermal conductivity are extracted as fit parameters. This approach enables non-contact, front-side measurements, which are insensitive to surface roughness. The technique does not strictly require the application of a transducer layer, but we highlight the practical benefits of applying a removable adhesive layer to serve as a near-surface absorber. We demonstrate the efficacy of the method by measuring materials with thermal conductivities that span over three orders of magnitude (approximately 1 W/m/K to > 2000 W/m/K).

We report 850 degrees C operation of ultrawide bandgap (UWBG) Al-rich Al0.68Ga0.32N channel high electron mobility transistors (HEMTs) at atmospheric pressure in nitrogen ambient. Temperature dependent DC electrical characteristics were measured in situ up to 850 degrees C, after exposure to 850 degrees C for 60 minutes, and at 25 degrees C after high temperature testing. At 850 degrees C (time, t = 0 min), all HEMTs tested maintained an on/off ratio greater than 10(4)(maximum of 4.6 x 10(4)). The threshold voltage demonstrated excellent stability with less than +/- 10% deviation. After returning to 25 degrees C, the devices showed negligible degradation. In fact, the off-state gate current decreased and on/off ratio slightly increased. The robustness of these UWBG AlGaN transistors at temperatures up to 850 degrees C demonstrates their viability for extreme environment applications.

In this work, we demonstrate device fabrication and characterization of ultrawide bandgap (UWBG) β-(AlxGa1−x)2O3 channel metal–semiconductor field-effect transistors (MESFETs) with Si-implanted source/drain contacts. Films of Si-doped β-(AlxGa1−x)2O3 and unintentionally doped (UID) β-Ga2O3 were grown on an Fe-doped (010) β-Ga2O3 substrate using close-injection showerhead metal–organic chemical vapor deposition (CIS-MOCVD). The Al concentration (x) of the β-(AlxGa1−x)2O3 film was estimated to be ≈21% using x-ray diffraction (XRD), and the Si doping concentration of the n-type β-(Al0.21Ga0.79)2O3 film was measured to be 2 × 1018 cm−3 using secondary ion mass spectroscopy (SIMS). Both gate-recessed and non-recessed MESFET structures were fabricated and had on/off ratios of ≈105. The gate-recessed MESFETs had a lower saturation drain current (15 mA/mm) than the non-recessed structures (26 mA/mm), but they also had a slightly lower off-state leakage current. The gate-recessed structures also enabled better modulation of the channel conductivity, which led to a positive threshold voltage shift of +8V compared with the non-recessed structures. The maximum breakdown voltages of 730 and 858 V were measured for the gate-recessed and non-recessed MESFETs, respectively. Because the thermal conductivity of the disordered alloy β-(Al0.21Ga0.79)2O3 channel is expected to be much lower than β-Ga2O3, thermoreflectance imaging was used to assess the device-level thermal performance. At a DC power density of 0.58 W/mm (VGS = 0 V), an area-averaged gate temperature rise of 54 K was measured. This work demonstrates the potential of leveraging the large-area, low-cost, high-quality β-Ga2O3 substrate platform to develop next-generation power electronics using UWBG β-(AlxGa1−x)2O3 as the active semiconductor.

The cracking and local strain relaxation in (010) (AlxGa1−x)2O3 films grown on Ga2O3 substrates are assessed in terms of film composition and thickness. We utilize x-ray diffraction and electron microscopy techniques combined with simulation and modeling to investigate that film cracking on curvature (flatness) has a directly proportional relationship with film thickness and/or aluminum content. Cross section transmission electron microscopy reveals that cracks along both the (001) and (100) cleavage planes penetrate into the substrate. The diffuse scattered intensity observed in reciprocal space maps (RSMs) is directly correlated with the tilt that is introduced due to the change in the deformation conditions near the cracks. While asymmetric RSMs show that the layers are fully strained, the diffuse scattering distribution in reciprocal space can be interpreted to show that the cracking relaxes and locally tilts the lattice ∼350 nm from the crack edges, which is consistent with the larger radius of curvature associated with the films with higher crack densities. For example, a 200 nm (Al0.13Ga0.87)2O3 thick film has an average inter-crack spacing of 3.3 µm, so most of the epitaxial layer is fully strained except near the cracks where it deforms elastically and is consistent with the gallium oxide Poisson ratio. A reciprocal space model was developed, which imports the strain and tilt distributions (based on finite element modeling) to match the features observed in the experimental maps. We also note that previous studies involving (AlxGa1−x)2O3 films may show evidence of cracking as observed in their symmetric and asymmetric RSMs.

This work demonstrates a method for 2D thermal mapping of the surface temperature rise of semiconductor devices using thermoreflectance imaging of mechanically exfoliated MoS2 flakes. Thickness-dependent thermoreflectance spectra were acquired, and the A, B, and C excitons of MoS2 were shown to have high thermoreflectance responses. The A exciton, corresponding to a probing wavelength of 675 nm, had the highest thermoreflectance response, but temperature rise (Delta T) measurements using this wavelength can be prone to nonlinear effects; nevertheless, these effects can be accounted for through calibration. Additionally, the high thermoreflectance response enables high measurement sensitivity for devices with low Delta T (e.g., <10 K), such as diamond-based electronics. The C exciton (probing wavelength of 470 nm) yielded a linear response over a larger Delta T range due to the broader energy band and inherently smaller wavelength shift per unit energy in this spectral region. Based on the findings in this work, the desired MoS2 flake thickness to optimize sensitivity for thermal measurements is <30 nm. The method was validated by comparing the surface temperature rise measured from a MoS2 flake, using 470 and 675 nm probing wavelengths, and directly from the semiconductor channel of a GaN high electron mobility transistor, using a 365 nm probing wavelength. To demonstrate the viability for thermometry of ultrawide band gap (UWBG) semiconductor devices, the method was applied to perform 2D mapping of the temperature rise of the semiconductor channel of a UWBG beta-Ga2O3 heterostructure field effect transistor. Ultimately, this work provides a framework for employing the layered morphology and highly nonlinear exciton resonance of transition metal dichalcogenides to probe the local thermal environment and also provides an avenue for probing thickness-dependent and temperature-dependent excitonic characteristics of thin layered materials.

p-type Cr2MnO4 with bandgap 3.01 eV was sputter deposited onto (201) and (001) n-type or semi-insulating beta-Ga2O3.The heterojunction of p-type CrMnO4 on n-type Ga2O3 is found to be type II, staggered gap, i.e., the band offsets are such that both the conduction and valence band edges of Ga2O3 are lower in energy than those of the Cr2MnO4. This creates a staggered band alignment, which can facilitate the separation of photogenerated electron-hole pairs. The valence band edge of Cr2MnO4 is higher than that of Ga2O3 by 1.82-1.93 eV depending on substrate orientation and doping, which means that holes in Cr2MnO4 would have a lower energy barrier to overcome to move into Ga2O3. Conversely, the conduction band edge of Cr2MnO4 is higher than that of Ga2O3 by 0.13-0.30 eV depending on substrate doping and orientation, which would create a barrier for electrons in Ga2O3 to move into Cr2MnO4. This heterojunction looks highly promising for p-n junction formation for advanced Ga2O3-based power rectifiers.

With the largest tunable bandgap in the III-N class of semiconductors (6.02eV) and high thermal conductivity, aluminum nitride (AlN) has immense potential for use in high power electronics, heat sinks, and UV detectors. N-type doping of molecular beam epitaxy (MBE) and metal organic chemical vapor deposition (MOCVD) heteroepitaxially grown AlN is typically achieved with Si, a donor in AlN, with a typical ionization energy of approximately 300 meV 1 . AlN wafers and homoepitaxially grown films consisting of AlN on SiC from different vendors of N- and Al- polarities were measured using Raman spectroscopy and photoluminescence (PL) to better understand the underlying stress and defect bands present. An increasing E 2 (high) shift in the Raman data was observed for each of the N-polar samples, though not in the Al-polar samples. This shift was found to be less than one wavenumber across a 2” wafer length from the center to the edge, but was consistent, suggesting existing tensile stress on the central region of the wafer, with decreasing tensile stress towards the edge. PL defect bands of interest include (i) one centered near 2.40eV (516 nm), corresponding to the presence of nitrogen vacancies (V N ), (ii) one in the UV region centered around 3.6eV (344 nm) corresponding to oxygen substitution (O N ) 2 ,(iii) one near 3.0eV (413 nm) representing a secondary defect complex of V Al -O N or V Al -Si Al , potentially significant in helping to measure doping efficiency 2 , and finally, (iv) a band centered near 2.8eV (443 nm) points to a radiative recombination of highly charged aluminum vacancies (V Al ) 3-/2- and the valence band, giving rise to a visible orange luminescence 3 . X-ray diffraction (XRD) was used to look at the crystal quality of the samples tested, atomic force microscopy (AFM) was used to measure surface morphology and Young’s modulus, and optical profilometry was used to investigate the surface topography of the samples on a larger length scale than AFM. To study n-type doping efficiency in AlN, 400nm Si-doped films were grown. Due to the presence of large defect bands in the bulk material and the deep donor level of the Si, many dopants are not ionized and instead become deep acceptors. This leads to a significant reduction in the number of freely ionized carriers in the material, diminishing the potential electrical properties of the material. To solve this issue, the temperature of the sample is increased, which increases the number of ionized carriers, and moves the operational mode closer to the intrinsic region. Temperature dependent Hall effect studies of Al- and N-polar substrates were investigated in this work with regards to carrier concentration and doping efficiency, whose results can then be extrapolated to lower temperatures. Capacitance-voltage (C-V) testing was performed to further characterize the interface trap states, carrier lifetimes, and doping, while the transmission line model (TLM) was used to measure the impact of defects on metal-semiconductor contact resistivity. In this work, doping efficiency, defect structures, and electrical transport properties in AlN were characterized, with an eye on enhancing its electrical performance and practical applications. References: [1] R. Zeisel et al., Physical Review B, vol. 61, no. 24, Jue 2000. doi: 10.1103/physrevb.61.r16283 [2] J. S. Harris et al. , “On compensation in Si-doped AlN,” Applied Physics Letters , vol. 112, no. 15, Apr. 2018. doi:10.1063/1.5022794 [3] A. Sedhain, J.Y. Lin, and H.X. Jiang, “Nature of optical transitions involving cation vacancies and complexes in AlN and AlGaN,” Applied Physics Letters , vol. 100, no. 22, May 2012. doi: 10.1063/1.4723693

We report back-end-of-line growth of nanocrystalline diamond (NCD) on ultrawide bandgap (UWBG) high Al content aluminum gallium nitride (AlGaN) channel high electron mobility transistors for thermal management. A thin (∼15 nm) silicon nitride (SiNx) interlayer was deposited to protect the device surface before performing a low temperature (500 °C) NCD growth process in an attempt to protect the gates on these fully fabricated devices. Notably, atomic force microscopy showed that the maximum lateral grain size exceeded 300 nm even though the film thickness was ∼250 nm. Comparing electrical (DC) performance before and after NCD growth, the gate leakage increased by ∼102 after NCD growth. Despite the lower NCD growth temperature, intermixing of the Ni and Au was observed in the Schottky gate metal stack; however, we believe there is another mechanism, possibly hydrogen-related, that is responsible for the measured increase in gate leakage. Regarding thermal management, the device-level thermal resistance (quantified using the average gate temperature rise measured by thermoreflectance imaging) was reduced by 29% through the incorporation of the top-side diamond film. Using time-domain thermoreflectance, the thermal conductivity of the ≈250 nm thick NCD film was measured to be 45 ± 25 W m−1 K−1. This is expected to be at least 5× greater than the thermal conductivity of the thin disordered AlGaN alloy. There could also be a coupled electrothermal component contributing to the reduced temperature rise from electric field spreading and consequent heat spreading. This study demonstrates a promising first step toward device-level thermal management of high power UWBG Al-rich AlGaN devices.

A gallium oxide (Ga2O3)–nickel oxide (NiO) merged PiN Schottky (MPS) diode was fabricated using Ga flux plasma-free etch and platinum oxide (PtOx) contacts. The use of a plasma-etch-free process enables the fabrication of Ga2O3 trenches with low surface damage. PtOx acts as both a Schottky contact to n-type Ga2O3 and an Ohmic contact to p-type NiO. Compared to the Ni/NiO contact used in many prior devices, the PtOx/NiO contact exhibits a 100 times lower contact resistance as shown by linear transfer length method measurements. This improved contact resistance boosts the diode’s forward current capacity, as featured by a second turn-on in the current–voltage characteristics with a decreased differential on-resistance. This verifies the concurrent current conduction through both Schottky and PN junctions and thereby the formation of a MPS diode. Furthermore, MPS diodes were subjected to high reverse bias reliability testing. Such a reliability test has been seldom reported in Ga2O3 devices. During an 800 V stress test (80% of the breakdown voltage) for a cumulative time of 2000 s, MPS diodes were periodically switched on, showing no degradation in the dynamic on-state characteristics. This signifies a stable PtOx–Ga2O3 Schottky contact and an improved Ga2O3–NiO heterojunction with minimal sidewall trapping as a result of the plasma-etch-free process.

p-type Cr 2 MnO 4 with bandgap 3.01 eV was sputter deposited onto (01) and (001) n-type or semi-insulating β-Ga 2 O 3 .The heterojunction of p-type CrMnO 4 on n-type Ga 2 O 3 is found to be type II, staggered gap, ie. the band offsets are such that both the conduction and valence band edges of Ga 2 O 3 are lower in energy than those of the Cr 2 MnO 4 . This creates a staggered band alignment, which can facilitate the separation of photogenerated electron-hole pairs. The valence band edge of Cr 2 MnO 4 is higher than that of Ga 2 O 3 by1.82-1.93 eV depending on substrate orientation and doping, which means that holes in Cr 2 MnO 4 would have a lower energy barrier to overcome to move into Ga 2 O 3 . Conversely, the conduction band edge of Cr 2 MnO 4 is higher than that of Ga 2 O 3 by 0.13-0.30 eV depending on substrate doping and orientation, which would create a barrier for electrons in Ga 2 O 3 to move into Cr 2 MnO 4 . This heterojunction looks highly promising for p-n junction formation for advanced Ga 2 O 3 -based power rectifiers.

p-type Cr2MnO4 with bandgap 3.01 eV was sputter deposited onto (2¯01) and (001) n-type or semi-insulating β-Ga2O3.The heterojunction of p-type CrMnO4 on n-type Ga2O3 is found to be type II, staggered gap, i.e., the band offsets are such that both the conduction and valence band edges of Ga2O3 are lower in energy than those of the Cr2MnO4. This creates a staggered band alignment, which can facilitate the separation of photogenerated electron-hole pairs. The valence band edge of Cr2MnO4 is higher than that of Ga2O3 by 1.82–1.93 eV depending on substrate orientation and doping, which means that holes in Cr2MnO4 would have a lower energy barrier to overcome to move into Ga2O3. Conversely, the conduction band edge of Cr2MnO4 is higher than that of Ga2O3 by 0.13–0.30 eV depending on substrate doping and orientation, which would create a barrier for electrons in Ga2O3 to move into Cr2MnO4. This heterojunction looks highly promising for p-n junction formation for advanced Ga2O3-based power rectifiers.

A systematic investigation was performed on the impact of the beta-gallium oxide (Ga2O3) epitaxial buffer layer thickness grown by close-injection showerhead metalorganic chemical vapor deposition (CIS-MOCVD) on the film's structural, electrical, and thermal characteristics. Varying thicknesses of unintentionally doped beta-Ga2O3 epitaxial layers were grown by CIS-MOCVD on Fe-doped (010) beta-Ga2O3 substrates, followed by a 10 nm beta-Ga2O3 Si-doped layer with a Si concentration of 10(19) cm(-3). Gate-recessed lateral metal-oxide-semiconductor field-effect transistors were fabricated with these epilayer films. The device characteristics and secondary ion mass spectroscopy results highlighted the need for precise Si doping within the channel, as well as minimizing the Si accumulation at the epilayer-substrate interface for proper device operation. The results from positron annihilation spectroscopy did not indicate a strong correlation between the epilayer thickness and Ga-related vacancies, and the thermal conductivities of the epilayers were consistent with increasing thickness as shown in the device-level frequency-domain thermoreflectance analysis.

We report the dry etching characteristics of Cr2MnO4 thin films using Cl2-based inductively coupled plasmas (ICP) for applications in Ga2O3-based power electronics, where p-n heterojunctions offer advantages over Schottky diodes. Cr2MnO4, a thermally stable p-type oxide, was deposited via RF sputter beam epitaxy and etched using Cl2/Ar and BCl3/Ar plasmas, with the latter producing much lower etch rates. The etch rates and surface roughness were investigated as functions of Cl2 flow rate, RF power, and gas composition. Results reveal that increasing the Cl2 flow rate enhances etch rates but degrades surface roughness due to non-volatile chloride formation and redeposition. Higher RF power improves surface smoothness by increasing ion bombardment energy, promoting physical sputtering, and enabling uniform etching. The etch process is ion-flux limited, with threshold energies comparable to NiO. Post-etch X-ray photoelectron spectroscopy analysis confirms that NH4OH rinsing effectively removes chlorine residues by dissolving metal chlorides and neutralizing acidic species, ensuring a clean surface. These findings underscore the importance of optimizing plasma parameters and post-etch cleaning for fabricating high-quality Cr2MnO4/Ga2O3 heterojunctions, which hold promise for high-temperature, high-power electronic applications.

We report the heteroepitaxial growth of spinel Cr2MnO4 thin films on ( 2 01 ) beta-Ga2O3 substrates via off-axis RF magnetron sputtering. Structural analysis confirms (111)-oriented epitaxial films with optimized growth at 950 degrees C. Fabricated Cr2MnO4/beta-Ga2O3 vertical diodes exhibit rectifying behavior with high on/off ratios (similar to 10(8)), turn-on voltages near 0.85 V, and low reverse leakage current. Transmission electron microscopy and atomic force microscopy analyses show the films exhibit a Stranski-Krastanov growth mode, with three-dimensional texturing of potential interest for device performance. Capacitance-voltage measurements reveal intrinsic p-type conductivity with carrier concentration similar to 7 x 10(17) cm(-3). The results suggest that Cr2MnO4 may be a promising candidate for Ga2O3-based bipolar devices.

Homoepitaxial Si-doped (010) beta-Ga2O3 epitaxial layers with thicknesses ranging from 1.2 to 12 mu m were grown simultaneously via close-injection showerhead metal-organic chemical vapor deposition on both Czochralski and edge-defined, film-fed grown (010) beta-Ga2O3:Fe substrates. Structural characterization was performed via x-ray diffraction [full-width at half maxima of 21-72 arcsec depending on epilayer thickness and substrate, measured from the symmetric (020) reflection], x-ray topography, Raman spectroscopy, cathodoluminescence spectroscopy, and transmission electron microscopy. Surface characterization was performed via atomic force microscope (AFM) and Nomarski imaging, and electrical characterization was performed via electron paramagnetic resonance spectroscopy and Hall effect measurements. In addition, thermal conductivity was measured via steady-state thermoreflectance. AFM imaging revealed a number of extended defects forming in the epilayer, and transmission electron microscopy imaging detailed a V-shaped pit defect formed by misoriented twin defects likely originating from a defect at or near the substrate surface. The Hall effect data (N-S = 2.81-3.1 x 10(17) cm(-3) and mu(H) = 81.5-103.5 cm(2)/V s), surface roughness (1.78-4.25 nm rms), and thermal conductivity measurements (19.3-19.8 W/m K) yielded comparable results among all samples, independent of epilayer thickness. These results suggested that even thicker, high quality epitaxial (010) beta-Ga2O3 could be grown via this technique, provided that the development of the observed extended defects can be mitigated. (c) 2025 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license(https://creativecommons.org/licenses/by/4.0/).

β-Ga 2 O 3 is a promising ultrawide-bandgap (4.8 eV) semiconductor material for power devices, with a high projected electric field strength of 6-8 MV/cm. The realization of β-Ga 2 O 3 power devices with high breakdown voltages ( V B ) and low reverse bias current ( J R ) is an ongoing route of investigation, with one line of interest being surface treatments to improve the interface between β-Ga 2 O 3 and a p-type heterojunction material or metal contact. This topic is particularly pertinent in device architectures utilizing BCl 3 plasma etching techniques, which are known to damage the β-Ga 2 O 3 surface. In this investigation, we performed solution processing aimed at mitigating surface defects resulting from BCl 3 plasma etching, while also examining the performance of identically solution-treated control samples without prior plasma etching. Specifically, we employed wet etches of (80 ℃) H 3 PO 4 , (70 ℃) TMAH, and room temperature 10:1 dilute HCl to samples with and without prior BCl 3 plasma exposure before fabricating NiO/β-Ga 2 O 3 PN heterojunction diodes and β-Ga 2 O 3 Schottky barrier diodes (SBDs). A control sample, untreated by solution, was also tested in each case. Five randomly selected devices were tested on each sample, and the averages are compared here. The results reveal that the averaged J R – taken at reverse bias of 100 V - was highest for the control samples both with (1.27 nA/cm 2 ) and without plasma treatment (1.76 nA/cm 2 ) in PN diodes, when compared with the samples treated with H 3 PO 4 (0.53 nA/cm 2 with, 0.52 nA/cm 2 without plasma treatment), TMAH (0.48 nA/cm 2 with, 0.71 nA/cm 2 without plasma treatment), and HCl (0.45 nA/cm 2 with, 0.40 nA/cm 2 without plasma treatment). For the SBDs the J R of the H 3 PO 4 treatment (0.96 μA/cm 2 with, 14.95 nA/cm 2 without plasma treatment) alone exceeded the J R of the control sample (1.39 nA/cm 2 with, 3.74 nA/cm 2 without plasma treatment). The TMAH-treated (0.60 nA/cm 2 ) and HCl-treated (0.45 nA/cm 2 ) SBDs exhibited similar values of J R for the plasma-treated samples, but diverged strongly for samples without plasma treatment (0.72 nA/cm 2 for TMAH, 1.48 nA/cm 2 for HCl). Notably the increase in J R for SBDs with H 3 PO 4 treatment was orders of magnitude, ranging from 10X without prior plasma-exposure to 1000X prior plasma-exposure for the SBD samples with H 3 PO 4 -treatment as compared with all others. There was not a significant and consistent advantage between TMAH and HCl, however the HCl average J R was less than that of TMAH in all devices except for the etched SBDs. Similarly for the averaged V B performance, the control sample had the lowest breakdown for both plasma etched (660 V) and unetched (600) PN diodes, with plasma-treated PN V B values of 928 V, 1518 V, and 1200 V for H 3 PO 4 , TMAH, and HCl-treated samples respectively, and unetched PN V B values of 1026 V, 1192 V, and 1468 V for H 3 PO 4 , TMAH, and HCl-treated samples respectively. Notably this set of randomly selected TMAH-treated PN diodes without plasma treatment included one strong outlier for V B of 380 V, without which the average V B was 1395 V. For the SBDs the H 3 PO 4 treatment did degrade the V B (306 V and 566 V with and without plasma-treatment, respectively) even below that of the control sample (778 V and 636 V with and without plasma-treatment, respectively). TMAH (836 V both with and without plasma-treatment) and HCl (864 V and 710 V with and without plasma-treatment, respectively) treated samples alternated in best performance both in averages and in the total spread of V B values, but consistently outperformed both the H 3 PO 4 treated and control samples. In conclusion, the 80 ℃ “warm” H 3 PO 4 -treatment used for these devices is not recommended in preparation of β-Ga 2 O 3 interfaces with NiO or metal anodes for PN and SBD devices, respectively. However, both the TMAH-treatment and HCl-treatment were found to improve the performance of PN heterojunction devices and SBDs, lowering the J R and raising the V B for β-Ga 2 O 3 surfaces both with and without prior exposure to BCl 3 plasma. Figure 1