Metal-oxide-semiconductor High Electron Mobility Transistors Research Articles

GaN-HEMT Performance Enhancement

In this work, a simulation analysis and calibration are carried out to improve the performance of AlGaN/GaN- MOSHEMTs (Metal-Oxide Semiconductor High Electron Mobility Transistors). The effect of the AlGaN layer thickness, gate length, Al mole fraction, and the interface traps on the electrical performance of the device has been presented. Device simulations have been done using Sentaurus technology computer-aided design (TCAD). The simulations and analysis show better drain current, transconductance, and cut-off frequency performance. The maximum cut-off frequency shown by the proposed HEMT device is 45.7 GHz at 100-nm gate length. Good transcoductance has been obtained by scaling down the gate length of the device, which is ascribed to the present two-dimensional electron gas (2DEG) density that supports upgrading the output current. Higher drain current is achieved without using acceptor-like traps in the Al2O3/AlGaN interface. Results show that the Al2O3/AlGaN/GaN-based MOSHEMT is a promising device for high-frequency and power electronic applications.

Sensitivity estimation of biosensor in a tapered cavity MOSHEMT

The present research provides a comprehensive investigation of the structural modification at the cavity under the gate (CUG) on the metal oxide semiconductor high electron mobility transistor (MOSHEMT)-based biosensor by projecting its basic figures of merit (FOMs). The effect of a tapering dielectric on the sensitivity of the biosensor has not been extensively investigated in many research efforts. Therefore, to account for the larger binding surface, the current study considers a wide range of permittivity of the biomolecules from 1 to 10, using the dielectric modulation technique in the tapered cavity. Various cavities are analysed to enhance the sensitivity. The findings indicate that the presence of biomolecules causes a considerable fluctuation in the drain current, threshold voltage, on-current, off-current, channel potential, and oxide capacitance. It has also been estimated how various fill percentages and charged and neutral biomolecules affect the device’s sensitivity. The tapered dielectric MOSHEMT offered an on-current sensitivity and threshold voltage sensitivity of 1.25 and 0.889 for neutral biomolecule (k = 8) and 0.562 and 2.23 for positively charged biomolecule respectively. Thus, tapering of the oxide does offer better sensitivities that can be exploited for biosensing applications.

Numerical study of T-Gate AlGaN/AlInGaN/GaN MOSHEMT with Single and Double Barrier for THz Frequency Applications

This paper presents a comprehensive investigation into the DC analog and AC microwave performance of a state-of-the-art T-gate double barrier AlGaN/AlInGaN/GaN MOSHEMT (Metal Oxide Semiconductor High Electron Mobility Transistor) implemented on a 4H-SiC substrate. The study involves meticulous numerical simulations and an extensive comparison with a single barrier design, utilizing the TCAD-Silvaco software. The observed disparity in performance can be attributed to the utilization of double barrier technology, which enhances electron confinement and current density by augmenting the polarization-induced charge during high-frequency operations. Remarkably, when compared to the single barrier design, the double barrier MOSHEMT exhibits a notable 15% increase in drain current, a 5% increase in transconductance, and an elevated breakdown voltage (VBR) of 140 V in E-mode operation. Furthermore, the radio frequency analysis of the double barrier device showcases exceptional performance, setting new records with a maximum oscillation frequency (fmax) of 1.148 THz and a gain cutoff frequency (ft) of 891 GHz. These impressive results obtained through deck-simulation affirm the immense potential of the proposed double barrier AlGaN/AlInGaN/GaN MOSHEMT for future applications in high-power and terahertz frequency domains.

Insight into the suppression mechanism of bulk traps in Al2O3 gate dielectric and its effect on threshold voltage instability in Al2O3/AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors

Bulk trapping and its effects on threshold voltage hysteresis (ΔVTH) in Al2O3/AlGaN/GaN metal–oxide-semiconductor high electron mobility transistors (MOS-HEMTs) have been identified by a combination of isothermal capacitance transient spectroscopy (ITS) and X-ray photoelectron spectroscopy (XPS). A post deposition annealing (PDA) at 500 °C in O2 ambient is confirmed to be an effective way to reduce the bulk traps in an atomic layer deposited (ALD)-Al2O3 film as it contributes to the suppressed ΔVTH in Al2O3/AlGaN/GaN MOS-HEMTs. The interface and bulk trapping behavior that account for ΔVTH, have been distinguished by ITS. It is revealed that continual charging of bulk traps in the Al2O3 gate dielectric occurred once the gate bias of the MOS-HEMTs is applied exceeding +3 V, which leads to the degraded ΔVTH as well as subthreshold slopes in transfer characterization. Such bulk traps probably stem from the Al-O-H component in the as-deposited Al2O3 layers, as detected by XPS. Energy band simulation further illustrates the capture process of the bulk traps, verifying the physical relationship between bulk-trapping and ΔVTH in GaN-based MOS-HEMTs.

AlGaN/GaN Metal Oxide Semiconductor High-Electron Mobility Transistors with Annealed TiO2 as Passivation and Dielectric Layers.

This paper reports on improved AlGaN/GaN metal oxide semiconductor high-electron mobility transistors (MOS-HEMTs). TiO2 is used to form the dielectric and passivation layers. The TiO2 film is characterized using X-ray photoemission spectroscopy (XPS), Raman spectroscopy, and transmission electron microscopy (TEM). The quality of the gate oxide is improved by annealing at 300 °C in N2. Experimental results indicate that the annealed MOS structure effectively reduces the gate leakage current. The high performance of the annealed MOS-HEMTs and their stable operation at elevated temperatures up to 450 K is demonstrated. Furthermore, annealing improves their output power characteristics.

Impact of InGaN notch on sensitivity in dielectric modulated dual channel GaN MOSHEMT for label-free biosensing

The effect of InGaN notch on sensitivity and Dielectric Modulated (DM) Double Heterojunction (DH) dual channel AlGaN/GaN/InGaN/GaN MOSHEMT (Metal Oxide Semiconductor High Electron Mobility Transistor) for detecting the label-free biomolecules has been investigated in this paper. Biomolecules can be inserted into the nanocavity formed by etching the insulating layer under the gate electrode. The insulator (Al2O3) as a dielectric improves the drive current and device sensitivity because of low leakage and high scalability. In this proposed structure, the presence of InGaN notch increases the carrier confinement in the channel, thereby improving the device sensitivity. The device is simulated using Sentaurus TCAD, and the results show a significant increase in drain current (IDS), up to 335 mA/mm. The optimization of the device parameters exhibits a high sensitivity (∼74%), making it suitable for precise label-free biosensing.

Gate dielectric layer mitigated device degradation of AlGaN/GaN-based devices under proton irradiation

In this study, the simulations of AlGaN/GaN-based devices, including AlGaN/GaN high electron mobility transistor (HEMT), Al2O3 metal–oxide–semiconductor high electron mobility transistor (MOSHEMT), and SiNx metal–insulator–semiconductor high electron mobility transistor (MISHEMT), were studied to investigate the degradation mechanism after proton irradiation. The vacancies produced by proton irradiation, especially Ga vacancy (VGa), are found to be responsible for the device degradation by carrier removal and mobility degradation, which directly influence the saturation drain current and maximum transconductance of AlGaN/GaN-based devices. Furthermore, AlGaN/GaN HEMTs with gate dielectrics (Al2O3, SiNx) exhibit better irradiation resistance than traditional AlGaN/GaN HEMTs, which produce fewer vacancies at the channel after proton irradiation. Al2O3 MOSHEMTs also show better performance than SiNx MISHEMTs in resisting proton damage. Therefore, a high-quality dielectric layer is a key factor to improve the reliability of AlGaN/GaN-based devices after proton irradiation.

Dual gate AlGaN/GaN MOS-HEMT biosensor for electrical detection of biomolecules-analytical model

This paper proposes an analytical model for a dual gate AlGaN/GaN Metal oxide semiconductor-high-electron-mobility transistor (MOS-HEMT) biosensor for electrical detection of neutral species such as Biotin, Keratin, ChOx, and Zein. When only one subband is occupied and the AlGaN layer is assumed to have been fully ionized, the Fermi–Dirac statistic and 2D state density are used to produce a self-consistent calculation of the carrier density in the quantum well at the interface. It is done by analyzing the impact of biomolecule concentration by inserting a biomolecule of appropriate dielectric permittivity in the cavity area beneath the gate region. The impact of cavity length has been analyzed on the sensor’s performance. The proposed device significantly changes the channel potential, transconductance, drain current, and threshold voltage. Dual gate structures offer superior resistance to short channel effects. Due to enhanced transport characteristics, high carrier mobility, drain current, and a variety of other factors, double gate MOS HEMT outperforms single-gate MOS HEMT. The maximal transconductance, drain on sensitivity, and the maximal drain current that has been attained in this work is 0.017 s, 0.22 and 0.129 mA, respectively, for biomolecule concentration, N b = 3 × 1012. Among all the biomolecules used in this study, Keratin has achieved the maximum shift in threshold voltage and transconductance of 0.4 V and 0.016 s. The increase in current for Keratin, Biotin, Zein, and ChOx is 0.67%, 78%, 17%, and 42%, respectively, from single to dual gate AlGaN/GaN MOS-HEMT. SiO2, Al2O3, and HfO2 oxides have been compared by filling them in the left side of the cavity. Dual gate AlGaN/GaN MOS-HEMT biosensor presents an opportunity to develop robust, low-cost, specific detection and analysis of neutral biomolecule. The analytical model provides good results for drain current according to the comparison of simulation and analytical model findings.

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.

Improved RF-DC characteristics and reduced gate leakage in GaN MOS-HEMTs using thermally grown Nb2O5 gate dielectric

This work demonstrates the improvement in DC and RF characteristics and a reduction in the gate leakage current for thermally grown Nb2O5 as a gate dielectric in AlGaN/GaN metal–oxide–semiconductor high electron-mobility transistors (MOS-HEMTs). The MOS-HEMTs with an amorphous 10 nm thick Nb2O5 as the gate dielectric show a reduced gate leakage current of 10−9 A mm−1. Nb2O5 thin film creates a tensile strain in the AlGaN layer, enhancing the density of two-dimension electron gas (2-DEG). The performance of the device also improves in terms of saturation drain current, peak transconductance, subthreshold swing, and unity current gain frequency. An increase in the source-to-drain ON/OFF current ratio to 108 and a significant reduction in the subthreshold leakage current by at least two orders of magnitude are measured compared to the control HEMTs.

Influence of the Cl2 etching on the Al2O3/GaN metal–oxide–semiconductor interface

Controlling the plasma etching step involved in metal-oxide-semiconductor high-electron-mobility-transistor (MOSHEMT) GaN fabrication is essential for device performance and reliability. In particular, understanding the impact of GaN etching conditions on dielectric/GaN interface chemical properties is critically important. In this work, we investigate the impact of the carrier wafers (Si, photoresist, SiO2, and Si3N4) used during the etching of GaN in chlorine plasma on the electrical behavior of Al2O3/n-GaN metal–oxide–semiconductor (MOS) capacitors. X-ray Photoelectron spectroscopy (XPS) analyses show that the Al2O3/GaN interface layer contains contaminants from the etching process after the Al2O3 deposition. Their chemical nature depends on the plasma chemistry used as well as the chemical nature of the carrier wafer. Typically, Cl and C are trapped at the interface for all substrates. In the particular case of Si carrier wafer, a significant amount of SiOx is present at the Al2O3/GaN interface. The capacitance–voltage (C–V) characteristics of the MOS capacitors indicate that the presence of Si residues at the interface shifts the flat band voltage to negative values, while the presence of Cl or C at the interface increases the hysteresis. We demonstrate that introducing an in situ plasma cleaning treatment based on N2/H2 gas, before the atomic layer deposition, allows the removal of most of the residues except silicon and suppresses the hysteresis.

Improved Electrical Characteristics of AlGaN/GaN High-Electron-Mobility Transistor with Al2O3/ZrO2 Stacked Gate Dielectrics.

A metal-oxide-semiconductor high-electron-mobility transistor (MOS-HEMT) is proposed based on using a Al2O3/ZrO2 stacked layer on conventional AlGaN/GaN HEMT to suppress the gate leakage current, decrease flicker noise, increase high-frequency performance, improve power performance, and enhance the stability after thermal stress or time stress. The MOS-HEMT has a maximum drain current density of 847 mA/mm and peak transconductance of 181 mS/mm. The corresponding subthreshold swing and on/off ratio are 95 mV/dec and 3.3 × 107. The gate leakage current can be reduced by three orders of magnitude due to the Al2O3/ZrO2 stacked layer, which also contributes to the lower flicker noise. The temperature-dependent degradation of drain current density is 26%, which is smaller than the 47% of reference HEMT. The variation of subthreshold characteristics caused by thermal or time stress is smaller than that of the reference case, showing the proposed Al2O3/ZrO2 stacked gate dielectrics are reliable for device applications.

AlGaN/AlN/GaN Metal-Oxide-Semiconductor High-Electron Mobility Transistor with Annealed Al2O3 Gate Dielectric

An AlGaN/AlN/GaN metal-oxide-semiconductor high-electron mobility transistors (MOS-HEMT) with an Al2O3 insulator is studied. The post-deposition annealing (PDA) of Al2O3 is conducted. The effects of PDA in an N2 atmosphere on the performance of the MOS-HEMTs are studied. Experimental results demonstrate that the trap density in the Al2O3 MOS diode is significantly decreased by annealing. Adding annealed Al2O3 as a surface passivation and a gate oxide layer on HEMTs reduces gate leakage currents, increases the two-terminal reverse breakdown voltage, and improves the high-frequency performance of the HEMTs.

Analytical Modeling of MgZnO/ZnO MOSHEMT Based Biosensor for Biomolecule Detection

In recent development, the High Electron Mobility Transistor (HEMT) technology was used for biosensor applications. In this contribution, an analytical model of MgZnO/ZnO MOSHEMT (Metal Oxide Semiconductor HEMT) was reported. For the first time, a nanogap cavity-based biosensor aimed at detecting various biomolecules, such as uricase, streptavidin, ChOx, and proteins, was designed. The developed analytical model was used to calculate the two-dimensional electron gas (2DEG) density, device capacitance, drain current (ID), output conductance (gd), and transconductance (gm) by using the dielectric modulation approach. MOSHEMTs used dielectric modulation, with the nanogap cavity considered under the gate region. The effective capacitance in the cavity region was obtained by using dielectric modulation. Hence, the nanogap cavity acts as a sensing area for the immobilisation of target biomolecules. The sensitivity of the device was analysed by observing the strong changes in drain current with the addition of different biomolecules in the nanogap cavity region. The proposed MgZnO/ZnO MOSHEMT biosensor exhibits a quick response to biomolecule changes since its drain-on-sensitivity (SIon) is comparatively higher than that of other semiconductor-based biosensors. The obtained analytical model results were verified by a comparison with other works available in the literature, and they showed good agreement with our results.

Performance Comparison of Lattice-Matched AlInN/GaN/AlGaN/GaN Double-Channel Metal–Oxide–Semiconductor High-Electron Mobility Transistors with Planar Channel and Multiple-Mesa-Fin-Channel Array

In this work, Al0.83In0.17N/GaN/Al0.18Ga0.82N/GaN epitaxial layers used for the fabrication of double-channel metal–oxide–semiconductor high-electron mobility transistors (MOSHEMTs) were grown on silicon substrates using a metalorganic chemical vapor deposition system (MOCVD). A sheet electron density of 1.11 × 1013 cm−2 and an electron mobility of 1770 cm2/V-s were obtained. Using a vapor cooling condensation system to deposit high insulating 30-nm-thick Ga2O3 film as a gate oxide layer, double-hump transconductance behaviors with associated double-hump maximum extrinsic transconductances (gmmax) of 89.8 and 100.1 mS/mm were obtained in the double-channel planar MOSHEMTs. However, the double-channel devices with multiple-mesa-fin-channel array with a gmmax of 148.9 mS/mm exhibited single-hump transconductance behaviors owing to the better gate control capability. Moreover, the extrinsic unit gain cutoff frequency and maximum oscillation frequency of the devices with planar channel and multiple-mesa-fin-channel array were 5.7 GHz and 10.5 GHz, and 6.5 GHz and 12.6 GHz, respectively. Hooge’s coefficients of 7.50 × 10−5 and 6.25 × 10−6 were obtained for the devices with planar channel and multiple-mesa-fin-channel array operating at a frequency of 10 Hz, drain–source voltage of 1 V, and gate–source voltage of 5 V, respectively.

Influence of back barrier layer thickness on device performance of AlGaN/GaN MOS-HEMT

In this work, we have performed the influence of back barrier layer thickness variation on AlGaN/GaN Metal Oxide Semiconductor High Electron Mobility Transistor (MOS-HEMT) device with 0.5 µm Schottky gate length. The AlGaN back barrier layer presented increases the conduction band with respect to GaN channel layer so that more no of electron confinement into the GaN channel layer and improve the high-frequency performance. The effect of the back-barrier layer thickness is performed by using 2-D TCAD Atlas Silvaco numerical simulation tool by taking Hydrodynamic mobility model. Due to a large amount of two-dimensional electron gas (2-DEG) density at the AlGaN/GaN heterointerface of the MOS-HEMT device higher drain current density is obtained. The 2-D simulation is carried out with a variation of back barrier layer thickness for various device parameter such as transfer characteristics (Id-Vg), drain current with a drain voltage (Id-Vd), transconductance (gm), drain induced barrier lowering (DIBL), conduction band energy and electron concentration into the channel. In this simulation, we have also performed the RF performance like a gate to source capacitance (Cgs) and current gain cut-off frequency of AlGaN/GaN MOS-HEMT device. The results obtained by variation of AlGaN back barrier layer thickness can be a better solution in future analog and RF device application. Copyright © 2018 VBRI Press.

Investigation of Multi-Mesa-Channel-Structured AlGaN/GaN MOSHEMTs with SiO2 Gate Oxide Layer

In this study, an electron-beam lithography system was employed to pattern 80-nm-wide and 980-nm-spaced multi-mesa-channel for fabricating AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors (MOSHEMTs). Since the structure of multi-mesa-channel could enhance gate control capabilities and reduce the self-heating effect in the channel, the performance of the MOSHEMTs could be obviously improved. The direct current performance metrics of the multi-mesa-channel-structured MOSHEMTs, such as a saturation drain-source current of 929 mA/mm, maximum extrinsic transconductance of 223 mS/mm, and on-resistance of 2.1 Ω-mm, were much better than those of the planar-structured MOSHEMTs. Moreover, the threshold voltage of the multi-mesa-channel-structured MOSHEMTs shifted toward positive voltage from −2.6 to −0.6 V, which was attributed to the better gate control capability. Moreover, the multi-mesa-channel-structured MOSHEMTs also had superior high-frequency and low-frequency noise performance. A low Hooge’s coefficient of 1.17 × 10−6 was obtained.

Modified Small Signal Circuit of AlGaN/GaN MOS-HEMTs Using Rational Functions

Conventional lumped small signal circuit (SSC) models of AlGaN/GaN metal oxide semiconductor high electron mobility transistors (MOS-HEMTs) are derived from the low frequency portion of the experimentally measured Y-parameters. Consequently, these models cannot faithfully capture the high frequency behavior of the device. In this work, modified SSC models of AlGaN/GaN MOS-HEMTs are developed by fitting the entire broadband measured Y-parameters of the device with rational functions. These rational functions are then physically realized using additional passive circuit elements added to the conventional SSC model. The accuracy of the proposed SSC models can be improved by increasing the order of the rational functions. The proposed models are demonstrably more accurate than the conventional SSC models in estimating the higher order poles and zeroes present in the experimentally measured Y-parameters of AlGaN/GaN MOS-HEMTs.

Low Subthreshold Slope AlGaN/GaN MOS-HEMT with Spike-Annealed HfO2 Gate Dielectric.

AlGaN/GaN metal-oxide semiconductor high electron mobility transistors (MOS-HEMTs) with undoped ferroelectric HfO2 have been investigated. Annealing is often a critical step for improving the quality of as-deposited amorphous gate oxides. Thermal treatment of HfO2 gate dielectric, however, is known to degrade the oxide/nitride interface due to the formation of Ga-containing oxide. In this work, the undoped HfO2 gate dielectric was spike-annealed at 600 °C after the film was deposited by atomic layer deposition to improve the ferroelectricity without degrading the interface. As a result, the subthreshold slope of AlGaN/GaN MOS-HEMTs close to 60 mV/dec and on/off ratio>109 were achieved. These results suggest optimizing the HfO2/nitride interface can be a critical step towards a low-loss high-power switching device.

Adoption of the Wet Surface Treatment Technique for the Improvement of Device Performance of Enhancement-Mode AlGaN/GaN MOSHEMTs for Millimeter-Wave Applications.

In this work, a low-power plasma oxidation surface treatment followed by Al2O3 gate dielectric deposition technique is adopted to improve device performance of the enhancement-mode (E-mode) AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors (MOSHEMTs) intended for applications at millimeter-wave frequencies. The fabricated device exhibited a threshold voltage (Vth) of 0.13 V and a maximum transconductance (gm) of 484 (mS/mm). At 38 GHz, an output power density of 3.22 W/mm with a power-added efficiency (PAE) of 34.83% were achieved. Such superior performance was mainly attributed to the high-quality Al2O3 layer with a smooth surface which also suppressed the current collapse phenomenon.