MESFET Research Articles

Thickness-dependent carrier transport and optically enhanced transconductance gain in III-VI multilayer InSe

Multilayer InSe with a thickness above ∼20 nm, is a direct semiconductor with a peak absorption wavelength approaching λ = 1000 nm, which is a promising candidate for solar-energy conversion and 2D optoelectronics devices. We present herein the experimental observations of thickness-dependent conductivity and photoconductive-responsivity spectrum in multilayer InSe as well as optically enhanced transconductance gain in the multilayer InSe metal-semiconductor-field-effect transistor (MESFET) illuminated by a halogen lamp. The voltage-current (V-I) measurement result shows multilayer InSe belongs to a p-type semiconductor, which can form a p-channel FET device. Thickness (t) dependent conductivity (σ) of multilayer InSe reveals about six-order variation from 5076 (Ω-cm)−1 (t = 5 nm) to 2.56 × 10−3 (Ω-cm)−1 (t = 184 μm, bulk) following a relationship of σ ∝ t−1.38. The highest conductivity in a thin InSe (e.g. t = 5 nm) is due to the increase of carrier density when the thickness is decreased. The photoresponsivity spectrum of a Ag-InSe-Ag multilayer photoconductor demonstrates a prominent peak absorption at 1.1 ∼ 1.3 eV, matches well with the direct-free-exciton energy of the InSe. A multilayer p-InSe MESFET was tested by V-I measurement. The transconductance was measured and determined to be The gm value will enhance about three times when the MESFET was placed under the illumination of a tungsten halogen lamp of a lower power density ∼0.5 mW · cm−2. All the experimental results demonstrate multilayer InSe a promising 2D material available for microelectronics and optoelectronics applications.

Silver oxide Schottky contacts and metal semiconductor field-effect transistors on SnO2 thin films

Silver oxide Schottky contacts (SCs), reactively sputtered using a low-power Ar:O2 rf-plasma on SnO2 films grown by mist-CVD, showed significantly improved figures-of-merit compared with plain-metal SCs, with barrier heights of 0.91 eV and ideality factors close to unity. These SCs were used to fabricate thin-film metal-semiconductor FETs with on/off ratios >106 on the same solution-processed material. It is proposed that the high quality of these SCs is due to the oxidized fabrication methodology, whereby reactive oxygen species are likely to be present during the formation of the Schottky interface, leading to the removal of the native surface electron accumulation layer.

Comment on “Metal Semiconductor Field-Effect Transistor with MoS2/Conducting NiOx van der Waals Schottky Interface for Intrinsic High Mobility and Photoswitching Speed”

Molybdenum disulfide (MoS2) nanosheet, one of two-dimensional (2D) semiconductors, has recently been regarded as a promising material to break through the limit of present semiconductors. With an apparent energy band gap, it certainly provides a high carrier mobility, superior subthreshold swing, and ON/OFF ratio in field-effect transistors (FETs). However, its potential in carrier mobility has still been depreciated since the field-effect mobilities have only been measured from metal–insulator–semiconductor (MIS) FETs, where the transport behavior of conducting carriers located at the insulator/MoS2 interface is unavoidably interfered by the interface traps and gate voltage. Moreover, thin MoS2 MISFETs have always shown large hysteresis with unpredictable negative threshold voltages. Here, we for the first time report MoS2-based metal semiconductor field-effect transistors (MESFETs) using NiOx Schottky electrode which makes van der Waals interface with MoS2. We thus expect that the maximum mobilities or ...

A top-gate GaN nanowire metal–semiconductor field effect transistor with improved channel electrostatic control

A uniformly n-type doped GaN:Si nanowire (NW), with a diameter of d = 90 nm and a length of 1.2 μm, is processed into a metal-semiconductor field effect transistor (MESFET) with a semi-cylindrical top Ti/Au Schottky gate. The FET is in a normally-ON mode, with the threshold at −0.7 V and transconductance of gm ∼ 2 μS (the transconductance normalized with NW diameter gm/d > 22 mS/mm). It enters the saturation mode at VDS ∼ 4.5 V, with the maximum measured drain current IDS = 5.0 μA and the current density exceeding JDS > 78 kA/cm2.

Recent progress in Ga2O3 power devices

This is a review article on the current status and future prospects of the research and development on gallium oxide (Ga2O3) power devices. Ga2O3 possesses excellent material properties, in particular for power device applications. It is also attractive from an industrial viewpoint since large-size, high-quality wafers can be manufactured from a single-crystal bulk synthesized by melt–growth methods. These two features have drawn much attention to Ga2O3 as a new wide bandgap semiconductor following SiC and GaN. In this review, we describe the recent progress in the research and development on fundamental technologies of Ga2O3 devices, covering single-crystal bulk and wafer production, homoepitaxial thin film growth by molecular beam epitaxy and halide vapor phase epitaxy, as well as device processing and characterization of metal–semiconductor field-effect transistors, metal–oxide–semiconductor field-effect transistors and Schottky barrier diodes.

A novel high-performance high-frequency SOI MESFET by the damped electric field

In this paper, we introduce a novel silicon-on-insulator (SOI) metal-semiconductor field-effect-transistor (MESFET) using the damped electric field (DEF). The proposed structure is geometrically symmetric and compatible with common SOI CMOS fabrication processes. It has two additional oxide regions under the side gates in order to improve DC and RF characteristics of the DEF structure due to changes in the electrical potential, the electrical field distributions, and rearrangement of the charge carriers. Improvement of device performance is investigated by two-dimensional and two-carrier simulation of fundamental parameters such as breakdown voltage (VBR), drain current (ID), output power density (Pmax), transconductance (gm), gate–drain and gate–source capacitances, cut-off frequency (fT), unilateral power gain (U), current gain (h21), maximum available gain (MAG), and minimum noise figure (Fmin). The results show that proposed structure operates with higher performances in comparison with the similar conventional SOI structure.

Stability of In-Ga-Zn-O metal-semiconductor field-effect-transistors under bias, illumination, and temperature stress

The stability of metal-semiconductor field-effect-transistors (MESFETs) with silver oxide Schottky gates on In-Ga-Zn-O (IGZO) channels, grown by mist chemical-vapor-deposition, was examined under different combinations of positive and negative bias, illumination, and temperature stress. These devices were remarkably stable, even under the most severe condition of negative-bias-illumination-temperature-stress (NBITS), where the threshold voltage shift after 10 h NBITS was only +0.12 V and was mainly attributed to a decrease in the carrier density of the channel. The stability of these IGZO MESFETs is associated with the use of a conducting Schottky gate that significantly reduces charge trapping at the gate-channel interface.

A novel symmetrical 4H–SiC MESFET: an effective way to improve the breakdown voltage

In this paper, a novel symmetrical structure (SS) of 4H---SiC metal semiconductor field effect transistor (MESFET) as an effective way to improve the breakdown voltage is presented. The key idea in this work is to improve the breakdown voltage, maximum output power density, and frequency parameters of the device using a symmetrical structure with recessed gate. The SS-MESFET modifies the electric field in the drift layer significantly. The influence of the SS-MESFET on the saturation current, breakdown voltage $$(\hbox {V}_{\mathrm{BR}})$$(VBR), and small-signal characteristics of the SS-MESFET are studied by numerical device simulation. Using two-dimensional device simulation, we demonstrate that the breakdown voltage $$(\hbox {V}_{\mathrm{BR}})$$(VBR) improved by factors 2.5 and 3.3 in comparison with an asymmetrical conventional MESFET structure (AC-MESFET) and a symmetrical conventional MESFET structure (SC-MESFET), respectively. Also, the maximum output power density $$(\hbox {P}_{\mathrm{max}})$$(Pmax) improved about by 93 and 250 % in comparison with the AC-MESFET and SC-MESFET structures, respectively. So, the SS-MESFET shows the superior maximum available gain (MAG), unilateral power gain (U), and current gain $$(\hbox {h}_{12})$$(h12) which is presenting the proposed structure is more suitable device for high power microwave applications.

Improved multi-recessed 4H–SiC MESFETs with double-recessed p-buffer layer

An improved multi-recessed 4H–SiC metal semiconductor field effect transistor (MRD-MESFET) with double-recessed p-buffer layer (DRB-MESFET) is proposed in this paper. By introducing a double-recessed p-buffer layer, the gate depletion layer is further modulated, and higher drain saturation current and DC transconductance are obtained compared with the MRD-MESFET. The simulations show that the drain saturation current of the DRB-MESFET is about 42.4% larger than that of the MRD-MESFET. The DC transconductance of the DRB-MESFET is almost 15% higher than that of the MRD-MESFET and very close to that of double-recessed structure (DR-MESFET) at the bias conditions of Vgs=0V and Vds=40V. The proposed structure has an improvement of 26.1% and 74.2% in the output maximum power density compared with that of the MRD-MESFET and DR-MESFET, respectively. In the meanwhile, the proposed structure possesses smaller gate-source capacitance, which results in better RF characteristics.

A novel 4H-SiC MESFET with ultrahigh upper gate

A novel 4H-SiC metal semiconductor field effect transistor with ultrahigh upper gate (UU-MESFET) by depletion layer variation and electric field modulation is proposed in this paper for the first time. The prominent merits in the proposed structure are the smaller gate depletion layer and the higher electric field peak produced by the electric field modulation due to ultrahigh upper gate. A higher electric field peak is introduced by ultrahigh upper gate at lower gate corner instead of upper gate corner, which leads to electric field breakdown. Using ISE simulation, the breakdown voltage of the UU-MESFET is improved by 55% and the drain saturation current is increased by 15% than those of the conventional DR-MESFET, which means that the UU-MESFET has an improvement of about 78% in the maximum output power density compared to the DR-MESFET. Furthermore, the gate–source capacitance of the proposed structure is about 17% smaller than that of the DR-MESFET. Therefore the proposed structure has fantastic DC performance and in the meanwhile possesses better RF characteristics.

Metal Semiconductor Field-Effect Transistor with MoS2/Conducting NiO(x) van der Waals Schottky Interface for Intrinsic High Mobility and Photoswitching Speed.

Molybdenum disulfide (MoS2) nanosheet, one of two-dimensional (2D) semiconductors, has recently been regarded as a promising material to break through the limit of present semiconductors. With an apparent energy band gap, it certainly provides a high carrier mobility, superior subthreshold swing, and ON/OFF ratio in field-effect transistors (FETs). However, its potential in carrier mobility has still been depreciated since the field-effect mobilities have only been measured from metal-insulator-semiconductor (MIS) FETs, where the transport behavior of conducting carriers located at the insulator/MoS2 interface is unavoidably interfered by the interface traps and gate voltage. Moreover, thin MoS2 MISFETs have always shown large hysteresis with unpredictable negative threshold voltages. Here, we for the first time report MoS2-based metal semiconductor field-effect transistors (MESFETs) using NiOx Schottky electrode which makes van der Waals interface with MoS2. We thus expect that the maximum mobilities or carrier transport behavior of the Schottky devices may hardly be interfered by interface traps or an on-state gate field. Our MESFETs with a few and ∼10 layer MoS2 demonstrate intrinsic-like high mobilities of 500-1200 cm(2)/(V s) at a certain low threshold voltage between -1 and -2 V without much hysteresis. Moreover, they work as a high speed and highly sensitive phototransistor with 2 ms switching and ∼5000 A/W, respectively, supporting their high intrinsic mobility results.

Transparent Amorphous Ru–Si–O Schottky Contacts to In–Ga–Zn–O

Transparent amorphous oxide semiconductors (TAOSs), such as In-Ga-Zn-O (a-IGZO), are the subject of intensive experimental and theoretical research aimed at applications in transparent electronics. With the development of novel device applications came an increased demand for the understanding and control of a-IGZO Schottky contact properties. Rectifying contacts are suitable for the development of Schottky diodes and metal-semiconductor field-effect transistors (MESFETs) for fast and low power consumption integrated circuits and active-matrix displays. We propose fabrication of Schottky barrier to a-IGZO based on transparent conductive oxide (TCO), namely Ru-Si-O. We have found that atomic composition and microstructure of this TCO are effective in preventing interfacial reactions in the contact region which allows to avoid pre-treatment of the semiconductor surface. Ru-Si-O Schottky contacts to a-IGZO have been fabricated by means of reactive sputter-deposition. We provide comprehensive results on effects of Ru-Si-O chemical composition on properties of rectifying contacts to a-IGZO. Depending on oxygen content in Ru-Si-O sputtering atmosphere, for a specific process window (from 10% to 20% of O2 in sputtering atmosphere), highly rectifying transparent Schottky barriers are obtained without additional a-IGZO surface treatment.

Velocity overshoot decay mechanisms in compound semiconductor field-effect transistors with a submicron characteristic length

Velocity overshoot is a critically important nonstationary effect utilized for the enhanced performance of submicron field-effect devices fabricated with high-electron-mobility compound semiconductors. However, the physical mechanisms of velocity overshoot decay dynamics in the devices are not known in detail. Therefore, a numerical analysis is conducted typically for a submicron GaAs metal-semiconductor field-effect transistor in order to elucidate the physical mechanisms. It is found that there exist three different mechanisms, depending on device bias conditions. Specifically, at large drain biases corresponding to the saturation drain current (dc) region, the velocity overshoot suddenly begins to drop very sensitively due to the onset of a rapid decrease of the momentum relaxation time, not the mobility, arising from the effect of velocity-randomizing intervalley scattering. It then continues to drop rapidly and decays completely by severe mobility reduction due to intervalley scattering. On the other hand, at small drain biases corresponding to the linear dc region, the velocity overshoot suddenly begins to drop very sensitively due to the onset of a rapid increase of thermal energy diffusion by electrons in the channel of the gate. It then continues to drop rapidly for a certain channel distance due to the increasing thermal energy diffusion effect, and later completely decays by a sharply decreasing electric field. Moreover, at drain biases close to a dc saturation voltage, the mechanism is a mixture of the above two bias conditions. It is suggested that a large secondary-valley energy separation is essential to increase the performance of submicron devices.

Defect evaluation in InGaAs field effect transistors with HfO2 or Al2O3 dielectric

The performance of InGaAs metal oxide semiconductor field effect transistors with Al2O3 or HfO2 as gate oxide is evaluated and compared. The Al2O3 transistors show the lowest subthreshold slope and mid gap Dit, however, the HfO2 transistors reach a higher maximum transconductance (gmax) due to the higher oxide capacitance. Both high-κ dielectrics show a gm-frequency dispersion due to tunneling into border traps with a negligible activation energy as determined from temperature dependent measurements. The total amount of trapped charge at border traps is lower in the HfO2 devices. Scaling the HfO2 thickness further reduces the gm-frequency dispersion, possibly due to detrapping to the gate electrode.

Metal-Semiconductor Field-Effect Transistors With In–Ga–Zn–O Channel Grown by Nonvacuum-Processed Mist Chemical Vapor Deposition

In-Ga-Zn-O (IGZO) thin films (TFs) were grown by cost-effective nonvacuum solution-processed mist chemical vapor deposition. High quality AgO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Schottky contacts (SCs) were fabricated on these IGZO TFs with rectification ratios and barrier heights as high as 7.9 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> and 1 eV, respectively, combined with ideality factors as low as 1.32. These SCs were subsequently used as gate contacts in the production of metal-semiconductor field-effect transistors (MESFETs) with excellent switching and stability characteristics. For example, typical (W/L 785 μm/5 μm) MESFETs were capable of providing ON-currents up to 245 μA, combined with a large ON/OFF ratio of 3.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> . A mobility of 3.2 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /(V.s) and a low subthreshold swing of 356 mV/decade were achieved in the W/L 524 μm/10 μm transistors. Under positive bias stress, these MESFETs were highly stable, demonstrating the feasibility of using a combination of mist chemical vapor deposition grown IGZO and AgO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> SCs to produce stable, low power consumption, and low-cost switching devices.

Enhancement of Ru–Si–O/In–Ga–Zn–O MESFET Performance by Reducing Depletion Region Trap Density

In this letter, we investigated the effect of magnetron cathode current (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) during reactive sputtering of In-Ga-Zn-O (a-IGZO) channel layer on properties of metal-semiconductor field-effect transistors with Ru-Si-O Schottky gate electrode. One can observe that as I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> increased from 90 to 150 mA channel mobility (μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ch</sub> ) and subthreshold swing (S) improved from μch = 7.5 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V·s and S = 580 V/dec to μch = 8.8 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V ·s and S = 420 V/dec, respectively. This enhancement in transistors performance was attributed to the reduction of charge density in the depletion region of Ru-Si-O/In-Ga-Zn-O Schottky contacts, which we assigned to the densification of a-IGZO films fabricated at higher I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> .

A novel 4H–SiC MESFET with clival gate

In this paper, a novel 4H–SiC metal semiconductor field effect transistor (MESFET) with a clival gate structure (CG-MESFET) is proposed. The drain current (ID) and the breakdown voltage (VB) are simulated and compared to the traditional double-recessed gate 4H–SiC MESFET (DR-MESFET). The results indicate that the drain current (ID) of the CG-MESFET transforms with the change of end point of clival gate (EPCG), and it reaches to a maximum value about 545mA when EPCG is at 1/2 of whole gate, thus, the drain current (ID) has a much greater increase than that of the DR-MESFET. The CG-MESFET has the advantages of high breakdown voltage (VB) that is increased by 15% and superior DC performances over the DR-MESFET.

A Novel MESFET structure by U-shape buried oxide for improving the DC and RF Characteristics

For the first time, a new type of silicon on insulator metal semiconductor field-effect transistor (SOI-MESFET), the U-shape buried oxide (UBO) SOI-MESFET, is proposed and investigated. The proposed structure is similar to that of the conventional SOI-MESFET with the exception that the shape of buried oxide is reformed to the U-shape. The influence of U-shape buried oxide on saturation current (ID), breakdown voltage (VBR), and small-signal characteristics of the UBO-SOI MESFET is studied by numerical device simulation and compared with a conventional SOI MESFET (C-SOI MESFET) characteristics. The simulated results show that the U-shape buried oxide has excellent effect on cut-off frequency (fT), maximum oscillation frequency (fmax), maximum available gain (MAG), and unilateral power gain (U) for the UBO-SOI MESFET structure. Also the U-shape buried oxide leads to the enhancement of VBR and ID of the UBO-SOI MESFET structure. The optimized results showed that VBR of the UBO-SOI MESFET is 77% larger than that of the C-SOI MESFET, which meanwhile maintains almost 90% higher saturation drain current characteristics. The maximum output power densities of 0.05 and 0.014W/mm are obtained for the UBO-SOI and C- SOI MESFET structures, respectively, which means about 3.5 times larger output power for the proposed device.

Effect of Schottky gate type and channel defects on the stability of transparent ZnO MESFETs

Transparent metal–semiconductor field-effect transistors (MESFETs) were fabricated on ZnO thin films deposited using a filtered cathodic vacuum arc. MESFETs with silver oxide (AgOx) and iridium oxide (IrOx) Schottky gates with mobilities up to 70 cm2 V−1 s−1 were subjected to extensive bias and illumination stress tests. Device instability appeared to be strongly dependent on gate metal type, bias conditions and ZnO film morphology. Positive bias stress of AgOx gated devices resulted in irreversible damage that is thought to be due to Ag electromigration across the gate interface. IrOx gated devices showed superior stability with only a small recoverable decay in channel current that was associated with the charging of grain boundary defects.

Low frequency noise of ZnO based metal-semiconductor field-effect transistors

The low frequency noise of metal-semiconductor field-effect transistors (MESFETs) based on ZnO:Mg thin films grown by pulsed laser deposition on a-plane sapphire was investigated. In order to distinguish between noise generation in the bulk channel material, at the semiconductor surface, and at the gate/channel interface, ohmic ZnO channels without gate were investigated in detail, especially concerning the dependency of the noise on geometrical variations. The experiments suggest that the dominating 1/f noise in the frequency range below 1 kHz is generated within the bulk channel material, both for bare ZnO channels and MESFETs.