In this letter, we report record power added efficiency (PAE) on a vector load-pull system at 220 GHz of 31.3% +/- 0.8% for an indium phosphide (InP) heterojunction bipolar transistor (HBT) and 26.9% +/- 1.4% for an InP high-electron mobility transistor (HEMT) with minimal measurement error. We first minimize measurement error by using on-chip shielded multiline thru-reflect-line (mTRL) standards to eliminate unwanted modes of propagation and by using WR4.3 probes that have minimal crosstalk coupling. We then demonstrate crosstalk mitigation by calibrating the load-pull data using a conventional eight-term mTRL and a 16-term crosstalk methods, resulting only in a 0.4% error in peak PAE. We quantify the remaining measurement errors due to absolute power and waveguide calibration repeatability as well as the on-wafer errors in the probe placement and error in the 50 Omega reference system. A +/- 0.1% uncertainty in peak PAE was obtained from repeated waveguide and power calibrations. The on-wafer measurement error resulted in a peak PAE uncertainty of +/- 0.8% and +/- 1.4% for the HBT and HEMT devices, respectively.

We demonstrate the effect of BaTiO3 integration on scaled BaTiO3/Al2O3/In0.04Al0.70GaN0.26/GaN metal–insulator–semiconductor high electron mobility transistors (MISHEMTs). We find that sputter processing and device fabrication decreases barrier thickness and mobility of the HEMT structure, and the inclusion of a GaN cap recovers the device performance. We then employ a 20-element lumped small signal equivalent circuit model to assess the impact of BaTiO3 integration on scaled devices. Finally, a demonstration of devices with various barrier and dielectric designs shows that BaTiO3 gate dielectric improves Vds and gate drive handling of devices, decreased the negative slope of the gain in the compression regime due to a more uniform field profile, and enables higher output power (Pout). It is shown that through the integration of BaTiO3 and a GaN cap, the output power of the devices increases from 1.42 W/mm to 5.77 W/mm.

We evaluate the accuracy of small-signal on-wafer device characterization in the sub-THz frequency range when employing conventional and advanced calibration methods with state-of-the-art design of on-chip standards. We report that major discrepancies resulting from an interlaboratory comparison experiment are mainly attributed to the influence of microwave probes. When performing conventional multiline thru-reflect-line (mTRL) calibrations with six different models of probe from 140 to 325 GHz, we observe significant variations in the measured scattering-parameters (S-parameters) and show that probes made by various manufacturers induce disparate crosstalk responses that vary between -70 and -15 dB on open-open standards. After applying a crosstalk correction approach as a second-tier calibration, we obtain significantly better agreement between the RF performance of the same heterojunction bipolar transistor (HBT) measured with two different probe models. While the difference between the maximum stable gain (MSG) reaches 1.8 dB at 210 GHz after applying a conventional mTRL calibration, we reduce the error to similar to 0.5 dB after crosstalk correction. This study shows that crosstalk correction methods must be implemented in the sub-THz frequency range to accurately estimate the RF performance of active devices and circuits.

High temperature (HT) electronics applica-tions will require the development of a broad range ofdevices made using different materials. Among thesedevices, high-electron mobility transistors (HEMTs) madewith GaN and its alloys are attractive for high-power radiofrequency (RF) applications. In this manuscript, we testedAlGaN/GaN HEMT devices having similar to 140-nm gate length atdifferent temperatures up to 500 degrees C. Devices were fab-ricated using Air Force Research Laboratory's (AFRL's)140-nmT-gate process technology. The performancedegradation measured in different devices was analyzed byconsidering changes in different device parameters and byusing appropriate device physics. Cross-sectional materi-als characterization using scanning transmission electronmicroscopy (STEM) and electron energy loss spectroscopy(EELS) was performed to understand the origin of perfor-mance degradation. This understanding will allow us todesign a sub-mu m GaN-based process technology compat-ible with HT RF applications

High temperature (HT) electronics applications will require the development of a broad range of devices made using different materials. Among these devices, high-electron mobility transistors (HEMTs) made with GaN and its alloys are attractive for high-power radio frequency (RF) applications. In this manuscript, we tested AlGaN/GaN HEMT devices having <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula> 140-nm gate length at different temperatures up to 500 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> C. Devices were fabricated using Air Force Research Laboratory’s (AFRL’s) 140-nm <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> -gate process technology. The performance degradation measured in different devices was analyzed by considering changes in different device parameters and by using appropriate device physics. Cross-sectional materials characterization using scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) was performed to understand the origin of performance degradation. This understanding will allow us to design a sub- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> m GaN-based process technology compatible with HT RF applications.

This manuscript presents our recent findings from small signal RF measurements of AlGaN/GaN high-electron-mobility transistors (HEMTs) at different temperatures. We will discuss the temperature-dependent variations of key RF device performance parameters, including extrinsic cutoff frequency $(f_{T})$ , maximum gain frequency $(f_{max}$ ), unilateral power gain (UPG), and maximum stable gain (MSG).

Development of high-temperature compatible electronic devices is desired for several applications. Electronic devices made with wide bandgap and ultra-wide bandgap materials are suitable for these high temperature applications. In this article, we presented high temperature device data obtained from p-Ga203 field-effect transistors (FETs) and AIGaN/GaN high-electron mobility transistors (HEMTs) at temperatures up to 500 oC, We discussed device details, systematically analyzed the electrical data by considering insights obtained from materials characterization, and explained the variation in device parameters (such as transconductance, threshold voltage, contact resistance, gate leakage) with temperature and time.

Development of high-temperature compatible electronic devices is desired for several applications. Electronic devices made with wide bandgap and ultra-wide bandgap materials are suitable for these high temperature applications. In this article, we presented high temperature device data obtained from p-Ga203 field-effect transistors (FETs) and AIGaN/GaN high-electron mobility transistors (HEMTs) at temperatures up to 500 oC, We discussed device details, systematically analyzed the electrical data by considering insights obtained from materials characterization, and explained the variation in device parameters (such as transconductance, threshold voltage, contact resistance, gate leakage) with temperature and time.

Here, we investigate the use of few-layer metal organic chemical vapor deposition (MOCVD) grown BN as a two-dimensional buffer layer for plasma enhanced atomic layer deposition (PE-ALD) of Al 2 O 3 on graphene for top gated field effect transistors (FETs). The reactive nature of PE-ALD enables deposition of thin (2 nm) dielectrics directly on graphene and other two-dimensional materials without the need for a seed or functionalization layer; however, this also leads to significant oxidation of the graphene layer as observed by Raman. In FETs, we find this oxidation destroys conductivity in the graphene channel. By transferring thin (1.6 nm) MOCVD BN layers on top of graphene channels prior to PE-ALD, the graphene is protected from oxidation enabling BN/Al 2 O 3 layers as thin as 4 nm. Raman and X-ray photoelectron spectroscopy on BN films show no significant oxidation caused by PE-ALD of Al 2 O 3 . Inserting the BN layer creates an atomically abrupt interface significantly reducing interface charges between the graphene and Al 2 O 3 as compared to use of a 2 nm Al buffer layer. This results in a much smaller Dirac voltage (− 1 V) and hysteresis (0.9 V) when compared to FETs with the Al layer (V Dirac = − 6.1 V and hysteresis = 2.9 V).

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.

beta-Ga2O3 thin-channel MOSFETs were evaluated using both dc and pulsed ${I}$ - ${V}$ measurements. The reported pulsed ${I}$ - ${V}$ technique was used to study self-heating effects in the MOSFET channel. The device was analyzed over a large temperature range of 23 C-200 C. A relationship between dissipated power and channel temperature was established, and it was found that the MOSFET channel was heating up to 208 C when dissipating 2.5 W/mm of power. The thermal resistance of the channel was found to be 73 C-mm/W. The results are supported with the experimental Raman nanothermography and thermal simulations and are in reasonable agreement with pulsed ${I}$ - ${V}$ findings. The high thermal resistance underpins the importance of optimizing thermal management in future Ga2O3 devices.

The power switching potential of Ga 2 O 3 has been well established in the last several years due to the material's high critical electric field $(\mathrm{E}_{\mathrm{C}})$ strength. This allows for dramatic device scaling and operation at high voltage with reduced series resistance in power switching applications. The same argument applies for RF power amplification, where the high $\mathrm{E}_{\mathrm{C}}$ of Ga 2 O 3 allows FETs to be scaled to smaller dimensions while operating at higher operating voltages than existing RF FETs. At the same time, ab initio calculations published in 2017 for velocity-field characteristics of Ga 2 O 3 indicate a peak electron velocity of $2\mathrm{x}10^{7}$ cm/s which suggests the power-frequency product for Ga 2 O 3 is significantly greater than that of GaN. In 2017, the first demonstrated CW RF operation for Ga 2 O 3 FETs was in part limited by the thermal resistance and immaturity of heat extraction techniques to ~300 mW/mm. Since then, pulsed RF power measurement techniques have been implemented to accelerate electrical characterization of RF Ga 2 O 3 FETs. Pulsed RF output power $> 500$ mW/mm has been measured at 1 GHz. Advances in laterally scaled devices and topology design to ensure electrons achieve saturated velocity in the channel will be discussed.

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.

Carrier concentration control by impurity dopants in epitaxial Ga2O3 thin films is progressing to deliver high mobility films for device structures. Si-doped Ga2O3 thin films were fabricated by pulsed laser deposition on (010) β-Ga2O3 substrates from Ga2O3 targets with 0.01–1 wt. % SiO2 yielding films with an electron mobility range consistent with other vapor growth techniques. Single crystal, homoepitaxial growth as determined by high resolution transmission electron microscopy and x-ray diffraction was observed, with a high Si dopant level causing film tensile strain as indicated by both techniques. The influence of oxygen on conductivity using different O2 pressures during deposition and O2/Ar mixtures with a fixed working pressure of 1.33 Pa was determined. With this optimized deposition pressure and atmosphere condition, a carrier concentration and mobility range of 3.25 × 1019 cm−3–1.75 × 1020 cm−3 and 20 cm2/V s–27 cm2/V s was achieved in films from Ga2O3-0.025 wt. % SiO2 and Ga2O3-1 wt. % SiO2 targets, respectively. A highest conductivity of 798 S cm−1 was achieved in films deposited at 550 °C–590 °C with targets of 0.05–1 wt. % SiO2. The electrically active and chemical Si content in films deposited at 550 °C was found to exceed the expected Si ablation target composition in all cases except the highest 1 wt. % SiO2 target attributed to imprecise target manufacturer compositional control at low SiO2 doping levels. Diminished electrical and structural quality films resulted from all targets at a 450 °C deposition temperature.

In this work, we provide early insight into the combined tradespace for both power switching and RF applications afforded by the high critical, electric-field strength of β-Ga 2 O 3 . MOSFETs formed by homoepitaxial growth of β-Ga 2 O 3 films doped with Sn, Si, and Ge on bulk substrates have been characterized electrically. Several key milestones have been achieved such as enhancement-mode operation > 600 V, low ohmic contact resistance <; 0.2 Ω·mm, and RF power gain in the GHz regime. These results show great promise for monolithic and hybrid integration of RF amplifiers and switch technologies.

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.