A scattering matrix technique is used to study the transmission probability through a flat semiconductor / vacuum interface considering the effective mass difference between the two materials. A comparison is made between the longitudinal and transverse energy dependence of the transmission probability calculated using the BenDaniel-Duke (BD) and ZhuKroemer (ZK) boundary conditions at the semiconductor / vacuum interface. For longitudinal energy between the minimum of the conduction band and a few kappa T-B above the Fermi level in the semiconductor, the transmission probability can be an order of magnitude smaller when using the ZhuKroemer boundary conditions compared to the BenDanielDuke boundary conditions. The Zhu-Kroemer boundary conditions should be used to calculate the field emission current through a semiconductor/vacuum interface.

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

We report the design, fabrication, and measurement of the field emission (FE) characteristics of AlGaN/GaN nanoscale lateral vacuum diodes with triangular cathodes and cathode to anode spacings from 50 to 600 nm. The FE characteristics of the AlGaN/GaN diodes with metallic or AlGaN/GaN anodes show successful rectification with forward bias FE current in the range of microamperes or milliamperes, respectively, when biased within a maximum range varying from 10 to 30 V. In the forward bias mode, the measured current Im vs applied anode to cathode bias Vm are well fitted to Murphy–Good profiles associated with FE at higher biases, and an Ohmic leakage profile below the threshold for FE. Our results are the first successful demonstration of FE of electrons between the two two-dimensional electron gases (2DEGs) present on both sides of a nanogap formed by electron lithography through an AlGaN/GaN heterojunction. A qualitative explanation of the loop-type FE characteristics of both AlGaN/GaN vacuum diodes, with either metallic or AlGaN/GaN anodes, is presented.

- Using numerical modeling it is shown that performance of Littrow retroreflectors can be enhanced at both polarizations of incident light due to resonantly enhanced plasmonic light scattering in slot arrays formed by Au, Ag, AI, and Cu metallic stripes with 20–40 nm thicknesses.

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).

A scattering matrix technique is used to calculate the longitudinal and transverse energy dependence of the transmission probability through various heterostructures using both the BenDaniel-Duke (BD) and the lesser known Zhu-Kroemer (ZK) boundary conditions to take into account the spatial dependence of the effective mass. We first illustrate the large difference in the transmission probabilities calculated using both boundary conditions for the simple problems of tunneling through a potential step, a single rectangular barrier, and a resonant tunneling device. Then, we present numerical calculations of the external electric field dependence of the field emission (FE) current from a n-doped GaAs semiconductor/vacuum interface using both boundary conditions, showing that the BD boundary conditions underestimate the FE current for large values of the applied external electrostatic field. A comparison of calculated FE characteristics with FE data may be a way to determine the appropriate boundary conditions to solve tunneling problems through heterostructures with spatially varying effective mass.

We investigate the temperature dependence of field emission (FE) characteristics of AlGaN/GaN heterojunction-based lateral nanoscale vacuum diodes over a temperature range varying from 77 to 373 kelvin. The vacuum diodes have a sharp (trochoidal-like) cathode and blunted anode with the shortest distance between the tip of the cathode and the anode of 210 nanometers. The DC FE characteristics were recorded using a compliance current of 100 nanoamperes. Under forward mode of operation, the vacuum diodes exhibit three regimes of operation: one associated with FE from adsorbates on the tip of the cathode at low applied bias, followed by FE from the bare cathode at larger forward bias, and finally onset of self-heating effects. The latter leads to a smaller FE current under reverse sweep. In the reverse sweep, the current-voltage characteristics suggest the onset of conduction through the substrate.

It is shown that Littrow retroreflectors show an interplay of the grating properties (“structure factor”) and plasmonic resonant properties (“form factor”) which leads to highly efficient simultaneous retroreflector performance in both polarizations of visible light.

This paper reports a temperature-dependent ASM-HEMT for modeling GaN HEMTs at elevated temperatures. Modifications to the standard ASM-HEMT were developed to accurately capture the DC and RF measurements collected at varying chuck temperatures. Several results are reported which validate the model including DC-IV, pulsed-IV, scattering-parameter, and load-pull measurements. The model is then used to extrapolate the performance of the GaN HEMT to twice the operating temperature at which the model was validated. This work could be useful for understanding and modeling GaN HEMTs in high-temperature environment applications.

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.

Waveguide gratings with structured period provide controllable ratio between coupling coefficients in different diffraction orders and allow for control of resonant reflection spectra. We report conceptual model, numerical studies, and fabrication of GaN structured period waveguide gratings designed for the mid-IR spectral range.

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.

Field emission (FE) characteristics of 2-terminal Au lateral nanoscale vacuum field emission devices with different dielectric substrates is reported in this work. Field orthodoxy is tested with the Murphy Good plot. Poole-Frenkel leakage is presented as a primary mechanism for emission at low voltages through the substrates with some reported burn-in effects removed with correct substrate choice. The results are significant in that the leakage effects can be difficult to discern from pure PE and are thus important to consider in future designs of these types of devices.

This article presents for the first time a direct connection between gate lag observed in drain current transient measurements of gallium nitride (GaN) high-electron-mobility transistors (HEMTs) and traps located in the barrier of the transistor epitaxy. Semiclassical numerical simulations are presented using the Air Force Research Laboratory’s (AFRL’s) Fermi kinetics transport (FKT) solver and are validated with drain current transient measurements. Capacitance–voltage ( ${C} - {V}$ ) and conductance–voltage ( ${G} - {V}$ ) measurements are also presented to provide further insights into the trap location used in the FKT simulations. These simulations indicate that equivalent defects located specifically at the AlGaN barrier/GaN cap interface of an AFRL GaN HEMT with a density of $7.5\times 10^{{12}}$ cm−2 and positioned 1.464 eV below the GaN cap conduction band edge were the salient traps linked to the gate-lag phenomenon. The study highlights the importance of experimentally benchmarked device simulation for trapping analysis in GaN HEMTs and may provide significant insights into device engineers for mitigating trapping effects in state-of-the-art GaN technologies.

We successfully demonstrate for the first-time field emission (FE) from and to the two-dimensional electron gas (2DEG) formed in AlGaN/GaN heterojunction based lateral nanoscale vacuum emission diodes. In addition, we demonstrate FE with an AlGaN/GaN cathode and metallic anode. Our FE measurements demonstrate that these vacuum diodes with AlGaN/GaN and metallic anodes can deliver emission current in the range of microamps to milliamps, respectively, when biased within a range from 5 to 30 V.

We successfully demonstrate for the first-time field emission (FE) from and to the two-dimensional electron gas (2DEG) formed in AlGaN/GaN heterojunction based lateral nanoscale vacuum emission diodes. In addition, we demonstrate FE with an AlGaN/GaN cathode and metallic anode. Our FE measurements demonstrate that these vacuum diodes with AlGaN/GaN and metallic anodes can deliver emission current in the range of microamps to milliamps, respectively, when biased within a range from 5 to 30 V.

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.

We demonstrate a passivated MESFET fabricated on (010) Si-doped $\beta $ -Ga 2 O 3 with breakdown over 2.4 kV without field plates, high Power Figure of Merit (PFOM), and high estimated Huang’s Material Figure of Merit (HMFOM), owing to low gate charge and high breakdown. MESFETs with 13 $\mu \text{m}$ source-drain spacing and 75 nm channel exhibited a current density of 61 mA/mm, peak transconductance of 27 mS/mm, and on-resistance of ${133}~\Omega \cdot \text {mm}$ . The device showed a PFOM competitive with state-of-the-art $\beta $ -Ga 2 O 3 devices and a record high estimated HMFOM for a $\beta $ -Ga 2 O 3 device, competitive with commercial wide-band gap devices. This demonstrates high-performance $\beta $ -Ga 2 O 3 devices as viable multi-kV high-voltage power switches.