In this paper, we validate the industry standard ASM-HEMT model for non-linear large-signal modeling of 140 nm GaN HEMT at X-band. An accurate model has been developed for fundamental, second-, and third-order harmonic frequency. Time-domain waveforms and dynamic load-line simulations from ASM-HEMT model are also validated against non-linear vector analyzer measurements. This is the first validation of ASM-HEMT model for harmonics and NVNA data. A good model agreement with measurements has been obtained.

This paper presents for the first time an investigation of the ASM-HEMT model large-signal accuracy across a wide range of operating frequencies. Comparisons between measured and simulated power sweeps are presented at 10, 20 and 30 GHz. Load-pull measurements and simulations are compared spanning the same frequency range. The large-signal simulations of a single ASM-HEMT model exhibit excellent agreement with all power measurements.

A key component for the realization of silicon-photonics is an integrated laser operating in the important communication band near 1.55 μm. One approach is through the use of GaSb-based alloys, which may be grown directly on silicon. In this study, silicon-compatible strained Ga0.8In0.2Sb/Al0.68In0.32Sb composite quantum well (CQW) lasers grown on GaSb substrates emitting at 1.55 μm have been developed and investigated in terms of their thermal performance. Variable temperature and high-pressure techniques were used to investigate the influence of device design on performance. These measurements show that the temperature dependence of the devices is dominated by carrier leakage from the QW region to the Xb minima of the Al0.35Ga0.65As0.03Sb0.97 barrier layers accounting for up to 43% of the threshold current at room temperature. Improvement in device performance may be possible through refinements in the CQW design, while carrier confinement may be improved by optimization of the barrier layer composition. This investigation provides valuable design insights for the monolithic integration of GaSb-based lasers on silicon.

We report the RF power results of Sc(Al,Ga)N/GaN high electron mobility transistors (HEMTs). We show dc, small-signal RF and load-pull performance at 30 GHz with two barrier alloys-a ternary of ScAlN and a quaternary of ScAlGaN. The active layers are grown by molecular beam epitaxy on a GaN-on-SiC template. The Sc(Al,Ga)N HEMTs with 120 nm gate length achieve transconductance >700 mS/mm and >70 GHz cutoff frequency. The quaternary ScAlGaN sample shows reduced current collapse during pulsed I-V and load-pull characterization. The ScAlGaN HEMT delivers 5.77 W/mm output power (VD = 20 V) and 47% power-added efficiency (VD = 15 V) when tuned for maximum power and efficiency, respectively.

Abstract Beta phase Gallium Oxide (BGO) is an emerging ultra-wide bandgap semiconductor with disruptive potential for ultra-low power loss, high-efficiency power applications. The critical field strength is the key enabling material parameter of BGO which allows sub-micrometer lateral transistor geometry. This property combined with ion-implantation technology and large area native substrates result in exceptionally low conduction power losses, faster power switching frequency and even radio frequency power. We present a review of BGO epitaxial materials and lateral field-effect transistors developments, highlight early achievements and discuss engineering solutions with power switching and radio frequency applications in mind.

We report the dc and RF performance of ScAlN/GaN high-electron-mobility transistors (HEMTs). The ScAlN/GaN material was epitaxially grown onto a GaN template on a 4-in 4H-SiC substrate by molecular beam epitaxy. The sheet resistance was measured to be 236 ± 4 $\Omega /\square $ across the wafer by the transfer length measurement. Selective area regrowth of highly doped GaN was implemented to reduce contact resistance ( ${R}_{C}$ ) as low as 0.1 $\Omega \cdot \textsf {mm}$ . HEMT devices with $\textsf {2}\times \textsf {150}\,\,\mu \text{m}$ gate width and 140-nm T-gate process show a maximum current density and a transconductance of 2.4 A/mm and 0.67 S/mm, respectively. The extrinsic small-signal gain was measured as a function of drain bias and gate length with extrinsic cutoff frequency and maximum oscillation frequency reported up to 88 and 91 GHz, respectively.

We report enhancement-mode beta-Ga2O3 (BGO) MOSFETs on a Si-doped homoepitaxial channel grown by molecular beam epitaxy. A gate recess process is used to partially remove the epitaxial channel under the 1-mu m gated region to fully deplete at V-GS = 0 V. BGO MOSFETs achieve drain current density near 40 mA/mm and I-ON/I-OFF ratio similar to 10(9) which is the highest reported for homoepitaxial normally-off BGO transistors. At V-GS = 0 V, a breakdown voltage of 198 and 505 V is achieved with the source-drain spacing of 3 and 8 mu m, respectively. The power switching figure of merits for dc conduction and dynamic switch losses meet or exceed the theoretical silicon limit and previously reported depletion-mode BGO transistors.

Si-doped Ga2O3 thin films were fabricated by pulsed laser deposition on semi-insulating (010) beta-Ga2O3 and (0001) Al2O3 substrates. Films deposited on beta-Ga2O3 showed single crystal, homoepitaxial growth as determined by high resolution transmission electron microscopy and x-ray diffraction. Corresponding films deposited on Al2O3 were mostly single phase, polycrystalline beta-Ga2O3 with a preferred (20 (1) over bar) orientation. An average conductivity of 732 S cm(-1) with a mobility of 26.5 cm(2) V-1 s(-1) and a carrier concentration of 1.74 x 10(20) cm(-3) was achieved for films deposited at 550 degrees C on beta-Ga2O3 substrates as determined by Hall-Effect measurements. Two orders of magnitude improvement in conductivity were measured using native substrates versus Al2O3. A high activation efficiency was obtained in the as-deposited condition. The high carrier concentration Ga2O3 thin films achieved by pulsed laser deposition enable application as a low resistance ohmic contact layer in beta-Ga2O3 devices.

We demonstrate a beta-Ga2O3 MOSFET with record-high transconductance (g(m)) of 21 mS/mm and extrinsic cutoff frequency (f(T)) and maximum oscillating frequency (f(max)) of 3.3 and 12.9 GHz, respectively, enabled by implementing a new highly doped ohmic cap layer with a sub-micron gate recess process. RF performance was further verified by CW Class-A power measurements with passive source and load tuning at 800 MHz, resulting in P-OUT, power gain, and power-added efficiency of 0.23 W/mm, 5.1 dB, and 6.3%, respectively. These preliminary results indicate potential for monolithic or heterogeneous integration of power switch and RF devices using beta-Ga2O3.

Beta-phase gallium oxide (Ga 2 O 3 ) is a promising wide bandgap semiconductor possessing a larger bandgap (~4.8 eV) and critical electric field strength (~8 MV/cm) than GaN and SiC [1]. Early metal-oxide-semiconductor field-effect transistors (MOSFETs) have shown promising depletion-mode operation with high critical field strength [2], high-current density [3] and high breakdown voltage [4]. On native substrates, enhancement-mode operation has been achieved with a gated unintentional doped channel [5] and fin-channels [6], the latter achieving 600-V normally-off breakdown voltage. However, both are limited to ~1 mA/mm or less. Here, we report a new enhancement-mode device achieved by gate recess with improved drain-current > 20 mA/mm and near 200-V breakdown for laterally scaled 3-μm source-drain distance (L sd ).

As a transparent conducting oxide with a large bandgap of ∼4.9 eV and associated large estimated critical electric field (E c ) strength of 8 MV/cm, β-Ga 2 O 3 (BGO) has been touted for its tremendous potential as a power switch. Power switch metrics such as Baliga's figure of merit (BFOM) estimating dc conduction losses and Huang's material figure of merit (HMFOM) incorporating dynamic switching losses are functions of E C 3 and E C respectively [1, 2]. BFOM for BGO is expected to exceed that of GaN by 400% and HMFOM for BGO is expected to be comparable to GaN. It can also be shown that for a given power loss during switching, the switch frequency (f) varies as E C 2 suggesting the potential of BGO power conversion in the GHz regime [1, 2]. The manufacturability and cost value proposition of BGO based on large area native substrate availability as shown by Huang's chip area manufacturing FOM (HCAFOM) indicate a disruptive cost advantage over GaN (330%). Additionally, the Johnson figure of merit (JFOM) representing the power-frequency product for RF amplification for BGO is similar to that of GaN indicating potential for integration of power conversion and RF applications in the same platform. Finally, Huang's high temperature figure of merit (HTFOM) shows that BGO has the lowest metric for all semiconductors compared here due to low thermal conductivity and high field strength. However, all wide bandgap power semiconductors, including diamond, face significant thermal engineering challenges relative to Si because of the inherent high energy densities of materials with large E c values. A summary of unipolar FET figure-of-merit comparisons for power semiconductors is shown in Table 1.

We review AFRL’s major device results in the fabrication of β-Ga2O3 MOSFETs over the past 2 years. This includes: (1) AFRL’s standard fabrication process, (2) improvement of current density, (3) improvement of contact resistance, (4) review of the critical field measurement and (5) review of enhancement mode operation of a β-Ga2O3 finFET.

A Sn-doped (100) β-Ga2O3 epitaxial layer was grown via metal-organic vapor phase epitaxy onto a single-crystal, Mg-doped semi-insulating (100) β-Ga2O3 substrate. Ga2O3-based metal-oxide-semiconductor field-effect transistors with a 2-μm gate length (LG), 3.4-μm source-drain spacing (LSD), and 0.6-μm gate-drain spacing (LGD) were fabricated and characterized. Devices were observed to hold a gate-to-drain voltage of 230 V in the OFF-state. The gate-to-drain electric field corresponds to 3.8 MV/cm, which is the highest reported for any transistor and surpassing bulk GaN and SiC theoretical limits. Further performance projections are made based on layout, process, and material optimizations to be considered in future iterations.

Sn-doped gallium oxide (Ga2O3) wrap-gate fin-array field-effect transistors (finFETs) were formed by top-down BCl3 plasma etching on a native semi-insulating Mg-doped (100) β-Ga2O3 substrate. The fin channels have a triangular cross-section and are approximately 300 nm wide and 200 nm tall. FinFETs, with 20 nm Al2O3 gate dielectric and ∼2 μm wrap-gate, demonstrate normally-off operation with a threshold voltage between 0 and +1 V during high-voltage operation. The ION/IOFF ratio is greater than 105 and is mainly limited by high on-resistance that can be significantly improved. At VG = 0, a finFET with 21 μm gate-drain spacing achieved a three-terminal breakdown voltage exceeding 600 V without a field-plate.

A GaN high electron mobility transistor monolithic microwave integrated circuit (MMIC) designer typically has to choose a device design either for high-gain millimeter-wave operation with a short gate length, or for high-power-density X-band operation with a much larger gate/field-plate structure. We provide the designer the option of incorporating two different devices by implementing a 0.14-mu m gate length GaN MMIC process capable of high-efficiency Ka-band operation while simultaneously achieving high power density in the same process flow. The key process enabler simply uses the capacitor top plate in the MMIC process as a field plate on the passivation layer. On two separate devices on the same chip using the same MMIC process flow, we demonstrate 7.7 W/mm at 35 GHz and V-DS = 30 V on a standard 4 x 65-mu m T-gated FET and then 12.5 W/mm at 10 GHz and VDS = 60 V on a 4 x 75-mu m T-gated FET by adding a field plate. These are the highest reported power densities achieved simultaneously at X-band and Ka-band in a single wideband GaN MMIC process.

Nonreciprocal magnetostatic wave propagation in micro-patterned Ni80Fe20 thin film has been investigated. The nonreciprocal devices consist of a set of coupled microstrip transmission lines acting as antennae on the top of the micro-patterned Ni80Fe20 films. The Ni80Fe20 films were structured into an array of rectangular prisms. Nonreciprocal wave propagation was observed in the patterned Ni80Fe20 film. Compared to the control device with a continuous Ni80Fe20 film, the micro-patterned Ni80Fe20 films led to a weaker non-reciprocity.

A wafer-scale comparison of HEMTs fabricated on as-grown GaN/Si and HEMTs fabricated in parallel on epitaxial layers from the GaN/Si growth integrated with a diamond substrate are presented. Diamond, which offers the highest room-temperature thermal conductivity of any bulk material, is being evaluated as a solution for thermal limitations observed in GaN-based devices. This paper will present electrical and thermal data collected at the wafer scale demonstrating the improvement realized by integration of a high-thermal-conductivity substrate. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The effects of proton irradiation energy on dc, small signal, and large signal rf characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) were investigated. AlGaN/GaN HEMTs were irradiated with protons at fixed fluence of 5 × 1015/cm2 and energies of 5, 10, and 15 MeV. Both dc and rf characteristics revealed more degradation at lower irradiation energy, with reductions of maximum transconductance of 11%, 22%, and 38%, and decreases in drain saturation current of 10%, 24%, and 46% for HEMTs exposed to 15, 10, and 5 MeV protons, respectively. The increase in device degradation with decreasing proton energy is due to the increase in linear energy transfer and corresponding increase in nonionizing energy loss with decreasing proton energy in the active region of the HEMTs. After irradiation, both subthreshold drain leakage current and reverse gate current decreased more than 1 order of magnitude for all samples. The carrier removal rate was in the range 121–336 cm−1 over the range of proton energies employed in this study.