Metal Oxide Semiconductor High Electron Mobility 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.

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.

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.

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.

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.

Influence of Graded AlGaN sub-channel over the DC and Breakdown characteristics of a T-gated AlGaN/GaN/AlInN MOS-HEMT

The impact of graded Al0.05Ga0.95N sub-channel over the DC characteristics of AlGaN/GaN/AlInN Metal Oxide Semiconductor-High Electron Mobility Transistor (MOS-HEMT) has been investigated here. By placing a field plate over the gate region and forming a T-gated structure, the breakdown characteristics are examined using Sentaurus Technology Computer-Aided Design (TCAD) simulation tool. An analytical study is carried out into the evaluation of various device parameters like drain current, transconductance and threshold voltage. RF parameters like cut-off frequency and gain has also been examined. Various physical models such as hydrodynamic, thermodynamic, piezoelectric polarization, impact ionization models are considered. HfO2 as an oxide layer directly influences the charge confinement near the Two-Dimensional Electron Gas (2DEG), thereby causing a positive shift in the threshold voltage of the device. T-gated formation of the gate helped in enhancing the breakdown voltage of the device to nearly 750 V. A maximum current drive of 1.79 A/mm mm was obtained for the proposed device, nearly 24% improvement from the conventional Composite-channel (CC) HEMT. The current outcomes and the produced frequency characteristics determines the linearity enhancement occurred in the device, caused due to the graded AlGaN sub-channel below the GaN channel layer. The trade-off between specific on-resistance and breakdown voltage is well preserved by employing a T-gated structure with low normal gate length. The outcomes prove the device to be a prime contender for high power switching as well as large signal applications.

Observations regarding deep-level states causing p-type doping in AlTiO gate and positive threshold voltage shift in AlGaN/GaN high electron mobility transistors

Application of ternary oxides has emerged as a potential enabler to achieve enhancement mode (normally-OFF) operation in AlGaN/GaN high electron mobility transistors (HEMTs). However, it is not well understood what leads to the 2-Dimensional Electron Gas depletion or positive threshold voltage shift by the integration of these oxides in the gate stack. In this work, an electro-optical experiment-based method is used to probe the underlying mechanism. For experiments, AlGaN/GaN metal–oxide–semiconductor high electron mobility transistors with gate stack consisting of AlTiO (ternary p-type oxide), Al2O3, TiO2 (undoped binary oxides), and NiO (conventional p-type oxide) are used. Optical exposure with wavelengths falling in the UV regime (365 nm) was found to induce a negative threshold voltage shift in AlTiO based devices. Experimentation on different GaN buffer stacks, different gate oxides, and selective UV exposure only to the gate region established the phenomenon to be governed by properties of the ternary oxide. This was further confirmed by the fact that the negative threshold voltage shift with UV exposure was proportional to the positive shift achieved as a function of Al% in AlTiO. The negative shift was found to be due to de-ionization of deep-level negative states in AlTiO, which resulted from the presence of Al at Ti sites ([Al]Ti′). These negatively ionized deep-level states at room temperature result in p-type doping of the oxide, leading to the positive threshold voltage shift in AlTiO gate based HEMTs when compared with HEMTs with Al2O3 or TiO2 as gate oxide.

Degradation of gate-recessed MOS-HEMTs and conventional HEMTs under DC electrical stress* *Project supported by the Laboratory Open Fund of Beijing Smart-chip Microelectronics Technology Co., Ltd and the National Natural Science Foundation of China (Grant No. 11690042), the Science Challenge Project, China (Grant Nos. TZ2018004 and 12035019), and the National Major Scientific Research Instrument Projects, China (Grant No. 61727804).

The performance degradation of gate-recessed metal–oxide–semiconductor high electron mobility transistor (MOS-HEMT) is compared with that of conventional high electron mobility transistor (HEMT) under direct current (DC) stress, and the degradation mechanism is studied. Under the channel hot electron injection stress, the degradation of gate-recessed MOS-HEMT is more serious than that of conventional HEMT devices due to the combined effect of traps in the barrier layer, and that under the gate dielectric of the device. The threshold voltage of conventional HEMT shows a reduction under the gate electron injection stress, which is caused by the barrier layer traps trapping the injected electrons and releasing them into the channel. However, because of defects under gate dielectrics which can trap the electrons injected from gate and deplete part of the channel, the threshold voltage of gate-recessed MOS-HEMT first increases and then decreases as the conventional HEMT. The saturation phenomenon of threshold voltage degradation under high field stress verifies the existence of threshold voltage reduction effect caused by gate electron injection.

Combined Implications of UV/O3 Interface Modulation with HfSiOX Surface Passivation on AlGaN/AlN/GaN MOS-HEMT

Surface passivation is critically important to improve the current collapse and the overall device performance in metal-oxide semiconductor high-electron mobility transistors (MOS-HEMTs) and, thus, their reliability. In this paper, we demonstrate the surface passivation effects in AlGaN/AlN/GaN-based MOS-HEMTs using ultraviolet-ozone (UV/O3) plasma treatment prior to SiO2 -gate dielectric deposition. X-ray photoelectron spectroscopy (XPS) was used to verify the improved passivation of the GaN surface. The threshold voltage (VTH) of the MOS-HEMT was shifted towards positive due to the band bending at the SiO2/GaN interface by UV/O3 surface treatment. In addition, the device performance, especially the current collapse, hysteresis, and 1/f characteristics, was further significantly improved with an additional 15 nm thick hafnium silicate (HfSiOX) passivation layer after the gate metallization. Due to combined effects of the UV/O3 plasma treatment and HfSiOX surface passivation, the magnitude of the interface trap density was effectively reduced, which further improved the current collapse significantly in SiO2-MOS-HEMT to 0.6% from 10%. The UV/O3-surface-modified, HfSiOX-passivated MOS-HEMT exhibited a decent performance, with IDMAX of 655 mA/mm, GMMAX of 116 mS/mm, higher ION/IOFF ratio of approximately 107, and subthreshold swing of 85 mV/dec with significantly reduced gate leakage current (IG) of 9.1 ×10−10 A/mm.

Impact of AlInN Back-Barrier Over AlGaN/GaN MOS-HEMT With HfO₂ Dielectric Using Cubic Spline Interpolation Technique

The dc characteristics of AlGaN/gallium nitride (GaN) metal–oxide–semiconductor-high electron mobility transistor (MOS-HEMT) with an AlInN back-barrier layer has been studied here. An analytical model is proposed for evaluating the charge density ( $\sigma _{{\mathrm {tot}}}$ ), carrier concentration ( ${n}_{{\mathrm {S}}}$ ), drain current ( ${I}_{{\mathrm {D}}}$ ), and transconductance ( ${g}_{{\mathrm {m}}}$ ) of the device by incorporating Hafnium oxide (HfO2) as a high- ${k}$ dielectric layer. The charges created between the oxide and the AlGaN barrier layer influence the enhancement of carrier concentration of up to $6.2\times 10 ^{13}$ cm $^{-2}$ , at the two-dimensional electron gas (2DEG). The AlInN back-barrier increases the conduction band (CB) level of the GaN buffer and eliminates the confinement problems near the channel. By deriving the mathematical dependence of these parameters, this device demonstrated a positive threshold shift and a high current drive of 880 mA/mm. Cubic spline interpolation (CSI) technique is employed here to model the parameters in a more precise manner. The outcomes are evidence that the device could be a potential solution for high power switching as well as microwave applications.

An Extraction Method for the Interface Acceptor Distribution of GaN MOS-HEMT

This article presents a method for extracting the interface acceptor distribution of GaN metal–oxide–semiconductor high electron mobility transistor (MOS-HEMT) using a compact 2-dimensional electron gas model. The presented method is capable of self-consistently calculating the Fermi energy and the density of the ionized interface acceptor ( ${n}_{{\text {it},\text {A}}}$ ). Through the presented method, the density of states (DoS) of the interface acceptor ( ${D}_{{\text {it},\text {A}}}$ ) and ${n}_{{\text {it},\text {A}}}$ are obtained. Especially, the DoS of the interface acceptor distributed close to the conductband is also obtained. The calculated results are well supported by the results from the ac conductance method and the subthreshold swing (SS)-based method, thus verifying the correctness of the presented method.

Impact of Fin Width on Tri-Gate GaN MOSHEMTs

In this paper, we present a detailed investigation of the impact of fin width ( ${w}_{\text {fin}}$ ) on tri-gate AlGaN/GaN metal–oxide–semiconductor high electron mobility transistors (MOSHEMTs). As ${w}_{\text {fin}}$ is reduced, the threshold voltage ( ${V}_{\text {TH}}$ ) increases, which is due to the enhanced gate control (especially for ${w}_{\text {fin}} nm) thanks to the 3-D geometry of the tri-gate, and the reduced carrier concentration ( ${N}_{\text {s}}$ ) caused by a more pronounced strain relaxation and sidewall depletion, as explored using Hall and capacitance–voltage ( ${C}$ – ${V}$ ) measurements. Normally- OFF operation was achieved for ${w}_{\text {fin}}$ close to the sidewall depletion width ( ${w}_{\text {dep}}$ ) of 19.5 nm, since the fin is depleted from its two sidewalls. The impact of ${w}_{\text {fin}}$ on ON-resistance ( ${R} _{{{ {6{8} {\text {ON}}}}}}$ ) and current capability ( ${I} _{\text {D},\text {max}}$ ) was also investigated, along with the influence of the effective source injection, the trench conduction and the filling factor (FF) on these key characteristics. The degradation caused by the tri-gate fin etching could be fully recovered by increasing the FF. Finally, we show that the tri-gate can reduce gate capacitance ( ${C}_{\text {G}}$ ) and charge ( ${Q}_{\text {G}}$ ) in normally- ON MOSHEMTs, depending on the design of the tri-gate and the gate voltage ( ${V}_{\text {G}}$ ), leading to a smaller ${R}_{{{ {6{8} {\text {ON}}}}}} \cdot {Q}_{\text {G}}$ product that is beneficial for high-frequency switching applications. The results in this paper offer insights into important phenomena in tri-gate GaN devices and are fundamental for the further advance of this technology.

Linearity improvement in E‐mode ferroelectric GaN MOS‐HEMT using dual gate technology

In this work, an enhancement mode dual gate ferroelectric gallium nitride metal oxide semiconductor-high electron mobility transistor (GaN MOS-HEMT) is proposed with enhanced linearity characteristics. The different DC characteristics of the device are analysed and compared with available experimental data of single gate un-recessed ferroelectric GaN MOS-HEMT. In order to analyse the linearity performance of the devices, a look up table-based large signal model is developed directly from technology computer-aided device simulation results built by feeding different small signal parameters. The different linearity characteristics such as input third-order intercept point (IIP3), the input gain compression point (P1dB), third-order intermodulation (IM3) and the carrier to intermodulation power ratio of both the devices are compared by harmonic balance simulation of the developed large signal models. The interlink between IIP3 and IM3 with transconductance indicates that the broader the transconductance distribution with respect to different gate voltage generates higher IIP3 and lower IM3, which results in an improved linearity performance. The dual gate device shows improved linearity performance resulting in applicability in radiofrequency front end receiver.

Fabrication and Charge Deduction Based Sensitivity Analysis of GaN MOS-HEMT Device for Glucose, MIG, C-erbB-2, KIM-1, and PSA Detection

This paper presents the applicability of a high-resolution AlGaN/AlN/GaN metal oxide semiconductor-high electron mobility transistor (MOS-HEMT) for multiple bio detection and analysis of its sensitivity through a charge deduction based approach. The biomarkers of interest chosen in this paper include c-erbB-2, the breast cancer biomarker whose detection from saliva has been modeled. In this approach, the effective gate bias deduced through the model is applied to the fabricated device. High sensitivity of 0.054 mA/μgmL -1 , about nine times higher than the existing/conventional device, is attained here due to the modification of device epi design and use of MOS-gate. Similarly equivalent gate bias/interface charge has been deduced for other biomarkers such as prostate specific antigen, kidney injury molecule, monokine induced by interferon gamma, and glucose oxidase Enzyme, and effective sensitivities of 0.91 mA/μgmL -1 , 0.254 mA/μgmL -1 , 0.48 mA/ngmL -1 , and 2.06 mA/mmolL -1 , respectively, have been attained. The aim of the paper is developing an analytical model to analyze the sensitivity of the fabricated MOS-HEMT device with Al2O3 as gate dielectric (using on wafer testing) before the real packaging or sample introduction to ensure the device usability as a sensor for a dedicated detection. The methodology used here has been validated by comparison of the device sensitivity with real-time pH detection sensitivity. The device showcases high sensitivity of 1.83 mA/pH. The comparison of sensitivity with existing systems proves that the fabricated device overpowers the existing systems with huge marginal increase in sensitivities attained.

High-performance InAlGaN/GaN enhancement-mode MOS-HEMTs grown by pulsed metal organic chemical vapor deposition**Project supported by the National Postdoctoral Program for Innovative Talents, China (Grant No. BX201700184) and the National Key Research and Development Program of China (Grant Nos. 2016YFB0400105 and 2017YFB0403102).

Pulsed metal organic chemical vapor deposition was employed to grow nearly polarization matched InAlGaN/GaN heterostructures. A relatively low sheet carrier density of 1.8×1012 cm−2, together with a high electron mobility of , was obtained for the prepared heterostructures. The surface morphology of the heterostructures was also significantly improved, i.e., with a root mean square roughness of 0.29 nm in a scan area. In addition to the improved properties, the enhancement-mode metal–oxide–semiconductor high electron mobility transistors (MOS-HEMTs) processed on the heterostructures not only exhibited a high threshold voltage (VTH) of 3.1 V, but also demonstrated a significantly enhanced drain output current density of 669 mA/mm. These values probably represent the largest values obtained from the InAlGaN based enhancement-mode devices to the best of our knowledge. This study strongly indicates that the InAlGaN/GaN heterostructures grown by pulsed metal organic chemical vapor deposition could be promising for the applications of novel nitride-based electronic devices.

High-Performance AlGaN/GaN/Si Power MOSHEMTs With ZrO2 Gate Dielectric

We report on the power performance of GaN-on-Si metal–oxide–semiconductor high electron mobility transistors (MOSHEMTs) with a high- ${k}$ ZrO2 gate dielectric formed by atomic layer deposition. As a result of the high-quality ZrO2 and ZrO2/AlGaN interface, the MOSHEMTs demonstrate an excellent ON/OFF current ratio of $5 \times 10^{10}$ , a steep subthreshold slope of 66 mV/dec, a small hysteresis of ~0.05 V, and a high breakdown voltage of 1084 V at $1~\mu \text{A}$ /mm. Effective suppression of current collapse with a dynamic-to-static ON-resistance ratio of 1.78 at a drain bias of 600 V is also achieved in the device. Benefiting from the highly uniform gate stack, large-area devices with a gate width of 20 mm were also demonstrated using the ZrO2 gate dielectric, exhibiting a maximum output current of 7.4 A, a low ON-resistance of $0.66~\Omega $ , and a high breakdown voltage of 650 V at an OFF-state drain current of $1~\mu \text{A}$ /mm.

Thermal and Electrical Stability Assessment of AlGaN/GaN Metal–Oxide–Semiconductor High-Electron Mobility Transistors (MOS-HEMTs) With HfO2 Gate Dielectric

AlGaN/GaN high-electron mobility transistors (HEMTs) and metal–oxide–semiconductor (MOS)-HEMTs using HfO2 as a gate dielectric have been analyzed at room temperature, after short thermal annealing (STA) and thermal cycle tests, during off-state electrical step stress, high-temperature reverse bias (HTRB), and positive bias temperature instability (PBTI) tests. The results showed that the leakage current in as-fabricated MOS-HEMTs decreased by 106 and the on/off ratio increased by over 104 than the HEMTs. Moreover, it was even higher after an STA test, up to 108, in the MOS-HEMTs, and the surface trapping effects were mitigated, especially if a KOH cleaning was used before HfO2 deposition. The MOS-HEMTs also showed higher electrical stability after off-state step electrical stress, HTRB, and PBTI tests.

Improved AlGaN/GaN Metal–Oxide– Semiconductor High-Electron Mobility Transistors With TiO2Gate Dielectric Annealed in Nitrogen

An AlGaN/GaN metal–oxide–semiconductor high-electron mobility transistor (MOS-HEMT) that uses a high-k TiO2 gate insulator is demonstrated. TiO2 films are annealed at 300 °C and 600 °C in N2 or O2 following the deposition of an oxide layer. Experimental results reveal that the 300 °C N2-annealed TiO2/GaN MOS capacitor has the smallest interface traps of any of the studied devices. The 300 °C N2-annealed oxide interlayers between the GaN and the gate metal reduce the gate leakage current and improve the dc, high-frequency, and noise characteristics. The gate leakage current of the 300 °C N2-annealed MOS-HEMT is more than 3 orders of magnitude less than that of the baseline HEMT. This brief is the first to fabricate a GaN-based MOS-HEMT using an N2-annealed TiO2 gate insulator.

Quadruple Gate-Embedded T Structured GaN-Based Metal–Oxide–Semiconductor High-Electron Mobility Transistors

In this paper, high performance quadruple gate-embedded T structured GaN-based metal–oxide–semiconductor high-electron mobility transistors (MOSHEMTs) were fabricated using laser interference photolithography method and photoelectrochemical oxidation method, in which polymethylmethacrylate was used as sacrificial layer. The associated drain-source saturation current was improved to 175 mA/mm and the gate leakage current at the gate-source voltage of −80 V was improved to $0.81~\mu \text{A}$ compared with the 125 mA/mm and $7.6~\mu \text{A}$ of the conventional single gate GaN-based MOSHEMTs, respectively. Moreover, the associated maximum extrinsic transconductance of the quadruple gate-embedded T structured GaN-based MOSHEMTs was enhanced from 97.3 mS/mm to 118.4 mS/mm. Besides, the associated unit gain cutoff frequency and the associated maximum oscillation frequency were improved from 7.6 GHz to 10.8 GHz and from 11.4 GHz to 27.4 GHz, respectively. The improved performances of the quadruple gate-embedded T structure GaN-based MOSHEMTs were attributed to the function of the gate length reduction and the gate resistance decrease.

Current linearity and operation stability in Al2O3-gate AlGaN/GaN MOS high electron mobility transistors

To investigate current linearity and operation stability of metal–oxide–semiconductor (MOS) AlGaN/GaN high electron mobility transistors (HEMTs), we have fabricated and characterized the Al2O3-gate MOS-HEMTs without and with a bias annealing in air at 300 °C. Compared with the as-fabricated (unannealed) MOS HEMTs, the bias-annealed devices showed improved linearity of ID–VG curves even in the forward bias regime, resulting in increased maximum drain current. Lower subthreshold slope was also observed after bias annealing. From the precise capacitance–voltage analysis on a MOS diode fabricated on the AlGaN/GaN heterostructure, it was found that the bias annealing effectively reduced the state density at the Al2O3/AlGaN interface. This led to efficient modulation of the AlGaN surface potential close to the conduction band edge, resulting in good gate control of two-dimensional electron gas density even at forward bias. In addition, the bias-annealed MOS HEMT showed small threshold voltage shift after applying forward bias stress and stable operation even at high temperatures.