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β‐Ga2O3‐based semiconductor devices are expected to have significantly improved high‐power and high‐temperature performance due to its ultrawide bandgap of close to 5 eV. However, the high‐temperature operation of these ultrawide‐bandgap devices is usually limited by the relatively low 1–2 eV built‐in potential at the Schottky barrier with most high‐work‐function metals. Herein, heterojunction p‐NiO/n‐β‐Ga2O3 diodes fabrication and optimization for high‐temperature device applications are reported, demonstrating a current rectification ratio (ION/IOFF) of more than 106 at 410 °C. The NiO heterojunction diode can achieve higher turn‐on (VON) voltage and lower reverse leakage current compared to the Ni‐based Schottky diode fabricated on the same single‐crystal β‐Ga2O3 substrate, despite charge transport dominated by interfacial recombination. Electrical characterization and device modeling show that these advantages are due to a higher built‐in potential and additional band offset. These results suggest that heterojunction p–n diodes based on β‐Ga2O3 can significantly improve high‐temperature electronic device and sensor performance. [ABSTRACT FROM AUTHOR]

Ultrawide bandgap Al0.7Ga0.3N MESFETs with refractory Tungsten Schottky and Ohmic contacts are studied in 300–675 K environments. Variable-temperature dc electrical transport reveals large ON-state drain current densities for an AlGaN device: 209 mA/mm at 300 K and 156 mA/mm at 675 K in the ON-state (25% reduction). Drain and gate currents are only weakly temperature-dependent, suggesting potential for engineering temperature invariant operation. The ON-/ OFF-ratio is limited by OFF-state leakage through the gate, which is attributed to damage from sputter deposition. Future work using refractory metals with larger work functions that are deposited by electron beam deposition is proposed. [ABSTRACT FROM AUTHOR]

We introduce a deep-recessed gate architecture in β-Ga2O3 delta-doped field-effect transistors (FETs) for improvement in dispersion and breakdown properties. The device design incorporates an unintentionally doped (UID) β-Ga2O3 layer as the passivation dielectric. To fabricate the device, the deep-recess geometry was developed using BCl3 plasma-based etching at ~5 W reactive ion etching (RIE) power to ensure minimal plasma damage. Etch damage incurred with plasma etching was mitigated by annealing in vacuum at temperatures above 600 °C. A gate-connected field-plate edge termination was implemented for efficient field management. Negligible surface dispersion with lower knee walkout at high VDS, and better breakdown characteristics compared to their unpassivated counterparts were achieved. A three-terminal OFF-state breakdown voltage of 315 V, corresponding to an average breakdown field of 2.3 MV/cm was measured. The device breakdown was limited by the field-plate/passivation edge and presents scope for further improvement. This demonstration of epitaxially passivated FET is a significant step for β-Ga2O3 technology since the structure simultaneously provides control of surface-related dispersion and excellent field management. [ABSTRACT FROM AUTHOR]

We demonstrate DC-RF dispersion-free graded AlGaN channel transistor with an epitaxial passivation. The device used for this experiment was an AlGaN channel polarization-graded field effect transistor (PolFET) with Al-composition grading from 0% to 30%. We were able to reduce the dispersion to almost zero current collapse and zero knee-walkout for pulsed I–V up to 30 V drain quiescent bias condition with epitaxial passivation, compared to 8 V knee-walkout and 25% current collapse for PolFETs with traditional PECVD SiNx for the same measure conditions. We also report large signal power density and two-tone linearity for these devices up to X-band frequencies. [ABSTRACT FROM AUTHOR]

In this Letter, we demonstrate a Pt/BaTiO3/Al0.58Ga0.42N lateral heterojunction diode with enhanced breakdown characteristics. By using BaTiO3, a high-k material, as a dielectric material between the anode and semiconductor, the peak electric field at the anode edge near the cathode was significantly reduced and an average breakdown field exceeding 8 MV/cm was achieved for devices with an anode to cathode spacing of <0.2 μm. In contrast, Pt/Al0.58Ga0.42N control Schottky diodes displayed an average breakdown field of ∼4 MV/cm for devices with similar dimensions. The use of a high-k dielectric can more effectively utilize the high breakdown fields in ultra-wide bandgap materials by proper management of the electric field. This demonstration thus provides a framework to realize ultra-scaled lateral devices with improved breakdown characteristics. [ABSTRACT FROM AUTHOR]

In this letter, we discuss the application of low pressure chemical vapor deposition (LPCVD) grown SiNx passivation-first process to improve the power density and linearity performance of a metal oxide chemical vapor deposition (MOCVD) grown AlGaN channel polarization-graded field-effect transistor (PolFET). Significantly improved dispersion behavior was observed compared to plasma enhanced chemical vapor deposition (PECVD) grown SiNx passivation. The Current collapse at 30 V drain quiescent condition for pulsed I-V was reduced to 8% (LPCVD) from 25% (PECVD). 10 GHz load-pull measurement showed a maximum output power density of 3.4 W/mm with a peak power added efficiency (PAE) of 40%. Two-tone intermodulation distortion measurement at 10 GHz for devices with $150\boldsymbol {\mu }\text{m}$ width revealed an OIP3 of 39 dBm and an excellent corresponding linearity figure of merit OIP3/ $\text{P}_{{\textit {DC}}}$ of 13.3 dB. This is the best device level OIP3/ $\text{P}_{{\textit {DC}}}$ reported to date at X-band for III-Nitride microwave transistors. [ABSTRACT FROM AUTHOR]

In this letter, we design and demonstrate an improved metalorganic chemical vapor deposition (MOCVD) grown reverse Al-composition graded contact layer, whereby the Al-composition of AlxGa1−xN in the contact layer is graded from the higher Al-composition as in the channel to lower Al-composition, to achieve a low resistance contact to MOCVD grown ultrawide bandgap Al0.70Ga0.30N channel metal-semiconductor field-effect transistors. Increasing the thickness of the reverse graded layer was found to improve contact layer resistance significantly, leading to a contact resistivity of 3.3 × 10−5 Ω cm2. Devices with a gate length, LG, of 0.6 μm and a source-drain spacing, LSD, of 1.5 μm displayed a maximum current density, IDS,MAX, of 635 mA/mm with an applied gate voltage, VGS, of +2 V. Breakdown measurements on transistors with a gate to drain spacing, LGD, of 770 nm had breakdown voltage greater than 220 V, corresponding to a minimum breakdown field of 2.86 MV/cm—almost 3× higher than that exhibited by lateral GaN channel devices with similar dimensions. This work provides a framework for the design of low resistance contacts to MOCVD grown high Al-content AlxGa1−xN channel transistors. [ABSTRACT FROM AUTHOR]

As an ultra-wide bandgap semiconductor, $\beta $ -Ga2O3 has attracted great attention for high-power, high-voltage, and optoelectronic applications. However, until now, high-frequency performance of gallium oxide devices has been limited to relatively low current gain cutoff frequencies below 5 GHz. Here, we show that highly localized delta-doping designs can enable high-sheet-charge density to enable devices with short gate lengths that allow high-frequency operation. Field-effect transistors with a gate length of 120 nm on such delta-doped $\beta $ -Ga2O3 are reported here with extrinsic unity current gain frequency of 27 GHz. The device has a peak drain current of 260 mA/mm, transconductance (gm) of 44 mS/mm, and three-terminal off-state breakdown voltage of 150 V. These results demonstrate that the potential of $\beta $ -Ga2O3 for future RF and millimeter-wave device applications. [ABSTRACT FROM AUTHOR]

We report on the power and linearity performance of metal–organic chemical vapor deposition grown polarization-engineered novel structure that combines the AlGaN/GaN high-electron-mobility transistor with a graded InGaN sub-channel layer. The fabricated transistors with composite two-dimensional (2D) and three-dimensional (3D) electron channels showed nearly flat transconductance and power gain profiles. The maximum ${f}_{T}$ and ${f}_{ {max}}$ values of 18 GHz and 38 GHz were measured for 0.7- ${\mu }\text{m}$ gate-length transistors. Load-pull measurement at 10 GHz revealed a maximum output power of 2.2 W/mm. Two-tone measurement at 10 GHz showed an excellent OIP3 of 38 dBm for 150- ${\mu }\text{m}$ device width and a corresponding linearity figure of merit OIP3/ $\text{P}_{\textsf {DC}}$ of 9.7 dB. These results suggest that InGaN-based composite 2D–3D channel transistors could be useful for high-frequency applications requiring high linearity. [ABSTRACT FROM AUTHOR]

We report on the power and linearity performance of metal organic chemical vapor deposition grown AlGaN channel polarization-graded field-effect transistor (PolFET). The fabricated transistors with 3-D electron channels showed nearly flat transconductance profiles. Maximum ${f}_{T}$ and ${f}_{\text {max}}$ of 23 and 65 GHz were measured for 0.7- $\mu \text{m}$ gate-length transistors, corresponding to an ${f}_{T}$ - ${L}_{G}$ product of 16.2 GHz $\cdot \mu \text{m}$. Load-pull measurement at 10 GHz revealed a maximum output power of 2 W/mm with a maximum small signal gain of 16 dB. Two-tone measurement at 10 GHz showed an OIP3 of 33 dBm for 150- $\mu \text{m}$ device width and a corresponding linearity figure-of-merit OIP3/ $\text{P}_{\text {DC}}$ of 3.4 dB. These results suggest that PolFETs could be useful for high-frequency applications requiring high linearity. [ABSTRACT FROM AUTHOR]

We report on ultra-wide bandgap (UWBG) Al0.7Ga0.3N channel metal–oxide–semiconductor field-effect transistors (MOSFETs) grown by metal-organic chemical vapor deposition. Employing reverse Al composition graded ohmic contact layers and 20 nm Al2O3 gate-dielectric, 250 nm thick Al0.7Ga0.3N:Si channel MOSFETs resulted in the maximum current density of 0.5 A/mm, which is the highest value reported for AlGaN channels with Al composition >0.25. Transistors with a gate-drain spacing ( L\mathrm{ GD}) of 1.7~\mu \textm demonstrated a breakdown voltage ( V\mathrm{ DG}) of ~620 V, translating in an average lateral breakdown field of ~3.6 MV/cm. This work establishes UWBG AlGaN as a promising candidate for advanced RF applications. [ABSTRACT FROM PUBLISHER]