Search Results (424)

Devices under semi-on-state stress often suffer from more severe current collapse than when they are in the off-state, which causes an increase in dynamic on-resistance. Therefore, characterization of the trap states is necessary. In this study, temperature-dependent transient recovery current analysis determined a trap energy level of 0.08 eV under semi-on-state stress, implying that interface traps are responsible for current collapse. Multi-frequency capacitance–voltage (C-V) testing was performed on the MIS diode, calculating that interface trap density is in the range of $1.37\times {10}^{13}$ to $6.07\times {10}^{12}$${\mathrm{cm}}^{-2}$${\mathrm{eV}}^{-1}$ from $E_C-E_T=0.29$ eV to 0.45 eV. Full article

In this paper, a novel AlGaN/GaN HEMT structure with a P-GaN buried layer in the buffer layer and a locally doped barrier layer under the gate (PN-HEMT) is proposed to enhance its resistance to single event transient (SET) effects while also overcoming the degradation of other characteristics. The device operation mechanism and characteristics are investigated by TCAD simulation. The results show that the peak electric field and impact ionization at the gate edges are reduced in the PN-HEMT due to the introduced P-GaN buried layer in the buffer layer. This leads to a decrease in the peak drain current (I_peak) induced by the SET effect and an improvement in the breakdown voltage (BV). Additionally, the locally doped barrier layer provides extra electrons to the channel, resulting in higher saturated drain current (I_D,sat) and maximum transconductance (g_max). The I_peak of the PN-HEMT (1.37 A/mm) is 71.8% lower than that of the conventional AlGaN/GaN HEMT (C-HEMT) (4.85 A/mm) at 0.6 pC/µm. Simultaneously, I_D,sat and BV are increased by 21.2% and 63.9%, respectively. Therefore, the PN-HEMT enhances the hardened SET effect of the device without sacrificing other key characteristics of the AlGaN/GaN HEMT. Full article

The small-signal S parameters of the fabricated double-finger gate AlGaN/GaN high electron mobility transistors (HEMTs) were measured at various direct current quiescent operating points (DCQOPs). Under active bias conditions, small-signal equivalent circuit (SSEC) parameters such as R_s and R_d, and intrinsic parameters were extracted. Utilizing f_T and the SSEC parameters, the effective electron velocity (${\nu }_{e-eff}$) and intrinsic electron velocity (${\nu }_{e-\mathrm{int}}$) corresponding to each gate bias (V_GS) were obtained. Under active bias conditions, the influence mechanism of V_GS on ${\nu }_{e-eff}$ was systematically studied, and an expression was established that correlates ${\nu }_{e-eff}$, ${\nu }_{e-\mathrm{int}}$, and bias-dependent parasitic resistances. Through the analysis of the main scattering mechanisms in AlGaN/GaN HEMTs, it has been discovered that the impact of V_GS on ${\nu }_{e-eff}$ should be comprehensively analyzed from the aspects of ${\nu }_{e-\mathrm{int}}$ and parasitic resistances. On the one hand, changes in V_GS influence the intensity of polar optical phonon (POP) scattering and polarization Coulomb field (PCF) scattering, which lead to changes in ${\nu }_{e-\mathrm{int}}$ dependent on V_GS. The trend of ${\nu }_{e-\mathrm{int}}$ with changes in V_GS plays a dominant role in determining the trend of ${\nu }_{e-eff}$ with changes in V_GS. On the other hand, both POP scattering and PCF scattering affect ${\nu }_{e-eff}$ through their impact on parasitic resistance. Since there is a difference in the additional scattering potential corresponding to the additional polarization charges (APC) between the gate-source/drain regions and the region under the gate, the mutual effects of PCF scattering on the under-gate electron system and the gate-source/drain electron system should be considered when adjusting the PCF scattering intensity through device structure optimization to improve linearity. This study contributes to a new understanding of the electron transport mechanisms in AlGaN/GaN HEMTs and provides a novel theoretical basis for improving device performance. Full article

In this work, the DC performance and RF characteristics of GaN-based high-electron-mobility transistors (HEMTs) using the SiN_x stress-engineered technique were systematically investigated. It was observed that a significant reduction in the peak electric field and an increase in the effective barrier thickness in the devices with compressive SiN_x passivation contributed to the suppression of Fowler–Nordheim (FN) tunneling. As a result, the gate leakage decreased by more than an order of magnitude, and the breakdown voltage (BV) increased from 44 V to 84 V. Moreover, benefiting from enhanced gate control capability, the devices with compressive stress SiN_x passivation showed improved peak transconductance from 315 mS/mm to 366 mS/mm, along with a higher cutoff frequency (f_t) and maximum oscillation frequency (f_max) of 21.15 GHz and 35.66 GHz, respectively. Due to its enhanced frequency performance and improved pinch-off characteristics, the power performance of the devices with compressive stress SiN_x passivation was markedly superior to that of the devices with stress-free SiN_x passivation. These results confirm the substantial potential of the SiN_x stress-engineered technique for high-frequency and high-output power applications, which are crucial for future communication systems. Full article

This study investigates the operational characteristics of AlGaN/GaN high-electron-mobility transistors (HEMTs) by employing various passivation materials with different dielectric constants and passivation structures. To ensure the simulation reliability, the parameters were calibrated based on the measured data from the fabricated basic Si₃N₄ passivation structure of the HEMT. The Si₃N₄ passivation material was replaced with high-k materials, such as Al₂O₃ and HfO₂, to improve the breakdown voltage. The Al₂O₃ and HfO₂ passivation structures achieved breakdown voltage improvements of 6.62% and 17.45%, respectively, compared to the basic Si₃N₄ passivation structure. However, the increased parasitic capacitances reduced the cut-off frequency. To mitigate this reduction, the operational characteristics of hybrid and partial passivation structures were analyzed. Compared with the HfO₂ passivation structure, the HfO₂ partial passivation structure exhibited a 7.6% reduction in breakdown voltage but a substantial 82.76% increase in cut-off frequency. In addition, the HfO₂ partial passivation structure exhibited the highest Johnson’s figure of merit. Consequently, considering the trade-off relationship between breakdown voltage and frequency characteristics, the HfO₂ partial passivation structure emerged as a promising candidate for high-power and high-frequency AlGaN/GaN HEMT applications. Full article

This paper will evaluate the surge current robustness of different devices in relation to the active short circuit (ASC). For the purposes of this study, a Si IGBT and its diode, two SiC MOSFETs with different voltage ratings, a SiC JFET, and three GaN HEMTs will be compared. For the GaN devices, a eMode, a dMode, and a cascode device are employed. With the exception of the Si diode, all devices exhibited a current saturation effect. This saturation will result in significant losses and, ultimately, a thermal defect. For all devices, a safe operating area (SOA) criterion is established. For the SiC and GaN devices, the saturation voltage can be employed to define the safe operating area (SOA) criterion. In this context, two on-state resistance models will be defined for these devices. One is solely temperature-dependent, while the other also considers current saturation. Consequently, the saturation voltage and the on-resistance model represent a straightforward methodology for evaluating the ASC robustness of the devices. For all devices, a recommendation for a loss model and SOA criterion will be provided. Finally, the surge current robustness of all devices is compared. The Si, SiC and GaN devices exhibit comparable high surge current robustness in the application, with the exception of the GaN eMode, which is susceptible to strong current saturation. Full article

We have investigated the electrical properties and reliability of AlGaN/GaN high electron mobility transistors (HEMT) under high-temperature RF overdrive stress. The experimental results show that the drain current and transconductance of the device decrease at 25 °C and 55 °C but do not change significantly at 85 °C before and after the stress. The decline rate of the saturation drain current, the degradation amplitude of transconductance, and the drift amplitude of threshold voltage decrease with the increase in temperature. The results of pulse I–V and low-frequency noise tests show that the current collapse is inhibited, and the trap density is reduced at higher temperatures. The Electroluminescence (EL) test shows that the luminescence characteristics of the device after RF overdrive stress are more scattered and weaker. We believe that the degradation at lower temperatures is mainly due to the influence of the hot electron effect (HEE), while the change in electrical properties at higher temperatures is due to the weakening of HEE and the improvement of the Schottky interface. Full article

In this study, metal–silicide-based contacts to GaN-cap/AlGaN/AlN-spacer/GaN-on-Si heterostructure were investigated. Planar Schottky diodes with Cu-covered anodes comprising silicide layers of various metal–silicon (M–Si) compositions were fabricated and characterized in terms of their electrical parameters and thermal stability. The investigated contacts included Ti–Si, Ta–Si, Co–Si, Ni–Si, Pd–Si, Ir–Si, and Pt–Si layers. Reference diodes with pure Cu or Au/Ni anodes were also examined. To test the thermal stability, selected devices were subjected to subsequent annealing steps in vacuum at incremental temperatures up to 900 °C. The Cu/M–Si anodes showed significantly better thermal stability than the single-layer Cu contact, and in most cases exceeded the stability of the reference Au/Ni contact. The work functions of the sputtered thin layers were determined to support the discussion of the formation mechanism of the Schottky barrier. It was concluded that the barrier heights were dependent on the M–Si composition, although they were not dependent on the work function of the layers. An extended, unified Schottky barrier formation model served as the basis for explaining the complex electrical behavior of the devices under investigation. Full article

A comprehensive study of proton irradiation reliability on a bilayer dielectrics SiN_x/Al₂O₃ MIS-HEMT, the common Schottky gate HEMT, and a single dielectric layer MIS-HEMT with SiN_x and with Al₂O₃ for comparison is conducted in this paper. Combining the higher displacement threshold energy of Al₂O₃ with the better surface passivation of the SiN_x layer, the bilayer dielectrics MIS-HEMT presents much smaller degradation of structural materials and of device electrical performance after proton irradiation. Firstly, the least of the defects caused by irradiation suggesting the smallest structural material degradation is observed in the bilayer dielectrics MIS-HEMT through simulations. Then, DC and RF electrical performance of four kinds of devices before and after proton irradiation are studied through simulation and experiments. The smallest threshold voltage degradation rate, the smallest maximum on-current degradation and Gm degradation, the largest cut-off frequency, and the lowest cut-off frequency degradation are found in the bilayer dielectrics MIS-HEMT among four kinds of devices. The degradation results of both structural materials and electrical performance reveal that the bilayer dielectrics MIS-HEMT performs best after irradiation and had better radiation resilience. Full article

In order to solve the performance prediction and design optimization of power amplifiers (PAs), the performance parameters of Gallium Nitride high-electron-mobility transistor (GaN HEMT) PAs at different temperatures are modeled based on the particle swarm optimization–extreme learning machine (PSO-ELM) and extreme learning machine (ELM) in this paper. Then, it can be seen that the prediction accuracy of the PSO-ELM model is superior to that of ELM with a minimum mean square error (MSE) of 0.0006, which indicates the PSO-ELM model has a stronger generalization ability when dealing with the nonlinear relationship between temperature and PA performance. Therefore, this investigation can provide vital theoretical support for the performance optimization of PA design. Full article

The application of GaN HEMTs on silicon substrates in high-voltage environments is significantly limited due to their complex buffer layer structure and the difficulty in controlling wafer warpage. In this work, we successfully fabricated GaN power HEMTs on 6-inch sapphire substrates using a CMOS-compatible process. A 1.5 µm thin GaN buffer layer with excellent uniformity and a 20 nm in situ SiN gate dielectric ensured uniformly distributed V_TH and R_ON across the entire 6-inch wafer. The fabricated devices with an L_GD of 30 µm and W_G of 36 mm exhibited an R_ON of 18.06 Ω·mm and an off-state breakdown voltage of over 3 kV. The electrical mapping visualizes the high uniformity of R_ON and V_TH distributed across the whole 6-inch wafer, which is of great significance in promoting the applications of GaN power HEMTs for medium-voltage power electronics in the future. Full article

This study employs an innovative dynamic switching test system to investigate the dynamic switching characteristics of three p-GaN HEMT devices. The dynamic switching characteristics are different from the previous research on the dynamic resistance characteristics of GaN devices, and the stability of GaN devices can be analyzed from the perspective of switching characteristics. Based on the theory of dynamic changes in threshold opening voltage and capacitance caused by electrical stress, the mechanism of dynamic switching characteristics of GaN HEMT devices is studied and analyzed in detail. The test results have shown that electrical stress induces trap ionization within the device, resulting in fluctuations in electric potential and ultimately leading to alterations in two critical factors of the dynamic switching characteristics of GaN HEMT devices, the parasitic capacitance and the threshold voltage. The dynamic changes in capacitance before and after electrical stress vary among devices, resulting in different dynamic switching characteristics. The test system is capable of extracting the switching waveform for visual comparison and quantitatively calculating the changes in switching parameters before and after electrical stressing. This test provides a prediction for the drift of switch parameters, offering pre-guidance for the robustness of the optimized application scheme. Full article

Developing cost-effective methods to synthesize large-size GaN films remains a challenge owing to the high dislocation density during heteroepitaxy. Herein, AlGaN/GaN HEMTs were grown on 6- and 8-inch Si(111) substrates using metal–organic chemical vapor deposition, and their basic properties and dislocation evolution characteristics were investigated thoroughly. With the insertion of a 100 nm thin AlGaN buffer layer, bow–warp analysis of the epitaxial wafers revealed excellent stress control for both the 6- and 8-inch wafers. HR-XRD and AFM analyses validated the high crystal quality and step-flow growth mode of GaN. Further, Hall measurements demonstrated the superior transport performance of AlGaN/GaN heterostructures. It is worth noting that dislocations tended to annihilate in the AlN nucleation layer, the thin AlGaN buffer layer, and the GaN buffer layer in the initial thickness range of 200–300 nm, which was indicated by ADF-STEM. To be specific, the heterointerfaces exhibited a significant effect on the annihilation of c-type (b = <0001>) dislocations, which led to the formation of dislocation loops. The thin inserted layers within the AlGaN buffer layer played a key role in promoting the annihilation of c-type dislocations, while they exerted less influence on a-type (b = 1/3<11$\overline{2}$0>) and (a+c)-type (b = 1/3<11$\overline{2}$3>) dislocations. Within an initial thickness of 200–300 nm in the GaN buffer layer, a-type and (a+c)-type dislocations underwent strong interactions, leading to considerable dislocation annihilation. In addition, the EELS results suggested that the V-shaped pits in the AlN nucleation layer were filled with the AlGaN thin layer with a low Al content. Full article

To improve the breakdown voltage (BV), a GaN-based high-electron-mobility transistor with a hybrid AlGaN back barrier (HBB-HEMT) was proposed. The hybrid AlGaN back barrier was constructed using the Al₀.₂₅Ga₀.₇₅N region and Al₀.₁G₀.9N region, each with a distinct Al composition. Simulation results of the HBB-HEMT demonstrated a breakdown voltage (1640 V) that was 212% higher than that of the conventional HEMT (Conv-HEMT) and a low on-resistance (0.4 mΩ·cm²). Ultimately, the device achieved a high Baliga’s figure of merit (7.3 GW/cm²) among reported devices of similar size. A back-propagation (BP) neural network-based prediction model was trained to predict BV for enhanced efficiency in subsequent work. The model was trained and calibrated, achieving a correlation coefficient (R) of 0.99 and a prediction accuracy of 95% on the test set. The results indicated that the BP neural network model using the Levenberg–Marquardt algorithm accurately predicted the forward breakdown voltage of the HBB-HEMT, underscoring the feasibility and significance of neural network models in designing GaN power devices. Full article

For operation as power amplifiers in RF applications, high electron mobility transistor (HEMT) structures are subjected to a range of bias conditions, applied at both the gate and drain terminals, as the device is biased from the OFF- to ON-state conditions. The stability of the device threshold voltage (V_t) condition is imperative from a circuit-design perspective and is the focus of this study, where stresses in both the ON and OFF states are explored. We see rapid positive threshold voltage increases under negative bias stress and subsequent recovery (i.e., V_t reduces), whereas conversely, we see a negative V_t shift under positive stress and V_t increase during the subsequent relaxation phase. These effects are correlated with the thickness of the GaN layer and ultimately result from the deep carbon-acceptor levels in the C-GaN back barrier incorporated to screen the buffer between the silicon substrate and the epitaxially grown GaN layer. Methods to mitigate this effect are explored, and the consequences are discussed. Full article