Double-channel HEMT Research Articles

Suppressed gate leakage and enlarged gate over-drive window of E-mode p-GaN gate double channel HEMTs

A 600-V p-GaN gate double channel HEMT (DC-HEMT) is presented with a systematic investigation of the gate characteristics, including the leakage current, breakdown, and reliability under forward bias stress. It is found that the gate leakage of the DC-HEMT is substantially lower than that of the p-GaN single channel HEMT (SC-HEMT) owing to suppressed electron spillover that stems from hole storage in the quantum well upper channel. Consequently, the gate breakdown voltage of the DC-HEMT is improved to 14.7 V compared to 12.2 V of the SC-HEMT. Besides, the gate operating voltage margin of the DC-HEMT is expanded to 4.2 V compared to 3.3 V of the SC-HEMT according to the gate lifetime evaluation.

Improved DC and RF Characteristics of GaN-Based Double-Channel HEMTs by Ultra-Thin AlN Back Barrier Layer.

In order to improve the off-state and breakdown characteristics of double-channel GaN HEMTs, an ultra-thin barrier layer was chosen as the second barrier layer. The strongly polarized and ultra-thin AlN sub-barrier and the InAlN sub-barrier are great candidates. In this article, the two epitaxial structures, AlGaN/GaN/AlN/GaN (sub-AlN) HEMTs and AlGaN/GaN/InAlN/GaN (sub-InAlN) HEMTs, were compared to select a more suitable sub-barrier layer. Through TEM images of the InAlN barrier layer, the segregation of In components can be seen, which decreases the mobility of the second channel. Thus, the sub-AlN HEMTs have a higher output current density and transconductance than those of the sub-InAlN HEMTs. Because the high-quality AlN barrier layer shields the gate leakage current, a 294 V breakdown voltage was achieved by the sub-AlN HEMTs, which is higher than the 121 V of the sub-InAlN HEMTs. The current gain cut-off frequency (fT) and maximum oscillation frequency (fmax) of the sub-AlN HEMTs are higher than that of the sub-InAlN HEMTs from low to high bias voltage. The power-added efficiency (PAE) and output power density (Pout) of the sub-AlN HEMTs are 57% and 11.3 W/mm at 3.6 GHz and 50 V of drain voltage (Vd), respectively. For the sub-InAlN HEMTs, the PAE and Pout are 41.4% and 8.69 W/mm, because of the worse drain lag ratio. Thus, the Pout of the sub-AlN HEMTs is higher than that of the sub-InAlN HEMTs.

Deep insight of inter-channel coupling in AlGaN/GaN double channel HEMT and its application in C-ERB2 sensing

AlGaN/GaN Double Channel High Electron Mobility Transistors (DCHEMTs) have emerged as promising biosensors, leveraging the unique properties of inter-channel coupling. This paper investigates the influence of mole fraction variations in the AlGaN layer on inter-channel coupling and explores its implications for C-ERB2 biosensing. The study reveals the potential of inter-channel coupling to enhance sensitivity in biosensing applications, particularly for detecting C-ERB2, a crucial protein associated with various cancers. The device architecture, simulation models, electrostatics, and sensitivity analysis are comprehensively examined. The findings underscore the significance of inter-channel coupling in optimizing biosensor performance, offering valuable insights for the advancement of biosensing technologies.

Polarization Properties in GaN Double-Channel HEMTs at Mid-Infrared Frequencies

Polarization Properties in GaN Double-Channel HEMTs at Mid-Infrared Frequencies

On the double channel engineering of dual gate AlGaN/GaN HEMTs for heavy ion sensing applications

This work investigates the influence of Single Event Transient (SET) effect on Double Channel Dual Gate (DC-DG) AlGaN/GaN HEMT using TCAD simulations. Both Single Channel (SC) and Double Channel HEMT have been calibrated with reported experimental results and further extended by introducing a second gate in the structures to analyze its sensitivity towards heavy ion strike. The effective gate length has been optimized in such a way that the saturation currents and threshold voltage of dual gate devices is similar to that of the single gate devices. The DC-DG HEMT improves the heavy ion sensitivity, thus making it a more viable device for sensing application (mainly radiation). Different biases and gate materials have been used to observe the influence of SET on the DC-DG AlGaN/GaN HEMT. Further, the impact of the graded AlGaN barrier on the device current as well as on the sensitivity of the DC-DG HEMT towards SET is studied. To ascertain the performance of DC-DG HEMT for dosimeter applications, its sensitivity toward heavy ion impact in switched mode is monitored. Investigation reveals that the device current returns to its original order of magnitude after every ion impact, and therefore can be effectively used as a dosimeter.

Normally-OFF p-GaN Gate Double-Channel HEMT With Suppressed Hot-Electron-Induced Dynamic ON-Resistance Degradation

Hot electrons with high kinetic energy could be generated in the channel of GaN high-electron-mobility transistors (HEMTs) during hard switching operation. Those “lucky” hot electrons scattered to the vulnerable interface between the passivation and barrier layers could bombard the interface region and create new defects that would lead to degradation of the dynamic on-resistance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{ON}$ </tex-math></inline-formula> ) after long-term operations. In this work, we propose a solution to the hot-electron induced device degradation through channel engineering, i.e., deploying a double-channel structure in place of the conventional single-channel structure in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${p}$ </tex-math></inline-formula> -GaN gate HEMTs. It is revealed that hot electrons are mostly generated in the lower channel and thus the additional scattering interface can effectively deter the hot electrons from reaching the vulnerable surface. Dynamic <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{ON}$ </tex-math></inline-formula> degradation induced by long-term stresses at “semi-on” states is shown to be substantially suppressed in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${p}$ </tex-math></inline-formula> -GaN gate HEMT with the double-channel structure.

Investigation on the Influence of Ohmic Structure on Channel-to-Channel Coupling Effect in InAlN/GaN Double Channel HEMTs

In this paper, the impact of ohmic structure on channel-to-channel (C2C) coupling effect in InAlN/GaN double channel (DC) HEMTs is systematically analyzed and studied. For the un-recessed ohmic structure, the electrons in the upper channel can easily inject into the bottom channel due to the ultra-thin InAlN back barrier layer. Therefore, the maximum drain current and transconductance peak of the bottom channel significantly increase. For recessed ohmic structure, the reduced vertical electric field strength of the upper channel can effectively weaken the coupling effect between the two GaN channels. Benefiting from the suppressed vertical transport of electrons in the upper channel, higher drain current and transconductance of the upper channel are obtained in the recessed ohmic structure. In addition, the transmission electron microscope (TEM) microstructural analysis of the DC HEMTs with recessed ohmic structure was also performed. This shows that the recessed ohmic structure can modulate the electron transport mode in the InAlN/GaN DC HEMTs. The coupling effect of the two channels will play a major role in influencing the characteristics of current gain cutoff frequency (fT) / maximum power gain cutoff frequency (fmax) versus VGS and have a significant effect on large-signal characteristics, which is quite attractive for the fabrication of power microwave GaN-based HEMTs with wide gate swing.

Design and Investigation of Recessed-T-Gate Double Channel HEMT with InGaN Back Barrier for Enhanced Performance

Design and Investigation of Recessed-T-Gate Double Channel HEMT with InGaN Back Barrier for Enhanced Performance

TCAD Based Investigation of Single Event Transient Effect in Double Channel AlGaN/GaN HEMT

In this paper, investigation of Double Channel (DC) AlGaN/GaN HEMT has been presented using extensive TCAD simulation under the influence of Single Event Transient (SET) effect. Various models used to emulate Single Channel (SC) and DC HEMT in the TCAD are calibrated with the help of previously reported work. In order to present clear insight into the device behaviour, thermal model has also been included during device simulation. Presented results show that the generation of electron-hole pair due to heavy ion beam is significantly higher in DC HEMT during both OFF and ON state conditions. Ion beam having different Linear Energy Transfer (LET) and different position of Ion strike along with penetration depth has been used for investigating the SET effect on DC and SC AlGaN/GaN HEMT. The suitability of different metal gate work-function for heavy Ion detection has also been performed using both devices and DC HEMT (0.115 A/mm) demonstrated superior \bigtriangleup I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> DMAX</sub> as compared to SC HEMT (0.049 A/mm). The presence of a second channel in Double Channel (DC) HEMT leads to a device more sensitive towards the Single Event Transients (SET) Effect, thus, a more suitable candidate for radiation dosimeter as compared to Single Channel (SC) HEMT.

Applicability of Field Plate in Double Channel GaN HEMT for Radio-Frequency and Power-Electronic Applications

In the present communication, for the first time, applicability of Field Plate (FP) for Double Channel (DC) AlGaN/GaNHEMT is demonstrated. Impact of design space parameters such as field plate length (LFP) and Silicon Nitride thickness (tSiN) on breakdown voltage of DC HEMT is investigated and benchmarked with Single Channel (SC) HEMT. The investigation is carried out using ATLAS Technological Computer Aided Design (TCAD) Simulation tool, which is an efficient method in terms of time and cost to analyze and understand DC HEMT prior to the fabrication. The simulation shows new findings that breakdown voltage of DC device exhibited a large deviation with that of SC device. The breakdown voltage deviation is well corroborated through electric field, impact ionization and off-state leakage analysis. The electric field analysis has shown optimal value of LFP and tSiN for DC HEMT. It is also observed that tSiN for DC-HEMT should be lower than that of SC-HEMT. In this paper, the off-state leakage, electron-depletion and impact ionization are the first-hand observations for benchmarking DC device with SC device. Furthermore, it is found that DC device yield higher cut-off frequency and device linearity than that of SC device, which is highly desirable for Radio-Frequency (RF) and linear amplifiers. Thus, the observation presented in this paper assist device technologist to enhance the performance of DC device further and foundries to optimize the FP for DC device.

A Rigorous Investigation of Electrostatic and Transport Phenomena of GaN Double-Channel HEMT

This paper presents a comprehensive investigation of electrostatics and transport characterization of GaN double-channel (DC) MOS-HEMT. Upon derivation of a polynomial analytical expression establishing a relationship between the Fermi level and the 2-D electron gas density (2DEG), a relationship between the sheet carrier density and applied gate voltage has been obtained. To confirm the validity of the model in both subthreshold and strong inversion regions, the charge density profile and capacitance–voltage profile have been attained from self-consistent simulation incorporating the quantum mechanical effect. The impact of GaN channel thickness on the conduction band profile as well as charge density profile has also been investigated. A 2-D analytical model for current–voltage characteristics of GaN-DC-MOS-HEMT has been developed for the first time. Assuming velocity saturation of electrons in 2DEG, the effects of spontaneous and piezoelectric polarization at the heterointerface, field dependent mobility, and the parasitic source and drain resistance have been taken into account in evolution of this model. The ON-resistance extracted from the analytical model was found to be 7.1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega \cdot $ </tex-math></inline-formula> mm, which is in close proximity with experimental results. A steep subthreshold swing of 79 mV/dec was determined from the current–voltage characteristics with an ON– OFF drain current ratio of the order of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> , which holds the promising application for enhancement mode operation with minimal leakage current. For corroboration, the derived results were compared with experimental data acquired from the literature, thereby enhancing the reliability of this model.

The Study of Self-Heating and Hot-Electron Effects for AlGaN/GaN Double-Channel HEMTs

The direct current characteristics of AlGaN/GaN double-channel HEMTs (DC-HEMTs) are investigated by using 2-D numerical simulations. The output characteristics have been predicted with the drift-diffusion, thermodynamic, hydrodynamic, and hot-electron models, respectively. The prediction by the hydrodynamic model is in good agreement with the experiment. It is demonstrated that the hot-electron effect makes a negligible contribution to the negative differential conductance (NDC) of an AlGaN/GaN DC-HEMT; instead, the NDC effect is caused by the self-heating effect. The transfer and transconductance characteristics of an AlGaN/GaN DC-HEMT are also discussed in detail. Finally, a new In0.18Al0.82N /GaN/AlGaN/GaN DC-HEMT structure is proposed for optimizing AlGaN/GaN DC-HEMTs.

AlGaN/GaN double-channel HEMT

The fabrication of AlGaN/GaN double-channel high electron mobility transistors on sapphire substrates is reported. Two carrier channels are formed in an AlGaN/GaN/AlGaN/GaN multilayer structure. The DC performance of the resulting double-channel HEMT shows a wider high transconductance region compared with single-channel HEMT. Simulations provide an explanation for the influence of the double-channel on the high transconductance region. The buffer trap is suggested to be related to the wide region of high transconductance. The RF characteristics are also studied.

AlGaN-GaN Double-Channel HEMTs

We present the design, fabrication, and characterization of AlGaN-GaN double-channel HEMTs. Two carrier channels are formed in an AlGaN-GaN-AlGaN-GaN multilayer structure grown on a sapphire substrate. Polarization field in the lower AlGaN layer fosters formation of a second carrier channel at the lower AlGaN-GaN interface, without creating any parasitic conduction path in the AlGaN barrier layer. Unambiguous double-channel behaviors are observed at both dc and RF. Bias dependent RF small-signal characterization and parameter extraction were performed. Gain compression at a high current level was attributed to electron velocity degradation induced by interface scattering. Dynamic IV measurement was carried out to analyze large-signal behaviors of the double-channel high-electron mobility transistors. It was found that current collapse mainly occurs in the channel closer to device surface, while the lower channel suffers minimal current collapse, suggesting that trapping/detrapping of surface states is mainly responsible for current collapse. This argument is supported by RF large-signal measurement results.

Theoretical analysis of HEMT breakdown dependence on device design parameters

A two-dimensional numerical analysis is presented to investigate the breakdown characteristics of single- and double-channel AlGaAs/GaAs HEMTs. The influence of the doped layer thickness and the thickness of an undoped i-layer under the gate is analyzed. Impact ionization is considered to be the dominant breakdown mechanism. All simulations reveal the existence of a high electric field region near the gate contact. Breakdown occurs in the gate-drain region and the (breakdown) path which maximizes the ionization integral is entirely in the AlGaAs layer. For increased donor layer thickness, single-channel devices biased near pinchoff have gate-drain breakdown voltages varying from 8 to 14 V with corresponding peak electric field values in the range of 8.2*10/sup 5/ to 2.4*10/sup 6/ V/cm. The breakdown voltage increases with increasing gate bias mod V /sub gs/ mod due to a screening effect of transverse from longitudinal electric field. Double-channel HEMTs have slightly higher breakdown than single-channel, especially near pinchoff and for thin donor layers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Passivation of GaAs FET's with PECVD silicon nitride films of different stress states

The passivation of GaAs MESFETs with plasma-enhanced chemical-vapor-deposited (PECVD) silicon nitride films of both compressive and tensile stress is reported. Elastic stresses included in GaAs following nitride passivation can produce piezoelectric charge density, which results in a shift of MESFET characteristics. The shift of MESFET parameters due to passivation was found to be dependent on gate orientation. The experiments show that nitride of tensile stress is preferable for MESFETS with (011-bar) oriented gates. The shifts in V/sub TH/,I/sub DSS/, and G/sub M/ of the devices before and after nitride passivation are less than 5% if the nitride of appropriate stress states are used for passivation. The breakdown voltage of the MESFETs after nitride deposition was also studied. It is found that the process with higher hydrogen incorporation tends to reduce the surface oxide and increase the breakdown voltage after nitride deposition. In addition, the passivation of double-channel HEMTs is reported for the first time. >