Two-dimensional Electron Gas Field-effect Transistors Research Articles

Compensation for the Nonlinearity of the Drain–Gate I–V Characteristic in Field-Effect Transistors with a Gate Length of ~100 nm

The nonlinearity of the gate–drain current–voltage characteristics in classical Schottky transistors and two-dimensional electron gas field-effect transistors based on AlGaAs/InGaAs/GaAs and InGaAs/GaAs compounds is analyzed. The carrier velocity-overshoot effect in the transistor channel is analyzed for various doping profiles of the structures under study.

Компенсация нелинейности сток-затворной вольт-амперной характеристики в полевых транзисторах с длиной затвора ~100 нм

Abstract The nonlinearity of the gate–drain current–voltage characteristics in classical Schottky transistors and two-dimensional electron gas field-effect transistors based on AlGaAs/InGaAs/GaAs and InGaAs/GaAs compounds is analyzed. The carrier velocity-overshoot effect in the transistor channel is analyzed for various doping profiles of the structures under study.

The passivation/modification of AlGaAs/GaAs surfaces by amorphous TiO 2 for the bio-sensing use in electrolytes

In order to apply two-dimensional electron-gas field effect transistors (2DEG-FETs) for bio-sensing devices operating in electrolytes, the chemical/electrical properties of TiO 2 thin film is investigated as a material for the gate oxide of FETs. TiO 2 films of thickness 13–15 nm are prepared with sol–gel technique on the gate surfaces of AlGaAs/GaAs 2DEG-FETs, followed by heat treatment at 450 °C. The TiO 2 surface has nanometer-scale roughness with a peak-to-peak height difference of approximately 10 nm. The TiO 2/2DEG-FETs exhibit a good performance for operation in electrolytes in the dark, with a transconductance of 0.20 mA/V. Large and continuous threshold shifts to the negative side of V gs are resulted when the TiO 2/2DEG-FETs are operated under light at negative gate biases ( V gs < 0 V). This reveals that photoexcited holes are accumulated at the interface of TiO 2/GaAs by the negative gate biases. The sensitivity for pH and H 2O 2 is examined for the TiO 2/2DEG-FETs, where a sensitivity of 71 mV/pH and a finite response for H 2O 2 are obtained. Cell culture on TiO 2 surfaces is successfully demonstrated, showing a high potential of the TiO 2/2DEG-FETs for cell activity sensors.

Wide-band transimpedance amplifiers using AlGaAs/In/sub x/Ga/sub 1-x/As pseudomorphic 2-DEG FET's

Monolithic wide-band amplifiers have been demonstrated using AlGaAs/In/sub x/Ga/sub 1-x/As/GaAs pseudomorphic two-dimensional electron-gas field-effect transistors. The amplifiers have yielded an 18.0 GHz bandwidth and a 41.8 dB/spl Omega/ transimpedance gain with a feedback resistance of 100 /spl Omega/. In addition, the dependence of In mole fraction for an In/sub x/Ga/sub 1-x/As channel layer on device and amplifier performance has been also investigated. The g/sub m/ and the f/sub T/ in a device, along with the bandwidth, the gain, and the noise performance in an amplifier, have improved as the In mole fraction is varied from 0 to 0.25.

Single electron effect transistor: Fabrication and observation

Single Electron Effect Transistors (SEET) based on the Coulomb blockade effect, have been fabricated in a TEGFET (Two-dimensional Electron Gas Field Effect Transistors) like configuration which involves a small 2D (Two dimensional) electron gas island obtained by Schottky gates. At low temperature these devices demonstrate clearly the periodic conductance oscillations when the electron number in the island increases or decreases monotonously, non-linear I-V relation when the system is selected at a blocked state, and linear I-V relation for a conducting state.

Ga0.51In0.49P/GaxIn1-xAs lattice-matched (x=1) and strained (x=0.85) two-dimensional electron gas field-effect transistors

The authors report the fabrication of n-type GaInP/GaxIn1-xAs lattice-matched (x=1) and strained (x=0.85) two-dimensional gas field-effect transistors grown by low-pressure metallorganic chemical vapour deposition on GaAs semi-insulating substrates. The GaAs-GaInP devices demonstrate excellent operational performance at low temperature, due to the absence of deep traps in doped GaInP layers. The extrinsic transconductance is 163 mS mm-1 at 300 K and 213 mS mm-1 at 77 K. The threshold voltage of the devices biased in the dark at Vds=3 V was -3.34 V at 300 K and -3.38 at 77 K. Microwave measurements revealed cut-off frequencies fT of 17.8 GHz and fMAX of 23.5 GHz.

DC and RF characteristics of InAlAs/InGaAs dual-gate TEGFETs

DC and microwave measurements on 0.7 μm single-gate (SG) and dual-gate (DG) In0.52Al0.48As/In0.53Ga0.47As planar doped two-dimensional electron gas field-effect transistors (TEGFETs) are reported. The DG devices show a large increase of the gm to gD ratios, which are as high as 100 at gm = 380mS/mm, compared with 12 at 420mS/mm for the single gate (SG) devices on the same chip, as well as 6dB improvement in the RF power gain compared with their SG counterparts.

DC, small-signal, and noise modeling for two-dimensional electron gas field-effect transistors based on accurate charge-control characteristics

A practical model for DC, small-signal, and noise characteristics in two-dimensional electron gas field-effect transistors is discussed. The model includes accurate charge-control characteristics based on analytical functions relating carrier concentration to Fermi level. This model allows the influence of drain current, frequency, and device parameters on the noise figure (NF) to be studied. The theory explains the experimentally observed trend in NF behaviors.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Accurate modeling for parasitic source resistance in two-dimensional electron gas field-effect transistors

An accurate two-layer model has been developed for parasitic source resistance in two-dimensional electron gas field-effect transistors (2DEGFETs). In this model, the 2DEG concentration-voltage and current density-voltage relations at the cap/barrier/2DEG junction are taken into account, based on the self-consistent charge control model and effective mass tunneling theory. Empirical 2DEG velocity field characteristics are also included. To show the feasibility of this method, the source resistance in conventional GaAs/AlGaAs 2DEGFETs was analyzed and the AlGaAs thickness dependence was discussed. For comparison, the lattice-matched GaInAs/AlInAs 2DEGFET and pseudomorphic GaInAs/AlGaAs 2DEGFET were examined. It was shown that introducing a highly doped cap layer leads to a drastic reduction in source resistance for pseudomorphic 2DEGFETs but has a very small effect for GaInAs/AlGaAs 2DEGFETs. >

Analysis of charge control in pseudomorphic two-dimensional electron gas field-effect transistors

An exact model for charge control in two-dimensional field-effect transistors (2DEGFETs) is discussed. The model is based on a first-principles theory, in which self-consistent quantum two-dimensional electron subbands and numerical solutions of Poisson's equation for band bending, space charge, and three-dimensional holes are included. The charge control in InGaAs/AlGaAs pseudomorphic 2DEGFETs is analyzed and compared with that in the GaAs/AlGaAs conventional 2DEGFET. It is shown that a quantum-well channel in the pseudomorphic 2DEGFET can achieve high carrier confinement as well as high carrier concentration. From the calculated gate capacitance-voltage behavior, a simple estimation for the device performance is obtained. The results indicate that the pseudomorphic 2DEGFET with a large conduction band discontinuity at the channel interface can improve transconductance-gate voltage characteristics, and thus maximum transconductance, and the cutoff frequency-gate voltage characteristics. >

Molecular-beam epitaxial growth and characterization of strained GaInAs/AlInAs and InAs/GaAs quantum well two-dimensional electron gas field-effect transistors

Defect free strained layer epitaxy opens possibilities for further improvement on the quantum well two-dimensional electron gas (TEG) structures grown using the GaInAs/AlInAs on InP materials system. Increased freedom with composition allows for optimizing certain properties of the structure, such as, the conduction edge discontinuity which controls the maximum sheet concentration (ns); and the electron effective mass which influences the speed of the structure. These enhancements can be made, respectively, by increasing the Al concentration in the AlInAs and/or by decreasing the Ga concentration in the GaInAs. The maximum amount of strain which can be incorporated into the unrelaxed material sets an upper limit on the compositional tolerances. The tolerances will be shown to be large for the AlInAs and the active TEG GaInAs region. The compositions are obtained using the intensity oscillations observed in the reflective high-energy electron diffraction (RHEED) specular beam during growth of GaAs, AlAs, and subsequently GaInAs and AlInAs on GaAs. X-ray rocking curves and photoluminescence (PL) are used to verify the calibrations for growths on InP. The dependency of the mobility on strain is shown. The maximum 300 K mobility obtained was 12 360 cm2/V s, with ns of 1.25×1012/cm2. The well thickness was 84 nm. The AlInAs and GaInAs were estimated to be +0.04 and +0.17 In mole fraction from lattice match, respectively. A mobility of 11 550 cm2/V s was obtained using a 34-nm well. InAs/GaAs superlattice quantum well TEG structures were grown and characterized. TEG field-effect transistors performance comparable to standard structures were obtained in preliminary layers. Exceptionally high Si doping levels roughly 20 times the maximum obtained with Al0.25Ga0.75As have been achieved with lattice matched AlInAs.

Noise modeling in submicrometer-gate two-dimensional electron-gas field-effect transistors

Noise modeling in TEGFET's which provides good results in agreement with the experimental findings is presented. The influence of the main technological parameters on the noise figure and associated gain is given for operating frequencies up to 60 GHz. A comparison between TEGFET's and MESFET's is carried out. A new method for calculating the noise and gain performances of FET's is then proposed.

Ultra low noise and high frequency operation of TEGFETS made by MBE

Microwave characteristics of two dimensional electron gas field effect transistors (TEGFETS) have been evaluated for low noise applications. At 17.5 GHz, a noise figure of 1.4 dB with an associated gain of 9 dB and a maximum available gain of 11.5 dB was obtained at drain current of 6 mA. These results are comparable to the best performances reported so far.

Abrupt OMVPE grown GaAs/GaAlAs heterojunctions

In this paper, we describe the growth of abrupt heterojunctions and very thin GaAs and GaAlAs layers for use in quantum well lasers or TEGFET (two-dimensional electron-gas field effect transistors) structures. SIMS measurements have been performed which confirm that the growth rate measured for thick layers (1 to 10 μm) can be used to estimate the thickness of very thin layers (<100 Å) with a good accuracy. Luminescence data from GaAlAs/GaAs/GaAlAs quantum wells shows that there is probably some random compositional fluctuation in the GaAlAs quantum well barrier layers which leads to a broadening of the luminescence peak and a shift to lower energy. These quantum wells form the active layer of separate confinement heterostructure (SCH) and graded refractive index (GRIN) SCH quantum well laser structures. We will review the results of our study of these lasers explaining the separate roles of the GRIN and quantum well. New results will be given showing how the value of T 0 can be improved by increasing, the number of quantum wells in the active layer.

Low noise normally on and normally off two-dimensional electron gas field-effect transistors

Normally on and normally off two-dimensional electron gas field-effect transistors (TEGFET’s) have been fabricated. Source, drain, and gate are directly deposited on the Si-doped AlGaAs top layer without any recess. At 10 GHz noise figure is 2.3 dB for both types with an associated gain of 10.3 and 7.7 dB for normally on and normally off device respectively. High performance normally off TEGFET opens a large field of application.