GaAs Field-effect Transistors Research Articles

Model of interface states at III-V oxide interfaces

We present a generalized model of the density of interface states at III-V oxide interfaces. The states are based on the native defects such as dangling bonds on the Ga and As sites or As–As bonds created by oxidation. The model explains the difficulty of n-type operation for GaAs field effect transistors (FETs) compared to GaAs pFETs or to InGaAs nFETs.

Analysis and design of high-efficiency variable conduction angle Doherty amplifier

The Doherty amplifier was first proposed to improve the efficiency under output power back-off using the technique of load-line modulation of a ‘carrier’ amplifier through a ‘peak’ amplifier. By varying input bias of the peak amplifier along with load of the carrier amplifier at low drive levels, different topologies of the Doherty amplifier are distinguished. An analytical analysis that determines the optimum output performance of these topologies in terms of output power, efficiency and output power back-off ensuring a near-peak efficiency is developed. The presented comprehensive analysis considered for variation of conduction angle of the peak amplifier biased class C. New design equations of the analysed topologies are derived. A realisation at a central frequency of 1.9 GHz using GaAs field effect transistor (FET) devices of a Doherty amplifier topology is reported. In this topology the carrier operates (at low drive levels) into load impedance 5/2 times larger than its optimum. Power-added efficiency of 61.8% is measured at P1 dB of 25.9 dB m and 33.2% is measured at 9 dB back-off from P1 dB.

Room temperature terahertz detection based on bulk plasmons in antenna-coupled GaAs field effect transistors

A first generation of antenna-coupled GaAs metal-semiconductor-field-effect-transistors (MESFETs) is fabricated, modeled, and tested for room-temperature terahertz detection. For fixed excitation frequencies between 0.14 and 1THz, the source-drain current (signal) is monitored as the gate and drain voltages are varied. The signal shows resonances when applied voltages sweep the charge density in the MESFET through values at which the bulk plasmon is resonant with the excitation frequency. For these unoptimized devices, the measured system noise-equivalent power is ∼5×10−8W∕Hz1∕2; the electronics-limited response time is 10ns.

Thermal Transient Response of GaAs FETs Under Intentional Electromagnetic Interference (IEMI)

Transient thermal responses of GaAs field-effect transistors (FETs) in the presence of an electromagnetic pulse (EMP) are investigated in this paper. The numerical methodology employed is an efficient nonlinear finite-element method (FEM) that combines the element-by-element FEM and the preconditioned conjugate gradient technique. Parametric studies are carried out to show different pulse parameters on the transient thermal responses as well as maximum channel temperatures of some typical GaAs FETs, with silicon FETs also taken into account for comparison. It is numerically proven that the thermal impact caused by medium EMP will be the most serious compared with fast EMP or ultra-wideband pulse, and the captured maximum channel temperature is proportional to the input power density, approximately of the EMP injected. This research can serve as a base for taking further protection measures to prevent on-chip device from breakdown by the attack of an EMP.

Inversion mode n-channel GaAs field effect transistor with high-k/metal gate

Highly effective passivation of GaAs surface is achieved by a thin amorphous Si (a-Si) cap, deposited by plasma enhanced chemical vapor deposition method. Capacitance voltage measurements show that carrier accumulation or inversion layer is readily formed in response to an applied electrical field when GaAs is passivated with a-Si. High performance inversion mode n-channel GaAs metal-oxide-semiconductor field-effect transistors (MOSFETs) were fabricated with an a-Si/high-k/metal gate stack. Drain current in saturation region of 220mA∕mm with a mobility of 885cm2∕Vs were obtained at a gate overdrive voltage of 3.25V in MOSFETs with 5μm gate length.

Terahertz imaging with GaAs field-effect transistors

Imaging at 0.6 THz is tested with a commercial GaAs high-electron-mobility transistor (HEMT) operated at room temperature. The results allow the assessment of the potential of future antenna-fitted HEMT arrays for real-time imaging.

Reconfigurable Multiband Antenna Designs for Wireless Communication Devices

New designs for compact reconfigurable antennas are introduced for mobile communication devices. The uniqueness of the antenna designs are that they allow various groups of their operating frequency bands to be selected electronically. In particular, each group of frequency bands, or mode, can be made to serve several different communication systems simultaneously. These systems may include various combinations of GSM, DCS, PCS, UMTS, Bluetooth, and wireless local-area network (LAN). Therefore, by electronically selecting different antenna modes, a variety of communication systems can be conveniently served by only one antenna. One advantage is that through the different operational modes, the total antenna volume can be reused, and therefore the overall antenna can be made compact. In these designs, the selection of the different modes is achieved by either i) switching different feeding locations of the antenna (switched feed) or ii) switching or breaking of the antenna's connection to the ground (switched ground). This paper demonstrates these two designs. For the first design of switched feed, it can support GSM, DCS, PCS, and UMTS. In the second design, the antenna makes use of a switched-ground technique, which can cover GSM, DCS, PCS, UMTS, Bluetooth, and 2.4 GHz wireless LAN. The designs are investigated when ideal switches and also various realistic active switches based on PIN diodes, GaAs field effect transistor, and MEMs configurations. The designs are verified through both numerical simulations and measurement of an experimental prototype. The results confirm good performance of the two multiband reconfigurable antenna designs.

An Extension of the Classical Method to Design High Efficiency Microwave Class E PAs

This letter presents an extension of the analytical method proposed in (Mader and Popovic, 1995) to determine the impedance of the load network of a class E power amplifier (PA). The extended method lies in a new analytical expression for calculating the output load network, which allows for the parasitic elements and the time that the input signal takes for saturating the field effect transistor (FET). To demonstrate the usefulness of the extended method, two class E PA at 6 GHz, 4 V were designed and compared. One of them was designed using the classical method, while the second was designed using the extended method. Both amplifiers were fabricated on a Duroid substrate and the transistor used was a GaAs FET FLK057WG. The amplifier, designed with the extended method, exhibits an improvement on the power added efficiency of 18.6% in comparison with the amplifier designed using the classical theory.

Natural ageing effects of Schottky-gate GaAs FETs in current-voltage characteristics and in 1/f noise spectrum

We study the current-voltage (I–V ) characteristics and 1/f (flicker) noise spectra of experimental samples (prototypes) of submicron GaAs field-effect transistors (FETs) with Schottky planar gate in the linear regime. The model of I–V characteristics, in which the FET channel is described by the Shockley model and the crowding of current lines in passive regions is taken into account, is proposed. Analysis of the measured set of I–V characteristics allowed us to define geometric and electric parameters of the devices more precisely. The natural ageing effects were revealed by analyzing the measurements performed at a 3-year interval. We make the conjecture that excess defects are present in the structure and they are probably represented by dipoles (donor-acceptor pairs). Concentration of excess defects is estimated and its significant decrease with time is detected. For analysis of 1/f noise, we used the hypothesis of the existence of bistable point defects, assuming that the latter result in resistivity fluctuations of the conducting regions. It is shown that defects in the channel give the main contribution to 1/f noise and their concentration decreases with time. Increased content of defects near the buffer layer was detected in some devices. The experimental data obtained allow us to suppose that the observed 1/f noise is caused by the excess defects revealed in the analysis of I–V characteristics of FETs with Schottky planar gate.

A Distortion-Cancelled Doherty High-Power Amplifier Using 28-V GaAs Heterojunction FETs for W-CDMA Base Stations

An L/S-band 330-W distortion-cancelled Doherty GaAs field-effect transistor (FET) amplifier has been successfully developed optimizing the main and peak amplifiers load impedance shift. The amplifier employed a pair of 28-V operation 150-W GaAs heterojunction FETs. It demonstrated low third-order intermodulation of -37 dBc with a drain efficiency of 42% at an output power of 49 dBm around 6-dB backoff level under the two-carrier wideband code-division multiple-access (W-CDMA) signals of 2.135 and 2.145 GHz. To our knowledge, these represent the best results ever reported among the simple high-power FET amplifiers for W-CDMA base stations. In addition, we proposed the evaluation techniques to obtain each AM-AM and AM-PM characteristics of the main and peak amplifiers in an operating Doherty amplifier, and have experimentally proven the distortion cancellation effect in the GaAs FET Doherty amplifier

Nonactivated transport of strongly interacting two-dimensional holes in GaAs

We report on the transport measurements of two-dimensional holes in GaAs field-effect transistors with record low densities down to $7\ifmmode\times\else\texttimes\fi{}{10}^{8}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$. Remarkably, such a dilute system (with Fermi wavelength approaching $1\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$) exhibits a nonactivated conductivity that grows with temperature approximately as a power law at sufficiently low temperatures. We contrast it with the activated transport found in more disordered samples and discuss possible transport mechanisms in this strongly interacting regime.

Uncooled Infrared Detector Using a Thin InAsSb Layer Acting as a Gate on a GaAs Field-Effect Transistor

The demand for high-quality low-cost uncooled infrared (IR) photodetectors have significantly increased in recent years. In this paper, a novel concept of utilizing InAsSb as a midwave IR uncooled detector is introduced. According to the approach used in this paper, the InAsSb detection layer acts as gate over a GaAs field-effect transistor (FET). IR light is absorbed in the detection layer and changes the surface potential of the transistor. The current in the transistor, which is very sensitive to those changes, should yield a sensitive detector. The same concept can be generalized to other adsorbents that absorb light at the various range of the spectrum. The advantage of using the mature technology of GaAs for achieving a low-cost efficient uncooled IR detector is clear. The experimental results presented here, using InAsSb as the absorbing layer, serve as a proof of the general concept

Application of double camel-like gate structures for a GaAs field-effect transistor with extremely high potential barrier height and gate turn-on voltage

In this paper, extremely high potential barrier height and gate turn-on voltage in an n+/p+/n+/p+/n GaAs field-effect transistor employing double camel-like gate structures are demonstrated. The gate potential barrier height of the double camel-like gate is substantially enhanced by the addition of another n+/p+ layer in the gate region, as compared with the conventional n+/p+/n single camel-like gate structure. The influence of gate structure layers on the depletion depth, potential barrier height, transconductance and gate voltage swing are addressed. Experimental results show that a relatively high gate turn-on voltage up to +4.9 V is realized because two reverse-biased junctions of the double camel-like gate structures absorb part of the positive gate voltage. In addition, an extremely broad gate voltage swing greater than 4.6 V with the transconductance above 100 mS mm−1 is observed. These results indicate that the studied device is suitable for linear and signal amplifiers and inverter circuit applications.

PCSI 2006: Old problems and new visions

A brief review of the origin of the Conference on the Physics and Chemistry of Semiconductor Interfaces (PCSI) establishes a motivation—the need for an insulating material for GaAs field-effect transistors—for the resulting focus of PCSI on surface and interface issues that impact semiconductor devices. Highlights of past meetings emphasize the contributions and value of PCSI in promoting scientific advances in solid-state electronics. Turning to the future, motivation will again be established by identifying the wide spectrum of device concepts that offer great potential as the basis for future electronic, magnetic, and photonic technologies that will provide high-speed and low-power capabilities far exceeding present-day capabilities. Successful demonstrations of these nanoelectronics devices will only be possible if surface and interface issues are addressed at the earliest stages. In the future, PCSI will be dominated by many problems where nanostructures are fabricated and heterogeneous materials characterized and understood on scales measured in a few nanometers.

Effect of Oxidation using Ultraviolet Light and Ozone and Subsequent Nitridation using Electron Cyclotron Resonance Plasma on Gate Portion of GaAs Field-Effect Transistors

A recess-gate-type n-channel depletion mode metal–semiconductor field-effect transistor (MESFET), a metal–oxide–semiconductor field-effect transistor (MOSFET) prepared by UV and ozone oxidation, and metal–insulator–semiconductor field-effect transistors (MISFETs) prepared by oxidation followed by nitrogen plasma treatment for different time durations with an electron cyclotron resonance system (oxinitridation) were fabricated using an ex-situ process and equally current controlled recessed wafers. The MISFETs, especially the longest-nitrided one, showed the highest pinch-off gate voltage (-1.5 V) and the highest peak transconductance (170 mS/mm) at a 0.9 V gate voltage. The MOSFET showed the largest drain current, whereas the longest-nitrided MISFET showed the smallest drain current, owing to the difference in applicable forward gate voltage. These were clearly confirmed with statistical data. The transconductance obtained reproduces that of our previous experiment, and its increase is due to the improvement of crystallographic order in the vicinity of the insulator/semiconductor interface. The different applicable gate voltage implies that the subsequent nitridation weakens the barrier effect of the oxidized layer. An AlGaAs layer, as the mother material for oxinitridation, improves it.

Augmented hammerstein predistorter for linearization of broad-band wireless transmitters

In this paper, an augmented lookup-table-based Hammerstein predistorter is proposed for the first time in order to further improve the pre-correction capability of the traditional Hammerstein predistorter in the context of broad-band high-power wireless transmitters. The predistorter scheme consists of two separate modules, and its parameters are determined in two steps, which are: 1) static predistorter identification and then 2) dynamic part identification. The performance assessment of the newly proposed predistorter is carried out on a wireless transmitter prototype, which includes an L-band push-pull GaAs field-effect transistor 45-dBm peak-envelope power amplifier. Moreover, one- and three-carrier Third-Generation Partnership Projects frequency-division duplex wide-band code-division multiple-access signals are used as test signals to verify the robustness of this novel predistorter under different bandwidth signals. The linearized transmitter prototype output spectrum demonstrates noticeable superiority of the proposed augmented predistorter in suppressing the spectrum regrowth caused by the memory effects in comparison to the traditional Hammerstein predistorter.

Optical modulation of the effective channel thickness in GaAs field effect transistors with a Schottky gate (MESFETs)

Using a model relating the change in drain current with modulation of the effective channel thickness upon IR illumination of GaAs field effect transistors with a Schottky gate (MESFETs), it is shown that it is possible to determine the change in channel thickness and the concentration profile for deep centers in an FET channel. Profiles are given for the distribution of deep centers in the channels of GaAs MESFETs with different noise temperatures.

Microwave Characterization and Modeling of Packaged HEMTs by a Direct Extraction Procedure Down to 30 K

The knowledge of the small-signal equivalent circuit of microwave GaAs field effect transistors (FETs) is crucial for the design of low-noise amplifiers and is very useful to support the analysis of the transistor performance. This paper reports the results of our experimental activity concerning the application of an improved procedure for the direct extraction of the model element values from scattering (S-) parameter measurements. This analytical procedure was tested on low-noise pseudomorphic high electron mobility transistors (pHEMTs) up to 6 GHz and at cryogenic temperatures without any optimization or tuning adjustment. This paper reports the behavior of the intrinsic elements versus bias condition; the experimental results were found to match the theoretical expectations. The very good agreement between the simulated and measured S-parameters confirms the validity of the proposed method. To carry out the experimental activity, a properly designed cryogenic setup operating in our laboratory, which allows performing direct current (dc) and microwave characterization down to 30 K, was employed.

A novel GaAs FET with double camel-like gate structure

Extremely high potential barrier height and gate turn-on voltage of a novel GaAs field-effect transistor with n/sup +//p/sup +//n/sup +//p/sup +//n double camel-like gate structure are demonstrated. The maximum electric field and potential barrier height of the double camel-like gate are substantially enhanced by the addition of another n/sup +//p/sup +/ layers in gate region, as compared with the conventional n/sup +//p/sup +//n single camel-like gate. For a 1×100 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> device, a potential barrier height up to 2.741 V is obtained. Experimentally, a high gate turn-on voltage up to +4.9 V is achieved because two reverse-biased junctions of the double camel-like gate absorb part of positive gate voltage. In addition, the transistor action shows a maximum saturation current of 730 mA/mm and an extrinsic transconductance of 166 mS/mm.

Ionization-induced carrier transport in InAlAs/InGaAs high electron mobility transistors

Time resolved charge-collection measurements and two-dimensional device simulations performed on InAlAs/InGaAs high electron mobility transistors (HEMTs) for ion and pulsed laser excitation address the mechanisms of charge collection and enhancement in these heterostructure devices. The results are compared to those for bulk GaAs field-effect transistors. In the HEMTs, the ionization-induced enhancement current is associated with a significant lowering of the source/channel barrier, and is largely confined to the InGaAs well. The simulations suggest that the primary contributor to the barrier lowering is an excess hole density that develops in the InAlAs buffer layer.