GaAs Metal-semiconductor Field-effect Transistors Research Articles

Visible Range Characterization of Au/Graphene-GaAs Schottky Junctions in MESFET

We report the simulated visible range characteristics of gold (Au)/graphene-GaAs Schottky junctions in MESFET (Metal–Semiconductor Field Effect Transistor) under photovoltaic, forward bias, and reverse bias conditions. The devices exhibit high photoresponse in zero bias conditions, moderate response under applied reverse bias, and zero photoresponse in forward bias conditions. We discuss in detail the factors involved in the attained response and provide comparative analysis of the studied devices with our previously published work on ultraviolet (UV) characterization demonstrating moderate response under both zero bias and reverse bias, and z ero response under forward bias. We also perform comparison of our theoretical results with the literature showing enhanced or comparable performance. The simulation model is validated with the experimental results reported elsewhere as well as with the commercially available software (Visual TCAD) simulations. The GaAs MESFET Schottky junctions will serve good purpose in UV-visible applications.

Six-Port Direct Modulator With Carrier Suppression Technology for High-Speed High-Frequency Wireless Communications

In this letter, a six-port direct modulator with carrier leakage suppression is proposed and experimentally demonstrated for downlinks in the future high-speed high-carrier-frequency wireless communication systems. To handle high carrier frequencies and provide good performance, GaAs metal–semiconductor field-effect transistor RF switches are used to complete the modulation. Up to 500-MBd quadrature phase shift keying signals at 24 GHz are generated and evaluated in our system. Moreover, the proposed six-port modulator is easy to integrate with the optical link and modulated signals at 24 GHz are evaluated after transmission over up to 20-km standard single mode fiber.

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.

Analytical modelling of the current ( I )–voltage ( V ) characteristics of sub‐micron gate‐length ion‐implanted GaAs MESFETs under dark and illuminated conditions

An analytical model for current (I)–voltage (V) characteristics of a short-channel ion-implanted GaAs MESFET has been presented for dark and illuminated conditions. For the sake of simplicity, the non-analytic (i.e. non-integral) Gaussian doping function commonly considered for the channel doping of an ion-implanted GaAs metal semiconductor field effect transistor (MESFET) has been replaced by an analytic Gaussian-like doping profile in the vertical direction. The device uses an indium–tin oxide-based Schottky gate through which an optical radiation of 0.87 μm wavelength is coupled from an external source into the device to modulate the I–V characteristics of the short-gate length GaAs MESFET. The coupled light generates electron–hole pairs in the active channel region below the gate and develops a photovoltage across the Schottky gate–channel junction and modulates the device characteristics. This study also includes the modelling of this photovoltaic effect by taking the short-gate length effects into consideration. The developed model includes the effects of doping profile and device parameters on the drain current of the short-channel ion-implanted GaAs MESFETs under dark and illuminated conditions of operations. The accuracy of the proposed model is extensively verified by comparing the theoretically predicted results with numerical simulation data obtained by using the commercially available ATLASTM device simulation software.

Numerical analysis of formation properties of a high-field dipole domain for submicron GaAs field-effect transistor devices

A typical 0.3-μm gate-length submicron GaAs metal-semiconductor field-effect transistor (MESFET) is simulated using a complete energy model that solves a complete form of the energy conservation equation, and also using a simplified energy model that only neglects heat flux for electrons. The simulations are carried out with the same device physical and bias conditions, and a transient analysis is made to investigate thermal electron conduction effects on the formation property of a high-field dipole domain in the submicron GaAs MESFET. It is shown that the simplified model leads to the existence of a very unstable Gunn domain oscillating between the gate and drain, but the more accurate complete model gives a stable high-field domain confined well in the gate region due to thermal electron conduction. The crucial reason for this discrepancy between the two results is associated with the capable limits of accuracy in the simplified model. That is, this model gives rise to an unduly large retardation in the energy-gaining rate of electrons in the gate channel, so that the production of the negative differential resistance phenomenon by the electrons is largely delayed under the gate. Therefore, a traveling Gunn domain can be exhibited for submicron GaAs field-effect transistors in the simulation by a simplified energy model. It is demonstrated that even though simplified energy models are capable of reflecting the nonstationary effect of velocity overshoot properly, it is quite improper to apply these for studying device physics related to dipole domain properties; thermal electron conduction plays a pivotal role in forming a stable dipole domain in the submicron GaAs MESFET. In addition, the average effective valley-transition force for channel electrons (a new physical quantity first defined in the paper) is used to show that simplified energy models give a much larger magnitude for the force (approximately 1.8 eV/μm) compared to 1.2 eV/μm given by the complete energy model. Furthermore, the force is given closer to the drain end of the gate in the former models. Therefore, simplified energy models have a high possibility of creating a traveling domain for submicron devices.

Channel Direction Effect on the GaAs Mesfet Performances for MEMS Accelerometer Application

An experimental investigation has been carried out with clarifying the external mechanical stress effect on GaAs metal-semiconductor field-effect transistor (MESFET) I-V characteristic curve which as the sensitive element of micro-accelerometer in different condition. In this paper, we research different channel directions to explore the output characteristics of the GaAs MESFET which fabricated at the root of the cantilever. We design three channel directions which angled with the cantilever as 0 degree, 45 degree, 90 degree. We find that when the Channel direction parallel to the cantilever direction, ∆U has the maximum value of 12.13mv. The sensitivity of 0 degree is 0.04mv/g higher than the 90 degree. The dynamic result indicates that the channel direction parallel to the cantilever direction is the optimized design structure.

Current oscillations and low-frequency noises in GaAs MESFET channels with sidegating bias

Low-frequency noises (LFN) and noise-like oscillations (NLO) in GaAs metal semiconductor field effect transistor (MESFET) channel current were investigated under sidegating bias conditions. It was found that the fluctuations of the channel current were directly dependent upon the sidegating bias. As the sidegating bias decreased, the amplitudes of the oscillations would increase correspondingly. Furthermore, the LFN and NLO would attenuate sharply when the sidegating bias increased to more than a certain voltage. Two mechanisms are presented to demonstrate that the effective substrate resistivity or the channel-substrate junction modulated by sidegating bias and deep level traps would take responsibilities for the LFN and NLO.

Two-Dimensional Analysis of Field-Plate Effects on Surface-State-Related Current Transients and Power Slump in GaAs FETs

In this paper, we carry out a 2-D transient analysis of field-plate GaAs metal-semiconductor field-effect transistors (FETs) by taking surface states into account. Quasi-pulsed current-voltage curves are derived from the transient characteristics. We show that drain lag and current slump (power slump) due to surface states are reduced by introducing a field plate because the fixed potential at the field plate mitigates the trapping effects of the surface states. The dependence of lag and current slump on the field-plate length and the passivation layer thickness is also studied. We show that it is possible to reduce the current slump and maintain the high-frequency performance of GaAs FETs at optimum values of the field-plate length and the layer thickness.

MESFET DC model parameter extraction using Quantum Particle Swarm Optimization

This paper presents two techniques for DC model parameter extraction for a Gallium Arsenide (GaAs) based MEtal Semiconductor Field Effect Transistor (MESFET) device. The proposed methods uses Particle Swarm Optimization (PSO) and Quantum Particle Swarm Optimization (QPSO) methods for optimizing the difference between measured data and simulated data. Simulated data are obtained by using four different popular DC models. These techniques avoid complex computational steps involved in traditional parameter extraction techniques. The performance comparison in terms of quality of solution and execution time of classical PSO and QPSO to extract the model parameters are presented. The validity of this approach is verified by comparing the simulated and measured results of a fabricated GaAs MESFET device with gate length of 0.7 μm and gate width of 600 μm (4 × 150). Simulation results indicate that both the technique based on PSO and QPSO accurately extracts the model parameters of MESFET.

Compact modeling of a PD SOI MESFET for wide temperature designs

A compact model for the partially depleted (PD) silicon-on-insulator (SOI) metal semiconductor field effect transistor (MESFET) is presented. The absence of a gate-oxide makes the SOI MESFET extremely robust, able to withstand high voltages, and useful for extreme environment electronics. These devices have been fabricated using a standard SOI CMOS process. In contrast to SOI MOSFETs and GaAs MESFETs, the source–substrate voltage has a significant impact on the channel current. In this work a model has been developed that includes the effect of the buried oxide on the performance of the MESFET. The model has been verified for a wide temperature range of −180 to 150°C. A behavioral model has been included to model the breakdown voltage. The core DC and RF models have been adapted from the commercially available Triquint's Own Model (TOM3) MESFET model. Building from the TOM3 model, a measurement-based approach is used to develop a four-terminal compact model using Verilog-A. The charge-based approach, using S-parameter measurements was used to develop the capacitance model. We also present a voltage reference circuit using two MESFET transistors to verify the model and explore wide temperature range circuit applications.

Accurate and Efficient Modeling of FET Cold Noise Sources Using ANNs

Accurate and efficient models of the available output noise temperature of a field-effect transistor (FET) cold noise source were developed using artificial neural networks (ANNs). Radial basis function and backpropagation (BP) architectures were used for this application, and the models were obtained from measured data of a gallium arsenide (GaAs) metal-semiconductor FET (MESFET) with a gate width and a 0.25-mum gate length. Two-input one-output ANNs were developed for incident noise temperature versus load reflection coefficient, as well as incident noise temperature versus load impedance for different percentages of training data. The most accurate model was a BP network that used 75% of the measured data and the Levenberg-Marquardt algorithm for training and was for incident noise temperature versus load impedance with average relative error (ARE) and maximum local relative error (MLRE) values of 0.1439% and 1.1544%, respectively. The most efficient model was a BP network that used only 42% of the measured data and the resilient backpropagation algorithm for training and was for incident noise temperature versus load impedance with an ARE of 0.1940% and an MLRE of less than 5%. To further validate the modeling process, a set of measured data from a GaAs MESFET with a gate width and a 0.25- gate length was used with the architecture of the previous models to develop new models. All results demonstrated that ANNs can accurately and efficiently predict incident noise temperature of cold noise sources.

New Time-Domain Voltage and Current Waveform Measurement Setup for Power Amplifier Characterization and Optimization

This paper reports a novel voltage and current waveform measurement system suitable for large-signal transistor and power amplifier characterization and optimization. This technique is original in its use of a double six-port (SP) reflectometer as a homodyne vector network analyzer, which is calibrated in magnitude and phase by means of a reference multiharmonic signal generator, to measure the waveforms at the output terminal of the device. An active branch load-pull setup is used to control the source impedance at the fundamental frequency, and the load impedance at the fundamental, second, and third harmonic frequencies. The capability of the proposed SP reflectometer-based configuration is demonstrated experimentally, by measuring the voltage and current waveforms of a GaAs metal-semiconductor field-effect transistor that is biased in class AB and tuned for maximum efficiency. To assess the level of accuracy of the proposed method, the same waveforms were also measured using a microwave-transition-analyzer-based system. A comparison of the results shows that the proposed SP reflectometer setup obtains results accurate enough for power amplifier characterization with lower equipment cost.

An Improved Model for GaAs MESFETs Suitable for a Wide Bias Range

In this letter, we present a new large signal model for GaAs metal-semiconductor field effect transistors, incorporating features for enhancing the bias range for which accuracy is maintained, for use in the simulation of microwave circuits. The model parameters for a specific case were extracted from a wide range of dc I-V and S-parameter data, and the simulated behavior was observed to match the measured data closely. The model includes the possibility of showing negative slopes of the I-V curves at high power without sacrificing accuracy in predicting radio frequency behavior, while remaining simple enough for use in simulation tools

Development of a large-force low-loss metal-contact RF MEMS switch

We improved the large restoration force of a radio-frequency microelectromechanical system (RF MEMS) switch, which had been a challenge in the practical application of RF MEMS switches, by adopting a non-linear spring system for the electrostatic actuator. When an electrostatic actuator with a movable electrode area of 1.4 mm 2 was driven at a voltage of 24 V, analysis showed a restoration force three-fold greater than that of conventional linear spring systems and a stable signal on–off control action. It was also established from simulation and observation of the RF characteristics in a plastic mold package that the actuator has the ability comparable to or exceeding the characteristics of positive intrinsic negative (PIN) diodes and GaAs metal-semiconductor field-effect transistors (MESFETs).

A speed and accuracy test of backpropagation and RBF neural networks for small-signal models of active devices

Backpropagation networks are compared to radial basis function (RBF) networks when it comes to small signal modeling RF/microwave active devices. The modeled device is a 4×50 μm gate width, 0.25 μm gate length gallium arsenide (GaAs) Metal semiconductor field-effect transistor (MESFET). It is the authors’ intent to prove that RBF networks provide much better performance than backpropagation when it comes to this type of modeling. First, two separate backpropagation networks are created to determine the best training algorithm in terms of convergence speed. Then, the backpropagation network, using its best training algorithm, is compared to the RBF network in terms of speed and accuracy. Simulation results are presented in tables and figures for better understanding. All tests and simulations for the backpropagation and RBF networks are done using Matlab's Neural Network Toolbox.

A cryogenic voltage amplifier with 36MHz bandwidth using discrete GaAs metal-semiconductor field-effect transistors

We report a design procedure and performance of a voltage amplifier using commercially available GaAs metal-semiconductor field-effect transistors. There are two stages: a common-source amplifier that provides a moderate gain, followed by a common-drain stage for driving the 50Ω coaxial cable. The overall voltage gain measured at 4.2K with a 50Ω load is 3.3, with a bandwidth of 36MHz. The input-referred voltage noise is measured to be approximately 3.2nV∕√Hz in a wide frequency range.

Analysis of DC Characteristics and Small Signal Equivalent Circuit Parameters of GaAs Metal–Semiconductor Field Effect Transistors with Different Gate Lengths and Different Gate Contours by Two-Dimensional Device Simulations

The gate length and gate contour of a GaAs metal–semiconductor field effect transistor (MESFET) device play important roles in determining the small signal circuit parameters and large signal breakdown voltage behavior. GaAs MESFETs with different gate lengths and gate contours were studied by the two-dimensional (2-D) semiconductor device simulations to investigate the dependence of small signal circuit parameters and breakdown voltage on gate length and gate contour. The results show that gate length affects small-signal circuit parameter Cgs while gate contour affects Cgd. The breakdown voltage has strong dependence on gate contour and little dependence on gate length.

Application of a Scanning Thermal Nano-Probe for Thermal Imaging of High Frequency Active devices

The first application of a new thermal nano-probe based on the changes of electrical resistivity of a nanometer-sized filament with temperature has been presented for the thermal imaging of microwave power active devices. The integration of the filament the fabrication process of the novel thermal probe with a spatial resolution better than 80 nm and a thermal resolution of the order of 10-3 K have already been presented in reference [J. Microelectron. Eng. 57–58 (2001) 737]. To demonstrate the capability of the novel thermal nano-probe the measurements have been successfully performed on a 30 fingers GaAs metal–semiconductor field-effect transistor (GaAs-MESFET) with a maximum power dissipation of 2.5 W. The bias circuit has been designed to suppress the undesired microwave oscillations in the transistor. In this case the power dissipation is equal to the dc power input. The near-field measurements using the nano-probe are compared with infrared measurement and three-dimensional finite element static thermal simulations. The good agreement between simulations and measurements confirms the high capability of the nono-probe for these applications.

Bendable GaAs metal-semiconductor field-effect transistors formed with printed GaAs wire arrays on plastic substrates

Micro/nanowires of GaAs with integrated ohmic contacts have been prepared from bulk wafers by metal deposition and patterning, high-temperature annealing, and anisotropic chemical etching. These wires provide a unique type of material for high-performance devices that can be built directly on a wide range of unusual device substrates, such as plastic or paper. In particular, transfer printing organized arrays of these wires at low temperatures onto plastic substrates yield high-quality bendable metal-semiconductor field-effect transistors. Electrical and mechanical characterization of devices on poly(ethylene terephthalate) illustrates the level of performance that can be achieved. These results indicate promise for this approach to high-speed flexible circuits for emerging applications in consumer and military electronic systems.

Noise Analysis of GaAs-MESFETs by Physics-Based Circuit Simulator Employing Monte Carlo Technique

SUMMARY Noise characteristics of GaAs metal-semiconductor field effect transistors (GaAs-MESFETs) with scaled-down dimensions are analyzed and modeled using a physics-based circuit simulator employing the Monte Carlo (MC) particle technique. The microscopic dynamics of electrons is also analyzed to investigate the mechanism of noise generation in a channel. Noise spectral densities of GaAs-MESFETs with two different geometries are estimated by evaluating fluctuations in instantaneous terminal currents. Then, minimum noise figures, Fmin, and noise figure circles are estimated using the noise spectral densities and Y-parameters. Because of an increase in y21 and suppression of an increase of noise spectral density, the device with an n+-region extending to below the drain-side edge of the gate contact exhibits a smaller noise figure. Suppression of the electron velocity fluctuation caused by electron transitions to higher valleys in a high electric field region is responsible for the noise suppression.