Characteristics Of High Electron Mobility Transistors Research Articles

Effect of Acceptor Traps in GaN Buffer Layer on Source/Drain Contact Resistance in AlGaN/GaN High Electron Mobility Transistors

As‐grown GaN buffer layers have a significant electron concentration, which causes an increase in leakage current and a decrease in the breakdown voltage, VBR, of GaN High Electron Mobility Transistors (HEMTs). To prevent this, deep acceptor traps of density, NAT, are added to the GaN layer during growth. While a study on the effect of NAT on VBR is available in the literature, that on the effect of NAT on contact resistance, Rc, of source/drain contacts is lacking. Herein, the following is established using technology computer‐aided design simulations calibrated with measured current–voltage characteristics of ungated AlGaN/GaN structures: 1) Rc increases significantly with NAT and with the depth of the trap level from the conduction band. For trap level 2.5 eV below the conduction band, Rc doubles for an increase in NAT from 1 × 1016 to 5 × 1017 cm−3. 2) The variation of Rc with temperature is non‐monotonic. Over a temperature range of 300–450 K, Rc is nearly constant with temperature for NAT = 1 × 1016 cm−3 and decreases by 20% for NAT = 5 × 1017 cm−3, when traps are 2.5 eV below the conduction band. Also, the degradation of the transfer and output characteristics of GaN HEMTs due to a notable increase in Rc due to NAT is investigated.

Review on Main Gate Characteristics of P-Type GaN Gate High-Electron-Mobility Transistors.

As wide bandgap semiconductors, gallium nitride (GaN) lateral high-electron-mobility transistors (HEMTs) possess high breakdown voltage, low resistance and high frequency performance. PGaN gate HEMTs are promising candidates for high-voltage, high-power applications due to the normally off operation and robust gate reliability. However, the threshold and gate-breakdown voltages are relatively low compared with Si-based and SiC-based power MOSFETs. The epitaxial layers and device structures were optimized to enhance the main characteristics of pGaN HEMTs. In this work, various methods to improve threshold and gate-breakdown voltages are presented, such as the top-layer optimization of the pGaN cap, hole-concentration enhancement, the low-work-function gate electrode, and the MIS-type pGaN gate. The discussion of the main gate characteristic enhancement of p-type GaN gate HEMTs would accelerate the development of GaN power electronics to some extent.

Analysis of Trapping Effect on Large-Signal Characteristics of GaN HEMTs Using X-Parameters and UV Illumination.

GaN high-electron-mobility transistors (HEMTs) have attracted widespread attention for high-power microwave applications, owing to their superior properties. However, the charge trapping effect has limitations to its performance. To study the trapping effect on the device large-signal behavior, AlGaN/GaN HEMTs and metal-insulator-semiconductor HEMTs (MIS-HEMTs) were characterized through X-parameter measurements under ultraviolet (UV) illumination. For HEMTs without passivation, the magnitude of the large-signal output wave (X21FB) and small-signal forward gain (X2111S) at fundamental frequency increased, whereas the large-signal second harmonic output wave (X22FB) decreased when the device was exposed to UV light, resulting from the photoconductive effect and suppression of buffer-related trapping. For MIS-HEMTs with SiN passivation, much higher X21FB and X2111S have been obtained compared with HEMTs. It suggests that better RF power performance can be achieved by removing the surface state. Moreover, the X-parameters of the MIS-HEMT are less dependent on UV light, since the light-induced performance enhancement is offset by excess traps in the SiN layer excited by UV light. The radio frequency (RF) power parameters and signal waveforms were further obtained based on the X-parameter model. The variation of RF current gain and distortion with light was consistent with the measurement results of X-parameters. Therefore, the trap number in the AlGaN surface, GaN buffer, and SiN layer must be minimized for a good large-signal performance of AlGaN/GaN transistors.

Influence of Fin-Like Configuration on Small-Signal Performance of AlGaN/GaN HEMTs

In this work, a new small-signal model (SSM), which is called the distributes intrinsic subdevice model (DISDM), is established for AlGaN/gallium nitride (GaN) Fin-like high-electron mobility transistors (HEMTs) according to the device structure feature. Perfect agreements between the measured and simulated scattering parameters (S-parameters) illustrated the validity of the DISDM and the accuracy of parameters extracted from the new model. Then, the characteristics of Fin-like HEMTs are analyzed using the DISDM theoretically. Different from the traditional model, the DISDM can accurately show the characteristics of the Fin-like HEMTs, especially the “double-peak” of the intrinsic transconductance. Compared with the planar HEMTs, the Fin-like HEMTs exhibit a higher linearity in direct current and small-signal parameters. For Fin-like HEMTs with different recess depths and duty ratios, the variation of the small-signal parameters and the linearity of devices were characterized to evaluate the performance of devices and optimize the process in the end.

DC and low-frequency noise characteristics of GaN-based HEMTs under cryogenic temperatures

In this work, the device characteristics of GaN-based high-electron-mobility transistors (HEMTs) were systematically investigated by the direct current (DC) and low-frequency noise (LFN) measurements within the temperature ranging from 300 K to 4.2 K. The temperature-dependent behavior of the on- and off-state electrical properties was statistically analyzed, highlighting an overall improved device performance under cryogenic temperatures. In addition, the LFN of the device exhibited an evident behavior of 1/f noise from 10 Hz to 10 kHz in the measured temperature range and can be well described by the carrier number fluctuations with correlated mobility fluctuations (CNF/CMF) model down to 4.2 K. Based on this model, we further extracted and discussed the defect-related behavior in the devices under low-temperature environments. These experimental results provide insights into the device characteristics of GaN-based HEMTs under cryogenic environments, motivating further studies into the GaN-based cryo-devices and systems.

Effect of amorphous ternary AlBN passivations on the performance of AlGaN/GaN HEMTs

In this article, an amorphous ternary AlBN dielectric passivation layer is proposed for GaN/AlGaN high-electron mobility transistors (HEMTs). The source–gate–drain access regions with both AlBN and AlN amorphous dielectric films deposited by pulsed laser deposition are investigated to understand their effects on the device performance. Compared with the AlN-passivated HEMTs, the electrical characteristics of AlBN-passivated HEMTs are significantly improved with the same passivation layer thickness. An increase in maximum drain saturation current of AlBN-passivated HEMTs is ∼19.74% at Vgs = 2 V, and the corresponding peak extrinsic transconductance is improved by 38.08% at Vgs = −2 V and Vds = 2 V. Such excellent properties are ascribed to large surface potential change, due to the effect of boron dopants on AlBN films.

Impact of AlGaN Barrier Thickness and Substrate Material on the Noise Characteristics of GaN HEMT

In this paper, the impact of AlGaN barrier thickness (tAlGaN) and substrate leakage on the noise conductance and noise figure in GaN High Electron Mobility Transistor (HEMT) is investigated. The investigation and analysis in this paper are targeting the Low Noise Amplifier (LNA) applications. The noise analysis is carried out using Technology Computer-Aided Design (TCAD) physical simulator. Initially, the DC, RF, and noise simulations are validated against measurements of a GaN device. AlGaN barrier thickness (tAlGaN) is varied and its impact on the minimum noise figure (NFmin) is analyzed. It is observed that the NFmin decreases with tAlGaN reduction at the typical bias conditions of LNA. This observation on the impact of tAlGaN on the NFmin follows Fukui’s model, which states that the NFmin decreases with the increase in transconductance. In addition, the impact of the substrate material on noise performance is analyzed. The substrates used for the investigation are Silicon (Si) and Silicon Carbide (SiC). At 40 GHz, it is found that the noise conductance and the NFmin of GaN HEMT on SiC substrate is reduced by 13% and 12%, respectively, in comparison with GaN HEMT on Si substrate. This could be attributed to the lower gate-to-substrate capacitance of the GaN HEMT on SiC substrate.

Study of Normally-Off AlGaN/GaN HEMT with Microfield Plate for Improvement of Breakdown Voltage.

In this paper, we introduce a new type of AlGaN/GaN high electron mobility transistor (HEMT) with microfield plate (FP). We use Silvaco-ATLAS two-dimensional numerical simulation to calculate the performance of conventional HEMT and HEMT with micro-FP and analyze its principle. By studying a new charge balance method provided by HEMTs and micro-FPs, the physical mechanism of FP adjusting the HEMT potential distribution and channel electric field distribution is analyzed. The new FP structure consists of a drain field plate (D-FP), a source field plate (S-FP) and several micro-gate field plates (G-FP) to improve the output characteristics of HEMTs. By adjusting the distribution of potential and channel electric field, a wider and more uniform channel electric field can be obtained, and the breakdown voltage can be increased to 1278 V. Although the on-resistance of the HEMT is slightly increased to 5.24 mm, it is still lower than other reference values. These results may open up a new and effective method for manufacturing high-power devices for power electronics applications.

Study on positive threshold voltage shift and DC characteristics of HEMTs using gate recess technique

In the present study, AlGaN/GaN high-electron-mobility transistors (HEMTs) were fabricated through metal–organic chemical vapor deposition. Gate recess etching, combined with inductively coupled plasma reactive ion etching, was adopted, and etching time was controlled to manipulate the threshold voltage [Formula: see text]. The DC characteristics of devices etched for 0–25 s were investigated. [Formula: see text] exhibited a 1.9-V positive shift in the device with the AlGaN layer etched for 25 s. The effect of an AlN buffer layer on the [Formula: see text] shift was also investigated. The [Formula: see text] of the HEMT etched for 25 s and without an AlN buffer layer exhibited a positive shift of 3.1 V.

Epi-Gd₂O₃-MOSHEMT: A Potential Solution Toward Leveraging the Application of AlGaN/GaN/Si HEMT With Improved I ON/I OFF Operating at 473 K

In this article, we report the temperature-dependent transistor characteristic of Epi-Gd <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 oxide semiconductor high electron mobility transistor (MOSHEMT) and compare its properties with that of AlGaN/GaN metal-Schottky high electron mobility transistor (HEMT) grown on 150 mm Si (111) substrate. Introducing an epitaxial single crystalline Gd <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> between the metal gate and AlGaN barrier not only improves the gate leakage current significantly but also enhances its thermal stability. We observe that there is no significant change in the gate leakage current even at 473 K compared to that measured at room temperature (RT) (298 K), and this is also evident in the transistor's subthreshold behavior at 473 K. We have determined the electric field within the Gd <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> as well as AlGaN and investigated the leakage conduction mechanism through Gd <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> . The I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> ON</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> OFF</sub> of the transistor was measured as high as ~10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> even at 473 K with the lowest V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> shift (91.4 mV) with temperature. Our measurements also confirm the presence of polar optical phonon scattering, which directly affects the 2-D electron gas (2DEG) mobility at high temperatures and thus the electrical characteristics of HEMT and MOSHEMT.

AlN/GaN Superlattice Channel HEMTs on Silicon Substrate

High-electron-mobility transistor (HEMT) with AlN/GaN superlattice (SL) channel has been demonstrated on a silicon substrate. High OFF-state breakdown voltage ${V}_{\text {BR}}$ of 670 V (gate–drain spacing ${L}_{\text {GD}} = 8\,\,\mu \text{m}$ ) along with a maximum output current of 196 mA/mm, a channel electron total mobility of 507 cm2/ $\text{V}\cdot \text{s}$ , and an ON/ OFF ratio of over 107 was achieved in this novel HEMT. For the HEMT with ${L}_{\text {GD}} = 22\,\,\mu \text{m}$ , a high ${V}_{\text {BR}}$ of 1700 V was obtained with substrate floated. The influence of ${L}_{\text {GD}}$ , the gate–source voltage ${V}_{\text {GS}}$ , the isolated pattern, and substrate grounded and floated type was discussed to analyze the breakdown characteristics of HEMT. We investigated the trap states in the AlN/GaN SL channel of HEMTs by frequency-dependent capacitance and conductance measurements. A trap state density of $7.4\times 10^{{12}}$ – $1.2\times 10^{{13}}$ cm−2eV−1 is located at ${E}_{\text {T}}$ in a range of 0.29–0.33 eV of the main channel, while the trap state density in the parasitic channel decreases from $3.9\times 10^{{11}}$ cm−2eV−1 at an energy of 0.27 eV to $1.1\times 10^{{11}}$ cm−2eV−1 at an energy of 0.38 eV. The fabricated AlN/GaN SL channel HEMTs in this work reveal a great step toward the realization of the SL channel HEMTs on cost-effective silicon substrate and provide a novel technology for AlGaN multichannel devices to obtain high output current.

Effect of Fixed Charges at Interface Between InP and Bonding Layer on Heterogeneous Integration of InP HEMTs

DC performances of depletion-mode 100 nm In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As/InP high electron mobility transistor (HEMT) heterogeneously integrated to silicon substrate by SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> bonding were investigated by using numerical simulation. Effects of fixed charges at the InP/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> interface, the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> bonding interface, and the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Si interface on HEMT are compared. Among these charges, dc characteristics of HEMT are most sensitive to fixed charges at the InP/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> interface. With the density of negative fixed charges at the InP/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> interface increasing from - 5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> to - 1×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> , the energy band exhibits an upward bending and leads to a decrease of electron concentration in the channel. The threshold voltage shifts from -1.03 to -0.85 V and the output current exhibits a decrease of 96 mA/mm under the gate bias of 0 V; meanwhile, the breakdown voltage increases from 4.4 to 6.5 V under the gate bias of -1.6 V. A shift of C- V curves in pace with transfer characteristic curves further confirms that the two-dimensional electron gas (2DEG) channel of HEMT is indeed influenced by fixed charges at the InP/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> interface. As a comparison, the other two charges exhibit a relatively weak influence, where the increase of charges at the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> bonding interface results in a 36 mV shift of threshold voltage and 20 mA/mm decrease of output current, and the charges at the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Si interface only cause 6 mV shift of threshold that can almost be ignored. We proposed an appropriate increase of InP layer thickness to mitigate the impact of fixed charges on the transfer and output characteristic of HEMTs.

Mechanism of Proton-Induced electrical degradation of AlGaN/GaN high electron mobility transistors

We studied the mechanism of the proton-induced electrical degradation of AlGaN/GaN high electron mobility transistors (HEMTs) through 5-MeV proton irradiation. First, the AlGaN/GaN heterostructure was exposed to protons with a fluence of 1 × 1015p/cm2 to investigate the relationship between the radiation-caused damage in the heterostructure and the electrical characteristics of HEMTs. The HEMTs fabricated on a proton-irradiated AlGaN/GaN heterostructure showed slight degradation in dc characteristics and a positive shift in threshold voltage, compared with the HEMTs fabricated on an unirradiated heterostructure. This indicated that the proton radiation-induced defects in the AlGaN/GaN heterostructure were not dominant factors of characteristic degradation. After additional proton irradiation into both devices, more severe degradation in electrical characteristics was confirmed. The HEMTs fabricated on a proton-irradiated heterostructure showed the largest characteristic degradation in this work. It is expected that the secondary particles, attributed from the collision of proton and metal contacts such as ohmic and schottky, can cause the creation of additional defects, leading to significant degradation of device characteristics. In addition, the pre-existing defects in AlGaN/GaN heterostructures created first proton irradiation can also influence the characteristic degradation of devices.

Fabrication and characteristics of flexible normally-off AlGaN/GaN HEMTs

In this paper, we present a method for removing a high electron mobility transistor (HEMT) silicon substrate using mechanical grinding and deep silicon etching technology and successfully transferred the epitaxial wafer to a PET substrate to achieve the flexible normally-off HEMT. By testing the output characteristics and transfer characteristics of the Si-substrate HEMT and PET-substrate HEMT, we have demonstrated that the PET-substrate HEMT has excellent performance and successfully achieved the mechanical flexibility. Furthermore, we analyzed the physical mechanisms of the change in PET-substrate and Si-substrate HEMT characteristics, as well as flexible HEMT performance under bent and flattened states. The flexible HEMT array demonstrates significant potential in integration with other flexible devices, such as GaN-based micro-LED arrays.

A Novel Physics-Based Approach to Analyze and Model E-Mode p-GaN Power HEMTs

In this article, a physics-based analytical model which considers the channel charge ( Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ch</sub> ) for enhancement-mode p-GaN power high-electron-mobility transistors (HEMTs) is developed. First, by considering the same dynamic channel charge ( dQ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ch</sub> ) for the Schottky/p-GaN junction capacitance ( C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j,Sch</sub> ) and the p-i-n-junction capacitance ( C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p-i-n</sub> ), due to the p-GaN/AlGaN junction and two-dimensional electron gas (2DEG) charge, the analytical formula to calculate the voltage drop in the p-GaN layer ( V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pGaN</sub> ) is presented. Second, by implementing the analytical formulae in the advanced SPICE model (ASM) GaN model, the proposed physics-based model reliably fits the measured C- V and I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> - V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> characteristics of the samples under different processing conditions. This provides significant insight regarding the Mg concentration, the voltage drop at the Schottky metal/p-GaN junction ( V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j,Sch</sub> ), and the voltage drop at the p-GaN/AlGaN junction ( V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p-i-n</sub> ). Finally, the I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> - V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> and I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> - V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> characteristics of enhancement-mode p-GaN power HEMTs are modeled, displaying good agreement with the experimental data.

Effect of InGaN/GaN superlattice as underlayer on characteristics of AlGaN/GaN HEMT

The impact of an InGaN/GaN superlattice (SL) on AlGaN/GaN high electron mobility transistor characteristics was investigated, and two effects were discovered: one is a substantial improvement in the conduction characteristics as a result of the InGaN/GaN channel layer, while the other is the effect of diffusion suppression relating to impurities or point defects from the carbon-doped layer. The InGaN/GaN SL was used as a channel layer to improve the mobility and concentration of the two-dimensional channel electron gas. It was found that by inserting the InGaN/GaN SL just above a C-doped semi-insulating GaN layer as the InGaN underlayer, the conduction current of the SL with five periods (5SL) was observed to be much higher than that of the conventional material with a GaN channel layer of over 2 μm in thickness. The results demonstrated that this SL layer is effective in suppressing the diffusion of impurities or point defects originating from the carbon-doped layer, resulting in the device performance improvement.

Thermal analysis of GaN-on-SiC HEMTs with different backside via layouts

Temperature dependent electrical characteristics of GaN-on-SiC high-electron mobility transistors (HEMTs) with different backsides via layouts are presented. AlGaN/GaN HEMTs with outside backside via (OSV) and internal backside via (ISV) were processed with the same device geometry on the same wafer. HEMTs with ISV layout show a lower thermal resistance because of an extra via at the center of device. Comparisons of the device characteristics of HEMTs with OSV and ISV layouts including threshold voltage, on-resistance, and source resistance (extracted from DC measurements) and drain resistance, gate-source capacitance, gate-drain capacitance, and drain-source capacitance (extracted from RF measurements) are discussed at different temperatures. Moreover, pulsed measurements confirmed that the difference in drain current from DC measurement due to self-heating is less in the ISV layout.

Advanced HEMT Characteristics of Epitaxial Quality-Improved GaN by Using Patterned Sapphire

An efficient method to modify the defect density of a gallium nitride (GaN) epi-wafer is proposed in this study. A patterned sapphire substrate (PSS) was used here acting as the medium for defect adjustment. The characteristics of yielded samples were analyzed by Raman scattering and etching pitch density (EPD) methods, which did show the improved crystal quality of GaN. Following high electron mobility transistor (HEMT) application based on the yield sample was executed, and the performances of the devices did improve as well.

Dynamic Control of AlGaN/GaN HEMT Characteristics by Implementation of a p-GaN Body-Diode-Based Back-Gate

We report on the implementation of dynamic body-bias technique to improve the performance of AlGaN/GaN high electron mobility transistors (HEMTs) with the successful integration of body-diode. In this configuration, p-GaN body-diode-based back-gate control is used to shift the threshold voltage and dynamically modulate the ON/OFF characteristics of a normally-ON AlGaN/GaN HEMT. A fourth back-gate terminal is connected to the p-GaN layer to control the depletion width of the body-diode, which in turn modulates the 2-D electron gas (2DEG) density. A positive/negative shift in the threshold voltage is measured by increasing/decreasing the depletion width below the channel. A positive back-gate bias application in the ON-state is shown to increase the 2DEG current density resulting in higher ON-current. The application of a negative back-gate bias is shown to be effective in the positive shift of the threshold voltage, in reducing the 2DEG channel current and in increasing the OFF-state break-down voltage. We have experimentally demonstrated enhanced effect of body-diode-based back-gate control in shifting the threshold voltage of a normally-ON HEMT toward normally-OFF mode. The optimum back-gate voltage range which can be applied during both ON and OFF states has been experimentally determined.

Communication—Potential of the π-Gate InAs HEMTs for High-Speed and Low-Power Logic Applications

Composite channel (In0.65Ga0.35As/InAs/ In0.65Ga0.35As) high electron mobility transistors (HEMTs) with π-gate structure were investigated for high-speed and low-power logic applications. The conventional and tri-gate MESA HEMTs were compared with the π-gate device for evaluation. The π-gate device exhibited the best maximum transconductance value of 1584 mS/mm, on-state current of 332mA/mm, subthreshold swing (SS) of 78.1 mV/decade, and ION/IOFF ratio of 3 × 104 at VDS = 0.5 V at room temperature. These results indicated that the designed π-gate InAs devices improve the electrical characteristics of InAs HEMTs for high-speed and low-power logic applications.