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Hydrogen in β-Ga2O3 passivates shallow impurities and deep-level defects and can have a strong effect on conductivity. More than a dozen O–D vibrational lines have been reported for β-Ga2O3 treated with the heavy isotope of hydrogen, deuterium. To explain the large number of O–D centers that have been observed, the involvement of additional nearby defects and impurities has been proposed. A few O–H centers have been associated with specific impurities that were introduced intentionally during crystal growth. However, definitive assignments of O–H and O–D vibrational lines associated with important adventitious impurities, such as Si and Fe, have been difficult. A set of well-characterized Si-doped β-Ga2O3 epitaxial layers with different layer thicknesses has been deuterated and investigated by vibrational spectroscopy to provide new evidence for the assignment of a line at 2577 cm−1 to an OD–Si complex. The vibrational properties of several of the reported OD-impurity complexes are consistent with the existence of a family of defects with a V Ga 1 ic − D center at their core that is perturbed by a nearby impurity. [ABSTRACT FROM AUTHOR]

As gallium oxide-based heterojunction devices gain prominence, low-resistance contacts to aluminum gallium oxide material are of increasing importance for high performance and access to modulation doped layers. Here, the activation of ion-implanted silicon donors is investigated as a function of donor density from 5 × 1018 cm−3 to 1 × 1020 cm−3, activation anneal duration from 6 s to 600 s, and activation temperature from 900°C to 1140°C. Importantly, ohmic behavior was achievable across a reasonably wide process window at moderate to high doping concentrations. Specific contact resistance of 1 × 10−3 Ω cm2 and sheet resistance of 2.8 kΩ/□ were achieved for a 60 nm-deep 1 × 1020 cm−3 box implant after activation at 1000°C for 6 s with standard Ti/Au contacts. Under these conditions, an activation efficiency of 7% was observed with Hall mobility of ~32 cm2/Vs. Furthermore, we demonstrate a Schottky diode formed of implanted material with a rectification ratio > 106 and further confirm the Hall carrier density results using capacitance–voltage profiling analysis. Finally, we show the significant impact of anneal duration and the potential for deleterious over-annealing which reduces the active carrier density, mobility, and resultant material conductivity. [ABSTRACT FROM AUTHOR]

Platinum oxide (PtOx) Schottky contacts on degenerately doped β-Ga2O3 substrates show an increased barrier height of 85% and 64% when compared to nickel and platinum Schottky contacts, respectively. At low reverse voltage bias, the reverse leakage current of the PtOx Schottky barrier diodes was approximately 5–6 orders of magnitude lower than the reference evaporated Ni and Pt Schottky contacts. PtOx Schottky contacts were deposited using reactive sputtering on highly doped (8 × 1018 cm−3) ( 2 ¯ 01 ) β-Ga2O3:Sn substrates grown by the edge-defined film-fed growth (EFG) method. All Schottky metals were capped with evaporated Au. Capacitance–voltage and temperature-dependent current–voltage measurements were performed in order to extract the barrier height of the PtOx Schottky contact. Analysis of the diode ideality factors reveal that the PtOx Schottky contacts on highly doped β-Ga2O3 do not follow the thermionic field emission model and are impacted by inhomogeneous barrier height distribution. This work highlights the significance of PtOx Schottky contacts for β-Ga2O3-based power devices as a means for reducing leakage current. This work also holds relevance for low-voltage applications, where Schottky contacts for degenerately doped semiconductors can enable new electronic device applications. [ABSTRACT FROM AUTHOR]

The low thermal conductivity of β-Ga2O3 is a significant concern for maximizing the potential of this ultra-wide bandgap semiconductor as a power switching device technology. Here, we report on the use of nanocrystalline diamond (NCD) deposited via microwave plasma enhanced chemical vapor deposition (MP-CVD) as a top-side, device-level thermal management solution on a lateral β-Ga2O3 transistor. NCD was grown via MP-CVD on β-(AlxGa1−x)2O3/β-Ga2O3 heterostructures prior to the gate formation of the field-effect transistor. A reduced growth temperature of 400 °C and a SiNx barrier layer were used to protect the oxide semiconductors from etching in the MP-CVD H2 plasma environment. Raman spectroscopy showed a highly sp3-bonded NCD film was obtained at 400 °C, with grain size of about 50–100 nm imaged via atomic force microscopy. The incorporation of the NCD heat-spreading layer resulted in a β-(AlxGa1−x)2O3/β-Ga2O3 heterostructure field-effect transistor showing a decrease in the total thermal resistance at the gate by 42%. The fabrication process, including the NCD etch in the gate region, will need to be improved to minimize the impact of these processes on important device characteristics (i.e., drain current, threshold voltage, and leakage current). [ABSTRACT FROM AUTHOR]

This work demonstrates direct, rapid 2D thermal mapping measurement capabilities of the ultrawide bandgap semiconductor channel of lateral β-(AlxGa1−x)2O3/Ga2O3 transistors without sample contamination, long acquisition times, or sophisticated thermometry such as developing deep-ultra-violet compatible thermoreflectance systems. The temperature rise in the channel of a β-(Al0.21Ga0.79)2O3/Ga2O3 heterostructure field-effect transistor (HFET) was mapped using thermoreflectance imaging at 470 nm. First, the thermoreflectance response of the HFET channel was measured using a monochromator, revealing a maximum of the reflectance change around 470–480 nm. Thermoreflectance calibrations were then performed at 470 nm (peak of the reflectance change) and yielded an average thermoreflectance coefficient of 1.06 ± 0.07 × 10−4 K−1. Subsequent measurements of the device (power densities of 0.15–1.47 W/mm and gate-source voltage of 0 V) enabled extraction of a device-level thermal resistance of 51.1 mm·K/W in the channel at the drain-side of the gate. High-resolution, in situ scanning thermal microscopy measurements of the channel temperature rise show good agreement with and further support the thermoreflectance measurements. Finally, the thermal profile across the entire device length (metal electrodes and semiconductor channel) and width was simultaneously measured using thermoreflectance imaging at 470 nm, and the peak temperature rise was measured in the channel at the drain-side of the gate electrode. [ABSTRACT FROM AUTHOR]

Activation of ion‐implanted p‐type dopants in gallium nitride has demonstrated great progress utilizing high pressures to enable novel and traditional device architectures; however, such conditions consistently exhibit anomalously enhanced diffusion up to several microns in very short periods of time for device relevant concentrations. Here, this diffusion is shown to be modulated by unintentional hydrogen content within the anneal ambient and thus controllable by inclusion of a high‐temperature hydrogen getter. Furthermore, diffusion is also shown to be greatly suppressed using co‐implanted oxygen at low concentrations while simultaneously maintaining characteristics of p‐type material in photoluminescence. Subsequently, after annealing at 1300 °C for 30 min in 3.8 kbar of nitrogen pressure, the magnesium concentration in the diffusion tail is suppressed by 28% at 1–1.5 μm in depth using a hydrogen getter alone, which reduces hydrogen uptake by 45% and fully suppressed at >1 μm in depth using co‐implantation alone and further reduced with concurrent use of a hydrogen getter. Co‐implantation alone reduces the in‐diffused magnesium dose by 60% compared to reference samples. [ABSTRACT FROM AUTHOR]

Surface phonon polariton (SPhP) modes in polar semiconductors offer a low-loss platform for infrared nanophotonics and sensing. However, the efficient design of polariton-enhanced sensors requires a quantitative understanding of how to engineer the frequency and lifetime of SPhPs in nanophotonic structures. Here, we study organ-pipe resonances in 4H-SiC trenches as a prototype system for infrared sensing. We use a transmission line framework that accounts for the field distribution within the trench, accurately predicting mode frequency and lifetime when compared against finite element method (FEM) electromagnetic calculations. Accounting for the electric field profile across the gap is critical in our model to accurately predict mode frequencies, quality factor (Q factor), and reflectance, outperforming previous circuit models developed in the literature. Beyond structural simulation, our model can provide insights into the frequency ranges in the Reststrahlen band where enhanced sensor activity should be present. The radiative lifetime is significantly enlarged close to the longitudinal optic phonon, restricting sensor efficiency at this wavelength range. This pushes the optimal frequency for sensing closer to the center of the Reststrahlen band than might be naively expected. This model ultimately demonstrates the primary challenge of designing SPhP-based sensors: only a relatively narrow region of the Reststrahlen band offers efficient sensing, guiding future designs for infrared spectroscopy., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)