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In the present study, p-GaN/AlGaN/GaN HEMTs treated with hydrogen plasma passivation were fabricated. Capacitance–voltage (C-V) and current–voltage(I-V) characteristics of these devices were subsequently measured. The relationship between polarization Coulomb field (PCF) scattering and the subthreshold swing(SS) for E-mode p-GaN/AlGaN/GaN was investigated. The two-dimensional electron gas (2DEG) concentration beneath the gate-source (G-S) and gate-drain (G-D) regions of the p-GaN HEMT was calculated at zero gate bias voltage using TCAD software. By integrating measured I-V and C-V data, the 2DEG concentration was determined for various gate bias voltages, facilitating iterative calculations to derive additional parameters such as polarization charge and electron mobility. The calculation results show that for the E-mode GaN HEMT, the PCF was gradually weakened as the additional polarization charge decreased with the increase in V GS . Moreover, for the devices with stronger PCF scattering, the value of the SS was smaller, and the SS value was reduced by over 60%.

In this letter, a novel approach is presented to overcome issues in AlGaN/GaN high electron mobility transistors (HEMTs), such as metal discontinuity of the gate stemmed from conventional mesa isolation. This usually requires a careful mesa etch process to procure an anisotropic mesa-wall profile. An alternative technique is the use of ion implantation for device isolation instead of conventional mesa for a planar device formation. However, ion implantation is a costly process and not always easily accessible. In this work, the proposed method is to simply extend the mesa below the gate just enough to accommodate the gatefeed, thereby ensuring the entire gate is planar in structure up to the gatefeed. The newly developed device exhibited no compromise to the DC (direct current) and RF (radio frequency) performance. Conversely, it produced a planar gate configuration with an enhanced DC transconductance (approximately 20% increase is observed) and a lower gate leakage while the etch process is considerably simplified. Similarly, the RF transconductance of proposed device (device B) increased by 80% leading to considerable improvements in RF performance.

Thermoelectric conversion is an energy harvesting technology that directly converts waste heat from various sources into electricity by the Seebeck effect of thermoelectric materials with a large thermopower (S), high electrical conductivity (σ), and low thermal conductivity (κ). State‐of‐the‐art nanostructuring techniques that significantly reduce κ have realized high‐performance thermoelectric materials with a figure of merit (ZT = S2∙σ∙T∙κ−1) between 1.5 and 2. Although the power factor (PF = S2∙σ) must also be enhanced to further improve ZT, the maximum PF remains near 1.5–4 mW m−1 K−2 due to the well‐known trade‐off relationship between S and σ. At a maximized PF, σ is much lower than the ideal value since impurity doping suppresses the carrier mobility. A metal‐oxide‐semiconductor high electron mobility transistor (MOS‐HEMT) structure on an AlGaN/GaN heterostructure is prepared. Applying a gate electric field to the MOS‐HEMT simultaneously modulates S and σ of the high‐mobility electron gas from −490 µV K−1 and ≈10−1 S cm−1 to −90 µV K−1 and ≈104 S cm−1, while maintaining a high carrier mobility (≈1500 cm2 V−1 s−1). The maximized PF of the high‐mobility electron gas is ≈9 mW m−1 K−2, which is a two‐ to sixfold increase compared to state‐of‐the‐art practical thermoelectric materials. High‐mobility 2D electron gas induced at an AlGaN/GaN heterointerface exhibits a high thermoelectric power factor of ≈9 mW m−1 K−2 at room temperature, which is an order magnitude greater than that of doped GaN bulk and a factor of 2–6 compared to those of state‐of‐the‐art practical thermoelectric materials (1.5–4 mW m−1 K−2).

In this work, temperature-dependent transient threshold voltage (VT) instability behaviors in p-GaN/AlGaN/GaN HEMTs, with both Schottky gate (SG) and Ohmic gate (OG), were investigated systematically, under negative gate bias stress, by a fast voltage sweeping method. For SG devices, a concave-shaped VT evolution gradually occurs with the increase in temperature, and the concave peak appears faster with increasing reverse bias stress, followed by a corresponding convex-shaped VT recovery process. In contrast, the concave-shaped VT evolution for OG devices that occurred at room temperature gradually disappears in the opposite shifting direction with the increasing temperature, but the corresponding convex-shaped VT recovery process is not observed, substituted, instead, with a quick and monotonic recovery process to the initial state. To explain these interesting and different phenomena, we proposed physical mechanisms of time and temperature-dependent hole trapping, releasing, and transport, in terms of the discrepancies in barrier height and space charge region, at the metal/p-GaN junction between SG and OG HEMTs.

This work proposes new architecture, supported by analytical modelling and computer-aided design (CAD) simulations, for a highly sensitive monolayer graphene-gated AlGaN/GaN HEMT terahertz (THz) detector operating at room temperature (RT). The monolayer graphene gate acts as a surface plasmon absorber for the incident THz radiation. The carrier density perturbation caused by incident THz energy on the monolayer graphene surface is then capacitively coupled to the two-dimensional electron gas (2DEG) channel of the HEMT structure underneath. The channel is partially depleted for increased mobility and nonlinearity with potential asymmetry across the channel for consistent photogeneration. The Drude absorption of THz radiation initiates intraband transitions in monolayer graphene, thereby reducing phonon losses. These reduced phonon losses enable RT THz detection. Based on our simulations, the proposed detector architecture can generate a responsivity of 2.12 × 106 V/W at 1 THz with a broadband bandwidth of 2 THz.

AlGaN/GaN HEMTs were fabricated using two special gate metals, Hf and W, as gate Schottky contact materials. Based on the measured I-V data and two-dimensional scattering theory, the electron mobility corresponding to polarization Coulomb field (PCF) scattering and other scattering mechanisms was calculated. The additional polarization charge (APC) due to the inverse piezoelectric effect (IPE) was also calculated. The differences in the effects of two special gate metals, Hf and W, on the PCF scattering intensity are analyzed from the aspects of Young’s modulus and work function of the metal. It was found that compared with W metal, Hf metal has a smaller Young’s modulus and weaker ability to resist elastic deformation, which makes the AlGaN barrier layer in contact with Hf more easily deformed due to IPE, resulting in more APC under the Hf metal Schottky contact. On the other hand, Hf has a smaller work function compared to W metal, so the 2DEG density is higher. The influence of special gate metals Hf and W on the PCF scattering intensity is the result of the combined effect of these two factors. This study is of great significance for understanding the electron transport mechanisms of AlGaN/GaN HEMTs with special gate metals such as Hf and W, and for further improving the electrical performance and stability of the devices.

Slight changes in potassium levels can affect health. Therefore, rapid, reliable, and quantitative determination of potassium ion content is important for medical diagnosis. AlGaN, as a semiconductor material with good biocompatibility, has many advantages in the development of new potassium ion sensors. Understanding the adsorption behavior of a specific ion on the AlGaN surface and the eventual effect on AlGaN/GaN’s heterostructure interface is the key to obtaining high-performance nitride sensors. In this paper, we calculated the changes in the density of states and energy bands of the material after AlGaN adsorbed potassium ions through first-principles simulation. Combined with two-dimensional device simulation software, the changes in device performance caused by the changes in material properties are presented. The simulation results show that the adsorption of a single potassium ion can cause a current change in the order of milliamperes, providing a theoretical reference for the subsequent development of high-sensitivity potassium ion sensors.

To optimize the thermal design of AlGaN-GaN high-electron-mobility transistors (HEMTs), which incorporate high power densities, an accurate prediction of the underlying thermal transport mechanisms is crucial. Here, a HEMT-structure (Al0.17Ga0.83N, GaN, Al0.32Ga0.68N and AlN on a Si substrate) was investigated using a time-domain thermoreflectance (TDTR) setup. The different scattering contributions were investigated in the framework of phonon transport models (Callaway, Holland and Born-von-Karman). The thermal conductivities of all layers were found to decrease with a temperature between 300 K and 773 K, due to Umklapp scattering. The measurement showed that the AlN and GaN thermal conductivities were a magnitude higher than the thermal conductivity of Al0.32Ga0.68N and Al0.17Ga0.83N due to defect scattering. The layer thicknesses of the HEMT structure are in the length scale of the phonon mean free path, causing a reduction of their intrinsic thermal conductivity. The size-effect of the cross-plane thermal conductivity was investigated, which showed that the phonon transport model is a critical factor. At 300 K, we obtained a thermal conductivity of (130 ± 38) Wm−1K−1 for the (167 ± 7) nm thick AlN, (220 ± 38) Wm−1K−1 for the (1065 ± 7) nm thick GaN, (11.2 ± 0.7) Wm−1K−1 for the (423 ± 5) nm thick Al0.32Ga0.68N, and (9.7 ± 0.6) Wm−1K−1 for the (65 ± 5) nm thick Al0.17Ga0.83N. Respectively, these conductivity values were found to be 24%, 90%, 28% and 16% of the bulk values, using the Born-von-Karman model together with the Hua–Minnich suppression function approach. The thermal interface conductance as extracted from the TDTR measurements was compared to results given by the diffuse mismatch model and the phonon radiation limit, suggesting contributions from inelastic phonon-scattering processes at the interface. The knowledge of the individual thermal transport mechanisms is essential for understanding the thermal characteristics of the HEMT, and it is useful for improving the thermal management of HEMTs and their reliability.

A 2-D simulation of off-state breakdown voltage (VBD) for AlGaN/GaN high electron mobility transistors (HEMTs) with multi field-plates (FPs) is presented in this paper. The effect of geometrical variables of FP and insulator layer on electric field distribution and VBD are investigated systematically. The FPs can modulate the potential lines and distribution of an electric field, and the insulator layer would influence the modulation effect of FPs. In addition, we designed a structure of HEMT which simultaneously contains gate FP, source FP and drain FP. It is found that the VBD of AlGaN/GaN HEMTs can be improved greatly with the corporation of gate FP, source FP and drain FP. We achieved the highest VBD in the HEMT contained with three FPs by optimizing the structural parameters including length of FPs, thickness of FPs, and insulator layer. For HEMT with three FPs, FP-S alleviates the concentration of the electric field more effectively. When the length of the source FP is 24 μm and the insulator thickness between the FP-S and the AlGaN surface is 1950 nm, corresponding to the average electric field of about 3 MV/cm at the channel, VBD reaches 2200 V. More importantly, the 2D simulation model is based on a real HMET device and will provide guidance for the design of a practical device.

Due to the enhanced-mode (E-mode) operation, AlGaN/GaN high-electron-mobility transistors (HEMTs) are considered to be safer for circuit operation. In order to improve the threshold voltage (Vth) of the device, this work provides a hybrid gate structure HEMT by embedding a P-GaN cap on the etched graded AlGaN barrier layer. Through simulation calculations, the P-GaN cap (thickness of P-GaN = 50 nm, concentration of P-type = 2 × 1018 cm−3) and the aluminum (Al) composition (Al:0.3 → 0.24), in the graded AlGaN barrier layer were optimized. Although simulation calculations show that the optimized P-GaN layer can significantly increase the device’s Vth to 8.6 V and transconductance (gm) to 94.7 mS/mm, the device exhibits a lower saturation current (Isat). Therefore, to improve the output characteristics of the devices, the addition of an N-well in the GaN channel layer of such structures was proposed. It can increase the device’s source–drain current while maintaining a steady Vth. Compared with the HEMT structure/combined P-GaN cap with recessed gate and a graded AlGaN barrier layer, the device with the added N-well exhibits a significant improvement of 11.2% in the saturation current (Isat = 718 mA/mm). The results demonstrate that HEMT structures combining recessed gates and P-GaN with N-well have promising applications in next-generation high-power devices.