Showing papers by "Stephen J. Pearton published in 2018"

A review of Ga2O3 materials, processing, and devices

Abstract: Gallium oxide (Ga2O3) is emerging as a viable candidate for certain classes of power electronics, solar blind UV photodetectors, solar cells, and sensors with capabilities beyond existing technologies due to its large bandgap. It is usually reported that there are five different polymorphs of Ga2O3, namely, the monoclinic (β-Ga2O3), rhombohedral (α), defective spinel (γ), cubic (δ), or orthorhombic (e) structures. Of these, the β-polymorph is the stable form under normal conditions and has been the most widely studied and utilized. Since melt growth techniques can be used to grow bulk crystals of β-GaO3, the cost of producing larger area, uniform substrates is potentially lower compared to the vapor growth techniques used to manufacture bulk crystals of GaN and SiC. The performance of technologically important high voltage rectifiers and enhancement-mode Metal-Oxide Field Effect Transistors benefit from the larger critical electric field of β-Ga2O3 relative to either SiC or GaN. However, the absence of clear demonstrations of p-type doping in Ga2O3, which may be a fundamental issue resulting from the band structure, makes it very difficult to simultaneously achieve low turn-on voltages and ultra-high breakdown. The purpose of this review is to summarize recent advances in the growth, processing, and device performance of the most widely studied polymorph, β-Ga2O3. The role of defects and impurities on the transport and optical properties of bulk, epitaxial, and nanostructures material, the difficulty in p-type doping, and the development of processing techniques like etching, contact formation, dielectrics for gate formation, and passivation are discussed. Areas where continued development is needed to fully exploit the properties of Ga2O3 are identified.

Perspective: Ga2O3 for ultra-high power rectifiers and MOSFETS

Abstract: Gallium oxide (Ga2O3) is emerging as a viable candidate for certain classes of power electronics with capabilities beyond existing technologies due to its large bandgap, controllable doping, and the availability of large diameter, relatively inexpensive substrates. These applications include power conditioning systems, including pulsed power for avionics and electric ships, solid-state drivers for heavy electric motors, and advanced power management and control electronics. Wide bandgap (WBG) power devices offer potential savings in both energy and cost. However, converters powered by WBG devices require innovation at all levels, entailing changes to system design, circuit architecture, qualification metrics, and even market models. The performance of high voltage rectifiers and enhancement-mode metal-oxide field effect transistors benefits from the larger critical electric field of β-Ga2O3 relative to either SiC or GaN. Reverse breakdown voltages of over 2 kV for β-Ga2O3 have been reported, either with or without edge termination and over 3 kV for a lateral field-plated Ga2O3 Schottky diode on sapphire. The metal-oxide-semiconductor field-effect transistors fabricated on Ga2O3 to date have predominantly been depletion (d-mode) devices, with a few demonstrations of enhancement (e-mode) operation. While these results are promising, what are the limitations of this technology and what needs to occur for it to play a role alongside the more mature SiC and GaN power device technologies? The low thermal conductivity might be mitigated by transferring devices to another substrate or thinning down the substrate and using a heatsink as well as top-side heat extraction. We give a perspective on the materials’ properties and physics of transport, thermal conduction, doping capabilities, and device design that summarizes the current limitations and future areas of development. A key requirement is continued interest from military electronics development agencies. The history of the power electronics device field has shown that new technologies appear roughly every 10-12 years, with a cycle of performance evolution and optimization. The older technologies, however, survive long into the marketplace, for various reasons. Ga2O3 may supplement SiC and GaN, but is not expected to replace them.

Point defect induced degradation of electrical properties of Ga2O3 by 10 MeV proton damage

Abstract: Deep electron and hole traps in 10 MeV proton irradiated high-quality β-Ga2O3 films grown by Hydride Vapor Phase Epitaxy (HVPE) on bulk β-Ga2O3 substrates were measured by deep level transient spectroscopy with electrical and optical injection, capacitance-voltage profiling in the dark and under monochromatic irradiation, and also electron beam induced current. Proton irradiation caused the diffusion length of charge carriers to decrease from 350–380 μm in unirradiated samples to 190 μm for a fluence of 1014 cm−2, and this was correlated with an increase in density of hole traps with optical ionization threshold energy near 2.3 eV. These defects most likely determine the recombination lifetime in HVPE β-Ga2O3 epilayers. Electron traps at Ec-0.75 eV and Ec-1.2 eV present in as-grown samples increase in the concentration after irradiation and suggest that these centers involve native point defects.

Structure and vibrational properties of the dominant O-H center in β-Ga2O3

Abstract: Hydrogen has a strong influence on the electrical properties of transparent conducting oxides where it can give rise to shallow donors and can passivate deep compensating defects. We have carried out infrared absorption experiments on H- and D-doped β-Ga2O3 that involve temperature- and polarization-dependent effects as well as relative H- and D-concentrations to probe the defect structures that hydrogen can form. The results of analysis of these data, coupled with detailed theoretical calculations, show that the dominant O-H vibrational line observed at 3437 cm−1 for hydrogenated Ga2O3 is due to a relaxed VGa-2H center.

Ga2O3 Schottky rectifiers with 1 ampere forward current, 650 V reverse breakdown and 26.5 MW.cm-2 figure-of-merit

Abstract: A key goal for Ga2O3 rectifiers is to achieve high forward currents and high reverse breakdown voltages. Field-plated β-Ga2O3 Schottky rectifiers with area 0.01 cm2, fabricated on 10 μm thick, lightly-doped drift regions (1.33 x 1016 cm-3) on heavily-doped (3.6 x 1018 cm-3) substrates, exhibited forward current density of 100A.cm-2 at 2.1 V, with absolute current of 1 A at this voltage and a reverse breakdown voltage (VB) of 650V. The on-resistance (RON) was 1.58 x 10-2 Ω.cm2, producing a figure of merit (VB2/RON) of 26.5 MW.cm-2. The Schottky barrier height of the Ni was 1.04 eV, with an ideality factor of 1.02. The on/off ratio was in the range 3.3 x 106 - 5.7 x 109 for reverse biases between 5 and 100V. The reverse recovery time was ∼30 ns for switching from +2V to -5V. The results show the capability of β-Ga2O3 rectifiers to achieve exceptional performance in both forward and reverse bias conditions.

Effect of 1.5 MeV electron irradiation on β-Ga2O3 carrier lifetime and diffusion length

Abstract: The influence of 1.5 MeV electron irradiation on minority transport properties of Si doped β-Ga2O3 vertical Schottky rectifiers was observed for fluences up to 1.43 × 1016 cm−2. The Electron Beam-Induced Current technique was used to determine the minority hole diffusion length as a function of temperature for each irradiation dose. This revealed activation energies related to shallow donors at 40.9 meV and radiation-induced defects with energies at 18.1 and 13.6 meV. Time-resolved cathodoluminescence measurements showed an ultrafast 210 ps decay lifetime and reduction in carrier lifetime with increased irradiation.

Defects responsible for charge carrier removal and correlation with deep level introduction in irradiated β-Ga2O3

Abstract: Carrier removal rates and electron and hole trap densities in β-Ga2O3 films grown by hydride vapor phase epitaxy (HVPE) and irradiated with 18 MeV α-particles and 20 MeV protons were measured and compared to the results of modeling. The electron removal rates for proton and α-radiation were found to be close to the theoretical production rates of vacancies, whereas the concentrations of major electron and hole traps were much lower, suggesting that the main process responsible for carrier removal is the formation of neutral complexes between vacancies and shallow donors. There is a concurrent decrease in the diffusion length of nonequilibrium charge carriers after irradiation, which correlates with the increase in density of the main electron traps E2* at Ec − (0.75–0.78) eV, E3 at Ec − (0.95–1.05) eV, and E4 at Ec − 1.2 eV. The introduction rates of these traps are similar for the 18 MeV α-particles and 20 MeV protons and are much lower than the carrier removal rates.

Diffusion length of non-equilibrium minority charge carriers in β-Ga2O3 measured by electron beam induced current

Abstract: The spatial distribution of electron-hole pair generation in β-Ga2O3 as a function of scanning electron microscope (SEM) beam energy has been calculated by a Monte Carlo method. This spatial distribution is then used to obtain the diffusion length of charge carriers in high-quality epitaxial Ga2O3 films from the dependence of the electron beam induced current (EBIC) collection efficiency on the accelerating voltage of a SEM. The experimental results show, contrary to earlier theory, that holes are mobile in β-Ga2O3 and to a large extent determine the diffusion length of charge carriers. Diffusion lengths in the range 350–400 nm are determined for the as-grown Ga2O3, while processes like exposing the samples to proton irradiation essentially halve this value, showing the role of point defects in controlling minority carrier transport. The pitfalls related to using other popular EBIC-based methods assuming a point-like excitation function are demonstrated. Since the point defect type and the concentration i...

Effect of surface treatments on electrical properties of β-Ga2O3

Abstract: The effect of various combinations of gaseous (ultraviolet/O3), liquid (HCl, buffered oxide etch, and H2O2), or plasma (CF4 and O2) treatments of the surface of β-Ga2O3 was quantified by current–voltage and capacitance–voltage measurements of rectifier structures. Plasma exposure (13.56 MHz, 24 kW/cm2) always led to significant degradation of the surface, as evidenced by large increases in rectifier reverse current and ideality factor (from 1.01 in control samples to ∼3.8 in plasma exposed samples, indicating additional defect-related carrier transport mechanisms) and lowering of the Schottky barrier height (from 1.21 eV in control samples to 0.75–0.86 eV in plasma exposed samples) and diode rectification ratio, with degraded reverse recovery characteristics. This was true of both CF4 and O2, even though it is known that fluorine incorporation in the near-surface leads to donor compensation and an increase in barrier height. Damage from the plasma exposure was not fully recovered by annealing at 500 °C. The O3 and liquid chemical cleans did lead to reduced reverse current in rectifiers, with no measurable decrease in barrier height, increase in ideality factor, or degradation of reverse recovery characteristics. Surfaces treated in this manner did not significantly change for anneals up to 500 °C; however, the Ni/Au contacts already show degradation after annealing at 350 °C.

Two-Dimensionally Layered p-Black Phosphorus/n-MoS2/p-Black Phosphorus Heterojunctions

Abstract: Layered heterojunctions are widely applied as fundamental building blocks for semiconductor devices. For the construction of nanoelectronic and nanophotonic devices, the implementation of two-dimensional materials (2DMs) is essential. However, studies of junction devices composed of 2DMs are still largely focused on single p–n junction devices. In this study, we demonstrate a novel pnp double heterojunction fabricated by the vertical stacking of 2DMs (black phosphorus (BP) and MoS2) using dry-transfer techniques and the formation of high-quality p–n heterojunctions between the BP and MoS2 in the vertically stacked BP/MoS2/BP structure. The pnp double heterojunctions allowed us to modulate the output currents by controlling the input current. These results can be applied for the fabrication of advanced heterojunction devices composed of 2DMs for nano(opto)electronics.

Recombination properties of dislocations in GaN

Abstract: The recombination activity of threading dislocations in n-GaN with different dislocation densities and different doping levels was studied using electron beam induced current (EBIC). The recombination velocity on a dislocation, also known as the dislocation recombination strength, was calculated. The results suggest that dislocations in n-GaN giving contrast in EBIC are charged and surrounded by a space charge region, as evidenced by the observed dependence of dislocation recombination strength on dopant concentration. For moderate (below ∼108 cm−2) dislocation densities, these defects do not primarily determine the average diffusion length of nonequilibrium charge carriers, although locally, dislocations are efficient recombination sites. In general, it is observed that the effect of the growth method [standard metalorganic chemical vapor deposition (MOCVD), epitaxial lateral overgrowth versions of MOCVD, and hydride vapor phase epitaxy] on the recombination activity of dislocations is not very pronounce...

Zika virus detection using antibody-immobilized disposable cover glass and AlGaN/GaN high electron mobility transistors

Abstract: Zika virus detection was demonstrated using antibody-functionalized cover glasses externally connected to the gate electrode of an AlGaN/GaN high electron mobility transistor (HEMT). A pulsed bias voltage of 0.5 V was applied to an electrode on the region of the cover glass region functionalized with antibody, and the resulting changes of drain current of the HEMT were employed to determine the presence of Zika virus antigen concentration ranging from 0.1 to 100 ng/ml. The dynamic and static drain current changes as a function of Zika virus concentration were modeled with a spring-like elastic relaxation model and the Langmuir extension model, respectively. Excellent fits to the data were found with relaxation time constants of antibody and antigen molecules in the range of 11 μs and 0.66–24.4 μs, respectively, for the concentration range investigated. The ratio of antibody bound with antigen to the total available antibody on the functionalized contact window was in the range of 0.013–0.84 for the Zika antigen concentration range of 0.1–100 ng/ml. Since the HEMT is not exposed to the bio-solution, it can be used repeatedly. The functionalized glass is the only disposable part in the detection system, showing the potential of this approach for hand-held, low cost sensor packages for point-of-care applications.

Effects of fluorine incorporation into β-Ga2O3

Abstract: β-Ga2O3 rectifiers fabricated on lightly doped epitaxial layers on bulk substrates were exposed to CF4 plasmas. This produced a significant decrease in Schottky barrier height relative to unexposed control diodes (0.68 eV compared to 1.22 eV) and degradation in ideality factor (2.95 versus 1.01 for the control diodes). High levels of F (>1022 cm−3) were detected in the near-surface region by Secondary Ion Mass Spectrometry. The diffusion of fluorine into the Ga2O3 was thermally activated with an activation energy of 1.24 eV. Subsequent annealing in the range 350–400 °C brought recovery of the diode characteristics and an increase in barrier height to a value larger than in the unexposed control diodes (1.36 eV). Approximately 70% of the initial F was removed from the Ga2O3 by 400 °C, with the surface outgas rate also being thermally activated with an activation energy of 1.23 eV. Very good fits to the experimental data were obtained by integrating physics of the outdiffusion mechanisms into the Florida Object Oriented Process Simulator code and assuming that the outgas rate from the surface was mediated through fluorine molecule formation. The fluorine molecule forward reaction rate had an activation energy of 1.24 eV, while the reversal rate of this reaction had an activation energy of 0.34 eV. The net carrier density in the drift region of the rectifiers decreased after CF4 exposure and annealing at 400 °C. The data are consistent with a model in which near-surface plasma-induced damage creates degraded Schottky barrier characteristics, but as the samples are annealed, this damage is removed, leaving the compensation effect of Si donors by F− ions. The barrier lowering and then enhancement are due to the interplay between surface defects and the chemical effects of the fluorine.

10 MeV proton damage in β-Ga2O3 Schottky rectifiers

Abstract: The electrical performance of vertical geometry Ga2O3 rectifiers was measured before and after 10 MeV proton irradiation at a fixed fluence of 1014 cm−2, as well as subsequent annealing up to 450 °C. Point defects introduced by the proton damage create trap states that reduce the carrier concentration in the Ga2O3, with a carrier removal rate of 235.7 cm−1 for protons of this energy. The carrier removal rates under these conditions are comparable to GaN-based films and heterostructures. Even annealing at 300 °C produces a recovery of approximately half of the carriers in the Ga2O3, while annealing at 450 °C almost restores the reverse breakdown voltage. The on/off ratio of the rectifiers was severely degraded by proton damage and this was only partially recovered by 450 °C annealing. The minority carrier diffusion length decreased from ∼340 nm in the starting material to ∼315 nm after the proton irradiation. The reverse recovery characteristics showed little change with values in the range 20–30 ns before...

AlGaN/GaN Heterostructure Based Schottky Diode Sensors with ZnO Nanorods for Environmental Ammonia Monitoring Applications

Abstract: AlGaN/GaN heterostructure Schottky diodes with ZnO nanorod functionalization are shown to be capable of detecting NH3 balanced with air at a concentration of ∼0.3 ppm at 25◦C and ∼0.1ppm at 300◦C. The diodes show reproducible current response to repeated cycling of the NH3 exposure at all temperatures in this range. The diode current at fixed voltage decreased upon exposure to the NH3, which is opposite to what occurs with exposure to hydrogen. This suggests the detection mechanism involves reaction of ammonia with oxygen species on the ZnO nanorods, increasing the negative charge on the interface with AlGaN. The detection sensitivity displayed an activation energy of 0.071 eV and increased monotonically with ammonia concentration at all temperatures, from 3.36% (25◦C) to 12.59% (300◦C) for 2 ppm at a voltage of 5 V. The diodes could detect ammonia for either polarity applied bias. The absolute current change and sensitivity upon exposure to ammonia increased with measurement temperature. © The Author(s) 2018. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0041807jss]

Hydrogen sensing characteristics of Pt Schottky diodes on (201) and (010) Ga2O3 single crystals

Abstract: 1Department of Chemical Engineering, Dankook University, Yongin 16890, South Korea 2Department of Chemical Engineering, Korea University, Seoul 02841, South Korea 3Department of Chemical Engineering, University of Florida, Gainesville, Florida 32611, USA 4Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611, USA 5School of Materials Science and Engineering, Hongik University, Sejong 30016, South Korea

Valence band offsets for CuI on (-201) bulk Ga2O3 and epitaxial (010) (Al0.14Ga0.86)2O3

Abstract: Thin films of copper iodide (CuI) were grown on (-201) bulk Ga2O3 and (010) epitaxial (Al0.14Ga0.86)2O3 using a copper film iodination reaction method. The valence band offsets for these heterostructures were measured by X-ray photoelectron spectroscopy (XPS). High resolution XPS data of the O 1s peak and onset of elastic losses were used to establish the (Al0.14Ga0.86)2O3 bandgap to be 5.0 ± 0.30 eV. The valence band offsets were −0.25 eV ± 0.07 eV and 0.05 ± 0.02 eV for CuI on Ga2O3 or (Al0.14Ga0.86)2O3, respectively. The respective conduction band offsets were 1.25 ± 0.25 eV for Ga2O3 and 1.85 ± 0.35 eV for (Al0.14Ga0.86)2O3. Thus, there is a transition from type-II to type-I alignment as Al is added to β-Ga2O3. The low valence band offsets are ideal for hole transport across the heterointerfaces.

Effect of proton irradiation energy on SiNx/AlGaN/GaN metal-insulator semiconductor high electron mobility transistors

Abstract: The effects of proton irradiation energy on the electrical properties of SiNx/AlGaN/GaN metal-insulator semiconductor high electron mobility transistors (MISHEMTs) using in situ grown silicon nitride as the gate dielectric were studied The SiNx/AlGaN/GaN MISHEMT devices were irradiated with protons at energies of 5, 10, or 15 MeV at a fixed fluence of 25 × 1014 cm−2 The largest amount of device degradation was shown in the samples irradiated with the lowest irradiation energy of 5 MeV The DC saturation current was reduced by 104%, 32%, and 05% for MISHEMTs irradiated with proton energies of 5, 10, and 15 MeV, respectively Device performance degradation was more pronounced in the irradiated samples under high-frequency operation At a frequency of 100 kHz, the percent saturation drain current reduction at a gate voltage of 3 V was 40%, 19%, and 17% after proton irradiation at 5, 10, and 15 MeV, respectively The carrier removal rates for the MISHEMT devices were in the range of 21–144 cm−1 for the proton irradiation energies studied The measured DC degradation and carrier removal rates are lower than the values reported for AlGaN/GaN metal-gate high electron mobility transistor devices irradiated at similar conditions, which can be attributed to the SiNx insulating layer reducing the total damage on the AlGaN surfaceThe effects of proton irradiation energy on the electrical properties of SiNx/AlGaN/GaN metal-insulator semiconductor high electron mobility transistors (MISHEMTs) using in situ grown silicon nitride as the gate dielectric were studied The SiNx/AlGaN/GaN MISHEMT devices were irradiated with protons at energies of 5, 10, or 15 MeV at a fixed fluence of 25 × 1014 cm−2 The largest amount of device degradation was shown in the samples irradiated with the lowest irradiation energy of 5 MeV The DC saturation current was reduced by 104%, 32%, and 05% for MISHEMTs irradiated with proton energies of 5, 10, and 15 MeV, respectively Device performance degradation was more pronounced in the irradiated samples under high-frequency operation At a frequency of 100 kHz, the percent saturation drain current reduction at a gate voltage of 3 V was 40%, 19%, and 17% after proton irradiation at 5, 10, and 15 MeV, respectively The carrier removal rates for the MISHEMT devices were in the range of 21–144 cm−1 for the

Trapping Phenomena in InAlN/GaN High Electron Mobility Transistors

Abstract: Electron trapping-detrapping phenomena were studied for InAlN/GaN high electron mobility transistors (HEMTs) by drain currentdrain voltage static and pulsed current voltage (I-V) characteristics, gate current I-Vs, transfer characteristic measurements, current deep level transient spectroscopy (CDLTS) with gate voltage pulsing, and by drain current transient measurements following both drain and gate voltage steps. The electron trapping processes are temperature activated with activation energies of 1.1 eV for drain voltage steps and 1 eV and 0.75 eV for gate voltage steps. Detrapping processes show activation energies 0.9 eV and (0.7–0.75) eV. Drain current transients are accurately described by the sum of two stretched exponents. The amplitudes of CDLTS peaks corresponding to electron trapping and electron detrapping processes show la ogarithmic dependence on the width of the injection pulse, indicating that the traps are related to dislocations. © 2018 The Electrochemical Society. [DOI: 10.1149/2.0131802jss]

Radiation damage in Ga2O3

Abstract: The β-phase is the most common of the different polymorphs of Ga2O3 and is stable through the whole temperature range up to the melting point. β-Ga2O3 has a C-centered monoclinic unit cell with space group C2/m. Large diameter bulk crystals of this material are commercially available and the wide bandgap makes it promising for both power electronics and solar-blind UV detection. In some applications, it is desirable that the Ga2O3 have a significant degree of radiation hardness. There are now some initial reports of the effect of proton, electron, gamma ray and neutron irradiation of n-type β-Ga2O3 rectifiers, and UV photodetectors under conditions relevant to low Earth orbit of satellites containing these types of devices. The carrier removal rates for proton, electron, and neutron irradiation are found to comparable to those in GaN of similar doping levels for the same types of fluences. The main defect created in Ga2O3 by proton irradiation has been identified as a Ga vacancy with two hydrogens attached. Neutron irradiation produces a dominant state with an ionization level near EC—1.88 eV.

Moisture Insensitive PMMA Coated Pt-AlGaN/GaN Diode Hydrogen Sensor and Its Thermal Stability

Abstract: Poly(methyl methacrylate) (PMMA) encapsulated Pt-AlGaN/GaN Schottky diodes show highly sensitive (100 ppm, 0.01% by volume) room temperature detection of hydrogen and are insensitive to the presence of water in the sensing ambient. These diodes show no physical degradation or loss of sensitivity when repeatedly cycled (50 x, 1 min hold at each temperature) between 25–100◦C. There is complete selectivity for hydrogen sensing over other gases, including CO, CO2, NO2, O2 and CH4. The PMMA encapsulation provides an effective and robust barrier to moisture, greatly increasing the range of environments in which the sensors can be used. © The Author(s) 2018. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.002107jss]

Thermally stable ammonia gas sensor using ZnO-functionalized AlGaN/GaN heterostructure transistor

Abstract: Methods and apparatuses for detecting ammonia are disclosed. A sensor can include a transistor having a gate, a drain, and a source. A layer of ammonia detecting material can be functionally attached to the transistor. The ammonia detecting material can be zinc oxide (ZnO) nanorods, which effectively functionalize the transistor by changing the amount of current that flows through the gate when a voltage is applied. Alternatively, or in addition to ZnO nanorods, films or nanostructure type metal oxides including TiO2, ITO, ZnO, WO 3 and AZO can be used. The transistor is preferably a high electron mobility transistor (HEMT).

Effect of alpha-particle irradiation dose on SiNx/AlGaN/GaN metal–insulator semiconductor high electron mobility transistors

Abstract: The effects of 18 MeV alpha particle irradiation dose on the electrical properties of SiNx/AlGaN/GaN metal insulator semiconductor high electron mobility transistors (MISHEMTs) using in situ grown silicon nitride as the gate dielectric were investigated. The MISHEMT devices were irradiated with alpha particles at doses of 1 × 1012 or 1 × 1013 cm−2 at a fixed energy of 18 MeV. Device performance degradation was more prominent for the irradiated samples under high frequency operation. At a frequency of 100 kHz and gate voltage pulsed from −6 to 3 V, the saturation drain current reduction was 32% and 41% after alpha irradiation doses of 1 × 1012 and 1 × 1013 cm−2, respectively. The drain current reduction at 100 kHz also depended on the duty cycle. At higher duty cycles, the drain current reduction was less severe. The calculated carrier removal rates were in the range of 2062–2175 cm−1 for the alpha doses studied. The results demonstrate the capability of AlGaN/GaN MISHEMTs in environments where resilience ...

Radiation and process-induced damage in Ga2O3

Abstract: Ga2O3 is gaining attention for high breakdown electronics. The β-polymorph is air-stable, has a wide bandgap (~4.6 eV) and is available in both bulk and epitaxial form. Different types of power diodes and transistors fabricated on Ga2O3 have shown impressive performance. Etching processes for Ga2O3 are needed for patterning for mesa isolation, threshold adjustment in transistors, thinning of nano-belts and selective area contact formation. Electrical damage in the near-surface region was found through barrier height changes of Schottky diodes on the etched surface. The damage is created by energetic ion bombardment, but may also consist of changes to near-surface stoichiometry through loss of lattice elements or deposition of etch residues. Annealing at 450°C removes this damage. We also discuss recent results on damage introduction by proton and electron irradiation. In this case, the carrier removal rates are found to be similar to those reported for GaN under similar conditions of dose and energy of the radiation.

Water-insensitive gas sensor using polymer-encapsulated Pt—AlGaN/GaN diodes

Abstract: A hydrogen sensor can include a substrate, an Ohmic metal disposed on the substrate, a nitride layer disposed on the substrate and having a first window exposing the substrate, a Schottky metal placed in the first window and disposed on the substrate, a final metal disposed on the nitride layer and the Schottky metal and having a second window exposing the Schottky metal, and a polymethyl-methacrylate (PMMA) layer encapsulating the second window. The PMMA layer can fill the second window and be in contact with the Schottky metal.