Reverse Gate Leakage Current Research Articles

Reduced trap state density in AlGaN/GaN HEMTs with low-temperature CVD-grown BN gate dielectric

In this Letter, low-temperature (400 °C) chemical vapor deposition-grown boron nitride (BN) was investigated as the gate dielectric for AlGaN/GaN metal–insulator–semiconductor high electron mobility transistors (MISHEMTs) on a Si substrate. Comprehensive characterizations using x-ray photoelectron spectroscopy, reflection electron energy loss spectroscopy, atomic force microscope, high-resolution transmission electron microscopy, and time-of-flight secondary ion mass spectrometry were conducted to analyze the deposited BN dielectric. Compared with conventional Schottky-gate HEMTs, the MISHEMTs exhibited significantly enhanced performance with 3 orders of magnitude lower reverse gate leakage current, a lower off-state current of 1 × 10−7 mA/mm, a higher on/off current ratio of 108, and lower on-resistance of 5.40 Ω mm. The frequency-dependent conductance measurement was performed to analyze the BN/HEMT interface, unveiling a low interface trap state density (Dit) on the order of 5 × 1011–6 × 1011 cm−2 eV−1. This work shows the effectiveness of low-temperature BN dielectrics and their potential for advancing GaN MISHEMTs toward high-performance power and RF electronics applications.

High-Performance N-Polar GaN/AlGaN Metal–Insulator–Semiconductor High-Electron-Mobility Transistors with Low Surface Roughness Enabled by Chemical–Mechanical-Polishing-Incorporated Layer Transfer Technology

High-Performance N-Polar GaN/AlGaN Metal–Insulator–Semiconductor High-Electron-Mobility Transistors with Low Surface Roughness Enabled by Chemical–Mechanical-Polishing-Incorporated Layer Transfer Technology

The isolation feature geometry dependence of reverse gate-leakage current of AlGaN/GaN HFETs

Reverse gate-leakage current of AlGaN/GaN heterojunction field-effect transistors (HFETs) realized on array of submicron sized fins and conventional mesa isolation feature geometries is investigated at room temperature and zero drain-source bias. For each of the abovementioned device categories, the significance of leakage from the top surface gate as well as gated etched GaN surfaces, especially sidewalls, is studied for a wide range of gate-source voltages (VGS) (i.e. below and above the threshold voltage). It is proven that in the explored fin-type HFETs, for all values of VGS leakage through the gated GaN surfaces, especially the sidewalls, is more significant than the leakage from the top surface gate. This is while in the mesa category, the sidewall leakage is of importance only at less negative values of VGS, and leakage from the top surface gate substantially takes over at more negative VGS values. The discrepancy in the dominance of the aforementioned leakage paths at more negative VGS values among the explored fin and mesa-type HFETs is demonstrated to be due to the stronger electric field across the barrier in the gated region of the mesa-type HFET for this range of VGS. While in the explored fin-type HFETs Ion/Ioff ratio is as high as 2 × 107, the total amount of reverse gate-leakage at all values of VGS is substantially larger compared to the mesa category sharing an equal value of the overall gate width, which substantiates the significance of leakage through etched GaN surfaces in devices composed of larger number of sidewalls, incorporating larger area of gate-overlapping etched GaN surface.

Remarkable Reduction in IG with an Explicit Investigation of the Leakage Conduction Mechanisms in a Dual Surface-Modified Al2O3/SiO2 Stack Layer AlGaN/GaN MOS-HEMT.

We demonstrated the performance of an Al2O3/SiO2 stack layer AlGaN/GaN metal-oxide semiconductor (MOS) high-electron-mobility transistor (HEMT) combined with a dual surface treatment that used tetramethylammonium hydroxide (TMAH) and hydrochloric acid (HCl) with post-gate annealing (PGA) modulation at 400 °C for 10 min. A remarkable reduction in the reverse gate leakage current (IG) up to 1.5×10-12 A/mm (@ VG = -12 V) was observed in the stack layer MOS-HEMT due to the combined treatment. The performance of the dual surface-treated MOS-HEMT was significantly improved, particularly in terms of hysteresis, gate leakage, and subthreshold characteristics, with optimized gate annealing treatment. In addition, an organized gate leakage conduction mechanism in the AlGaN/GaN MOS-HEMT with the Al2O3/SiO2 stack gate dielectric layer was investigated before and after gate annealing treatment and compared with the conventional Schottky gate. The conduction mechanism in the reverse gate bias was Poole-Frankel emission for the Schottky-gate HEMT and the MOS-HEMT before annealing. The dominant conduction mechanism was ohmic/Poole-Frankel at low/medium forward bias. Meanwhile, gate leakage was governed by the hopping conduction mechanism in the MOS-HEMT without gate annealing modulation at a higher forward bias. After post-gate annealing (PGA) treatment, however, the leakage conduction mechanism was dominated by trap-assisted tunneling at the low to medium forward bias region and by Fowler-Nordheim tunneling at the higher forward bias region. Moreover, a decent product of maximum oscillation frequency and gate length (fmax × LG) was found to reach 27.16 GHz∙µm for the stack layer MOS-HEMT with PGA modulation. The dual surface-treated Al2O3/SiO2 stack layer MOS-HEMT with PGA modulation exhibited decent performance with an IDMAX of 720 mA/mm, a peak extrinsic transconductance (GMMAX) of 120 mS/mm, a threshold voltage (VTH) of -4.8 V, a higher ION/IOFF ratio of approximately 1.2×109, a subthreshold swing of 82 mV/dec, and a cutoff frequency(ft)/maximum frequency of (fmax) of 7.5/13.58 GHz.

Mechanism of reverse gate leakage current reduction in AlGaN/GaN high-electron-mobility-transistor after 3-MeV proton irradiation

A 3-MeV proton irradiation experiment was carried out on an AlGaN/GaN high-electron-mobility-transistor (HEMT). The results showed that the device's saturation drain current decreased, the threshold voltage drifted positively, and the maximum transconductance decreased after irradiation. Interestingly, the forward gate leakage current was almost unchanged, and the reverse gate leakage current was reduced by two orders of magnitude. We found that this experimental phenomenon can be well explained by the Poole–Frenkel emission model. Proton irradiation led to deeper defect energy levels and higher defect concentrations of the device. Deeper defect energy levels made it more difficult for electrons to be excited from the trap state into the conduction band. Thus, the reverse gate leakage current decreased. Higher defect concentrations led to degradation of the output and transfer curves of the device. The deep level transient spectroscopy characterization defect further proved the correctness of this model. The reduction in the reverse gate leakage current had a positive impact on AlGaN/GaN HEMT devices in high power or high frequency applications.

Reverse gate leakage mechanism of AlGaN/GaN HEMTs with Au-free gate

The reverse gate leakage mechanism of W-gate and TiN-gate AlGaN/GaN high-electron-mobility transistors (HEMTs) with N2 plasma surface treatment is investigated using current–voltage (I–V) and capacitance–voltage (C–V) characteristics and theoretical calculation analysis. It is found that the main reverse gate leakage mechanism of both devices is the trap-assisted tunneling (TAT) mechanism in the entire reverse bias region (–30 V to 0 V). It is also found that the reverse gate leakage current of the W-gate AlGaN/GaN HEMTs is smaller than that of the TiN gate at high reverse gate bias voltage. Moreover, the activation energies of the extracted W-gate and TiN-gate AlGaN/GaN HEMTs are 0.0551 eV–0.127 eV and 0.112 eV–0.201 eV, respectively.

Proton-Induced Effect on AlGaN/GaN HEMTs After Hydrogen Treatment

The effect of proton irradiation on the electrical properties of AlGaN/GaN high electron mobility transistors (HEMTs) with hydrogen treatment is studied. Hydrogen treatment makes the damage caused by proton irradiation worse. The AlGaN/GaN HEMTs with hydrogen treatment at 2.0 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14 </sup> p/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> 3-MeV proton irradiation fluence experience a decrease by 37.3% in the saturation current, a 0.55V positive shift of the threshold voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> ) and a notable decrease in reverse gate leakage current. While the AlGaN/GaN HEMTs without hydrogen treatment experience a decrease by 18.2% in the saturation current, a 0.211V positive shift of the V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> . After extracted by the Low Frequency Noise method (LFN method), the flat-band voltage noise power spectral density (S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Vfb</sub> ) after hydrogen treatment decreases, and proton irradiation makes the number of defects increased. But the hydrogen treatment causes the S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Vfb</sub> to rise rapidly after proton irradiation, comparing with the AlGaN/GaN HEMTs without hydrogen treatment. The main mechanism can be attributed to the hydrogen passivation defect and proton irradiation to stimulate the passivation defect to produce composite defects. And the AlGaN/GaN HEMTs with hydrogen treatment is more sensitive to proton irradiation, compared with the AlGaN/GaN HEMTs without hydrogen treatment.

Effect of Hydrostatic Pressure on the Revers Gate-Current of AlGaN/GaN HEMTs

In this paper, we present an Analytical-Numerical model for reverse gate leakage current in AlGaN/GaN high electron mobility transistors (HEMTs), which investigate the influence of the hydrostatic pressure (HP) on gate-current. Salient features of the model are incorporated of occupied sub-bands in the interface quantum well, combined with a self-consistent solution of the Schrödinger and Poisson equations. Finite difference techniques have been used to acquire energy eigenvalues and their corresponding eigenfunctions of AlGaN/GaN (HEMTs). It has been found that the bound charge at the heterointerface has the most impact on the threshold voltage. The increases in hydrostatic pressure cause an increase in threshold voltage. With increasing HP, the Schottky barrier height decreases, AlGaN electric field and reverse gate leakage current are increased. The increase in HP acts as a positive virtual gate. The dependence on the HP of Poole- Frenkel emission (FP) and Fowler-Nordheim (FN) direct tunneling is more than trap-assisted-tunneling (TAT). Increasing the pressure of 2GPa, the intersection point of PF and TAT varies by 1 volt, the reverse gate current increases by an average of 35%, and the threshold voltage increases to 1.15 V in absolute terms.

DC performance improvement of nanochannel AlGaN/AlN/GaN HEMTs with reduced OFF-state leakage current by post-gate annealing modulation

In this work, the effects of a post-gate annealing (PGA) treatment on the electrical performance of AlGaN/AlN/GaN nanochannel high electron mobility transistors (NC-HEMTs) were analyzed, with various channel widths of 200, 400, 600, and 800 nm for a constant fill factor of 0.45. A systematic improvement in the DC parameters was observed in the NC-HEMTs after PGA treatment at 400 °C for 10 min. Secondary ion mass spectroscopy was performed on the 300 °C, 400 °C, and 500 °C for 10 min annealed and as-deposited NC-HEMT to optimize the PGA conditions. It was also verified that annealing at higher temperatures (>400 °C) can cause the diffusion of the gate metal (Ni/Au) into the AlGaN/AlN/GaN active layer, which subsequently degrades the device performance. The removal of shallow traps after the PGA treatment, which were created by ICP dry etching, improved the Schottky barrier height () from 0.42 eV to 1.40 eV and resulted in a significant reduction in the reverse gate leakage current (I G) of approximately more than three orders of magnitude in the NC-HEMT with a channel width of 200 nm. The reduction in the channel resistance after the PGA treatment, correspondingly improved the drift velocity, resulting in a marked improvement in the maximum transconductance (G MMAX) of 34% and considerable incremental increases in the maximum drain current (I DMAX). The NC-HEMT (W NC = 200 nm) with PGA treatment exhibited decent performance, with an I G of 9 A mm−1, an I DMAX of 470 mA mm−1, a G MMAX of 140 mS mm−1, and an ON/OFF ratio (I ON/I OFF) of approximately along with improved gate controllability, i.e. lowering of the subthreshold swing to 69 mV dec−1.

Single-Event Damage-Induced Gate-Leakage Mechanisms in AlGaN/GaN High-Electron-Mobility Transistors

Heavy ion-induced electrical degradations and mechanisms of high-electron-mobility transistors (HEMTs) were investigated in this article. AlGaN/GaN HEMTs were irradiated by 800-MeV Bi ions with total fluence of 5.23×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> ions/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The results show that the saturation current decreased by 13.1%, the threshold voltage negatively shifted by 0.21 V, the peak transconductance decreased by 26.6%, the reverse gate-leakage current increased much more than 16 times, and forward gate-leakage current increased more than three times. Furthermore, all electrical performances experienced partial recovery after room temperature annealing (RTA) and 175 °C thermal annealing except gate-leakage current. To further explore the mechanism of gate-leakage degradation, AlGaN/GaN heterojunction wafers were exposed to 1400-MeV Ta ions with fluence of 6.86×107 ions/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and characterized by conductive atomic force microscope (CAFM) before and after the irradiation. The results show that the leakage current significantly increased in AlGaN material areas after the irradiation. Comparing the increase in gate leakage of the AlGaN/GaN heterojunction and AlGaN/GaN HEMT induced by heavy ions irradiation, it can be seen that the gate-leakage current of AlGaN/GaN HEMT after heavy irradiation almost entirely was caused by latent tracks. The mechanism for the irreversible increase in gate leakage after heavy ions irradiation could be attributed to the latent tracks along the ion trajectories through the heterojunction.

Drain-Bias-Dependent Study of Reverse Gate-Leakage Current in AlGaN/GaN HFETs

Reverse gate-leakage of the AlGaN/GaN heterostructure field-effect transistors (HFETs) is studied at different values of drain–source voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {DS}}$ </tex-math></inline-formula> ), ranging from 0 to 10 V. Throughout the investigated range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {DS}}$ </tex-math></inline-formula> , the reported analysis confirms the applicability of the Fowler–Nordheim (FN) tunneling as the dominant contributor to the gate-leakage for reverse gate biases until the onset of the threshold voltage. Device simulations were performed using Comsol Multiphysics to estimate the electric field ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E\,\,$ </tex-math></inline-formula> ) across the polar III-nitride barrier layer at different positions along the gate length. We observe that the FN tunneling takes place predominantly corresponding to the average electric field observed to be close to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E} $ </tex-math></inline-formula> at the center of the gate for lower values of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {DS}}$ </tex-math></inline-formula> , whereas at larger values of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {DS}}$ </tex-math></inline-formula> , FN tunneling corresponding to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}$ </tex-math></inline-formula> only at the drain edge of the gate seems poised to deliver the gate-leakage current. In formulating the FN tunneling, the value of the electron effective mass is selected consistently within an acceptable range for analyzing gate-leakage. Investigating the applicability of FN tunneling in explaining the reverse gate-leakage current of AlGaN/GaN HFETs for the aforementioned values of gate to source voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {GS}}$ </tex-math></inline-formula> ) not just at zero <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {DS}}$ </tex-math></inline-formula> , but across a range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {DS}}$ </tex-math></inline-formula> values, seems to offer a more convincing argument for the hypothesis on tunneling through small leakage zones.

Investigation of threshold voltage shift and gate leakage mechanisms in normally off AlN/Al0.05Ga0.95N HEMTs on Si substrate

In this study, normally off AlN/Al0.05Ga0.95N high-electron-mobility transistors (HEMTs) on a Si substrate were fabricated by adjusting the surface states of the heterostructure. The device exhibited an extremely low reverse gate leakage current of 10−7 mA/mm due to the high Schottky-barrier height for Ni/Au on AlN/Al0.05Ga0.95N. A high ION/IOFF of 108 and a low subthreshold slope of 63 mV/decade were attained for this device. Moreover, breakdown voltages of 665 V and 1000 V were reached in these devices, with a gate-to-drain distance of 26 µm, for a grounded substrate and a floating substrate, respectively. In order to evaluate the reliability of the device, bias-induced and temperature-induced threshold-voltage-instabilities were investigated. The threshold voltage of the device shifted with gate bias stress due to electrons in the channel trapped by bulk traps. Thermally activated electrons releasing from traps decreased the threshold voltage with increasing measurement temperature. This indicates that the reliability in the threshold-voltage stability for the normally off device is dominated by the deep traps in epitaxially grown AlN/Al0.05Ga0.95N. Finally, the gate leakage mechanisms in AlN/Al0.05Ga0.95N HEMTs were investigated. The reverse and forward gate leakage was dominated by Poole–Frenkel tunneling and thermionic emission, respectively.

Improving Current ON/OFF Ratio and Subthreshold Swing of Schottky- Gate AlGaN/GaN HEMTs by Postmetallization Annealing

Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -passivated Schottky-gate AlGaN/GaN high electron mobility transistors (HEMTs) with improved subthreshold swing (SS) and drain current ON/OFF ratio by postmetallization annealing (PMA) at 500 °C in N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ambient are reported. With the PMA, the gate leakage current in the reverse biased region and the OFF-state drain current are reduced by more than three orders of magnitude, leading to a low SS of 84.75 mV/dec and a high drain current ON/OFF ratio of 2.1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> . Through temperature-dependent current-voltage measurements on dual-Schottky-gate structures and capacitance-voltage measurements on Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /AlGaN/GaN metal-insulator-semiconductor (MIS) HEMT capacitors, it is identified that the PMA greatly suppresses both the Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /AlGaN interface leakage current and the reverse gate leakage current by eliminating Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /AlGaN interface trap states with 0.34 eV trap state energy and changing the dominant mechanism of reverse gate leakage conduction from trap-assisted tunneling to Fowler-Nordheim tunneling, respectively. Overall, this work reports on the effectiveness of PMA in improving the performance of Schottky-gate AlGaN/GaN HEMTs and the underlying improving mechanisms.

AlN/GaN HEMT with Gate Insulation and Current Collapse Suppression Using Thermal ALD ZrO2

In this letter, we report the device characteristics of AlN/GaN MIS-HEMT on silicon substrate using thermal atomic-layer-deposition (ALD) ZrO2 with various thicknesses. The thermal ALD ZrO2 thin film is deposited at 250°C, which avoids plasma enhancement during the fabrication process. From the transmission electron microscopy results, it is found that the alloy penetrates to the 2DEG region to form a carrier conductive pathway which facilitates the ohmic contact formation. The optimized 7 nm-thick ZrO2 AlN/GaN MIS-HEMT exhibits improved Ion/Ioff ratio and suppressed current collapse degradation, compared with 4 nm-thick ZrO2 AlN/GaN MIS-HEMT and Schottky gate AlN/GaN HEMT (SG-HEMT). In addition, as compared to SG-HEMT, reverse gate leakage current can be reduced by about six orders and forward gate bias extends to + 6.3 V with 7 nm-thick ZrO2 AlN/GaN MIS-HEMT.

Mechanism of high-fluence proton induced electrical degradation in AlGaN/GaN high-electron-mobility transistors

The effects of displacement damage induced by 3 and 6 MeV protons in AlGaN/GaN high-electron-mobility transistors (HEMTs) are investigated. For the 6 MeV protons at a dose of 5 × 1014 cm−2, a 12% decrease in saturation current, a 3.8% decrease in the peak transconductance, a 0.3 V positive shift of the threshold voltage, and a three-to fourfold decrease in reverse gate leakage current are observed compared with the pre-irradiation values. The main degradation mechanism is considered to be the generation of deep trap states in the band gap, which remove electrons and reduce the carrier mobility in a two-dimensional electron gas (2DEG). Both the carrier removal rate and negatively charged trap density can be extracted, which shows that about 3500 proton injections lead to one carrier removal. Proton fluence and energy are found to be two key parameters that affect the degradation characteristics of irradiated GaN HEMTs.

Analysis of reverse gate leakage mechanism of AlGaN/GaN HEMTs with N2 plasma surface treatment

The mechanism of reverse gate leakage current of AlGaN/GaN HEMTs with two different surface treatment methods are studied by using C-V, temperature dependent I–V and theoretical analysis. At the lower reverse bias region (VR >− 3.5 V), the dominant leakage current mechanism of the device with N2 plasma surface treatment is the Poole-Frenkel emission current (PF), and Trap-Assisted Tunneling current (TAT) is the principal leakage current of the device which treated by HCl:H2O solution. At the higher reverse bias region (VR <− 3.5 V), both of the two samples show good agreement with the surface leakage mechanism. The leakage current of the device with N2 plasma surface treatment is one order of magnitude smaller than the device which treated by HCl:H2O solution. This is due to the recovery of Ga-N bond in N2 plasma surface treatment together with the reduction of the shallow traps in post-gate annealing (PGA) process. The measured results agree well with the theoretical calculations and demonstrate N2 plasma surface treatment can reduce the reverse leakage current of the AlGaN/GaN HEMTs.

Achievement of normally-off AlGaN/GaN high-electron mobility transistor with p-NiOx capping layer by sputtering and post-annealing

In this paper, we present a technique to fabricate normally off GaN-based high-electron mobility transistor (HEMT) by sputtering and post-annealing p-NiOx capping layer. The p-NiOx layer is produced by sputtering at room temperature and post-annealing at 500°C for 30min in pure O2 environment to achieve high hole concentration. The Vth shifts from −3V in the conventional transistor to 0.33V, and on/off current ratio became 107. The forward and reverse gate breakdown increase from 3.5V and −78V to 10V and −198V, respectively. The reverse gate leakage current is 10−9A/mm, and the off-state drain-leakage current is 10−8A/mm. The Vth hysteresis is extremely small at about 33mV. We also investigate the mechanism that increases hole concentration of p-NiOx after annealing in oxygen environment resulted from the change of Ni2+ to Ni3+ and the surge of (111)-orientation.

Impact Ionization in SOI MESFETs at the 32-nm Node

Silicon metal–semiconductor FETs (MESFETs) have been fabricated using a 32-nm silicon-on-insulator (SOI) CMOS technology. The MESFET gates are formed during the self-aligned silicide step and show almost ideal Schottky behavior at low drain voltages. However, an anomalous peak in the reverse gate leakage current appears for drain voltages ≥2 V. The anomalous gate current is attributed to impact ionization generating excess holes that exit the channel through the Schottky contact. An analytical model is used to extract the electron impact ionization rate, $\alpha $ , which agrees with three earlier data sets over nearly four orders of magnitude.

Influence of the gate edge on the reverse leakage current of AlGaN/GaN HEMTs

By comparing the Schottky diodes of different area and perimeter, reverse gate leakage current of AlGaN/GaN high mobility transistors (HEMT) at gate bias beyond threshold voltage is studied. It is revealed that reverse current consists of area-related and perimeter-related current. An analytical model of electric field calculation is proposed to obtain the average electric field around the gate edge at high revers bias and estimate the effective range of edge leakage current. When the reverse bias increases, the increment of electric field is around the gate edge of a distance of ΔL, and perimeter-related gate edge current keeps increasing. By using the calculated electric field and the temperature-dependent current-voltage measurements, the edge gate leakage current mechanism is found to be Fowler-Nordheim tunneling at gate bias bellows -15V caused by the lateral extended depletion region induced barrier thinning. Effective range of edge current of Schottky diodes is about hundred to several hundred nano-meters, and is different in different shapes of Schottky diodes.

Effect of proton irradiation energy on AlGaN/GaN metal-oxide semiconductor high electron mobility transistors

The effects of proton irradiation energy on dc characteristics of AlGaN/GaN metal-oxide semiconductor high electron mobility transistors (MOSHEMTs) using Al2O3 as the gate dielectric were studied. Al2O3/AlGaN/GaN MOSHEMTs were irradiated with a fixed proton dose of 5 × 1015 cm−2 at different energies of 5, 10, or 15 MeV. More degradation of the device dc characteristics was observed for lower irradiation energy due to the larger amount of nonionizing energy loss in the active region of the MOSHEMTs under these conditions. The reductions in saturation current were 95.3%, 68.3%, and 59.8% and reductions in maximum transconductance were 88%, 54.4%, and 40.7% after 5, 10, and 15 MeV proton irradiation, respectively. Both forward and reverse gate leakage current were reduced more than one order of magnitude after irradiation. The carrier removal rates for the irradiation energies employed in this study were in the range of 127–289 cm−1. These are similar to the values reported for conventional metal-gate high-electron mobility transistors under the same conditions and show that the gate dielectric does not affect the response to proton irradiation for these energies.