Conventional MODFET Research Articles

Comparative study on performance of cubic AlxGa1−xN/GaN nanostructures MODFETs and MOS-MODFETs

We report some comparative results on cubic AlxGa1−xN/GaN nanostructures MODFET and MOS-MODFET. The drain current characteristics of cubic AlxGa1−xN/GaN MODFET and MOS-MODFET are simulated by changing the different device parameters such as Al content x and the cubic GaN buffer layer thickness using 2D nextnano3 numerical simulation software. Drift–diffusion model has taken for simulating the proposed device. These results clearly indicate that the transistor simulation with 5nm isolator SiO2 layer thickness under the gate, Al content of x=25% and 200nm cubic GaN buffer layer thickness shows the tremendous I–V characteristics. Also, this structure shows an increase of the drain saturation current and a decrease in the threshold voltage. Moreover, our simulation results exhibited lower threshold voltage and higher drain current density of MOS-MODFET is a factor 30% higher than the same current of a conventional MODFET. The MODFET with 5nm isolator SiO2 layer thickness has been much better performance. To avoid current flow through the high conductive 3C-SiC substrate a 150nm p-doped cubic GaN layer is deposited. A comparison between our experimental and simulation results are shown to be in good agreement for cubic Al0.25Ga0.75N/GaN nanostructures MOS-MODFET. The demonstrated MOS-MODFET will be attractive for the next-generation microwave and high power switching application fields.

Analytic solution of the velocity-saturated MOSFET/MODFET wave equation and its application to the prediction of the microwave characteristics of MODFETs

An AC model for the saturated MODFET is reported. The MOSFET/MODFET wave equation accounting for velocity saturation and channel length modulation is derived. An exact solution of the wave equation is obtained in terms of Bessel functions. A frequency power series is used to derive analytic expressions for the intrinsic Y-parameters. This AC model is applied to the prediction of the microwave characteristics of 1- mu m AlGaAs/GaAs MODFETs and GaAlAs/InGaAs/GaAs pseudomorphic MODFETs. The parameters used by the AC model are extracted by fitting the I-V characteristics. The parasitics are either estimated or measured. A good prediction of the scattering parameters measured from 2 to 18.4 GHz is achieved for different biases. The deviation of the calculated unilateral power gain from the measured values was on average 1.25 and 2.18 dB for the conventional MODFET and the pseudomorphic MODFET, respectively. >

Quantum interference devices fabricated using molecular-beam epitaxy and ultra-high-resolution electron-beam lithography

Summary form only given. The authors have fabricated various new lateral quantum interference devices (QIDs) using molecular-beam epitaxy and ultra-high-resolution electron-beam lithography and have observed conductance oscillations in these devices. These QIDs have a structure which is similar to that of a conventional MODFET, except for the gate(s), which consists of various nanometer patterns instead of a plain gate. The gate nanometer patterns create electrostatic potential barriers and well(s) in the channel. At low temperatures, as the electron mean-free path approaches or becomes longer than the gate length, quantum interference of the electron wave with the barriers and wells results in the formation of quasi-bound states or subbands, and, as a result, the conductance oscillates as either the gate voltage or the source-drain voltage is scanned. Several novel QIDs are presented with emphasis on a new lateral quantum box transistor (LQBFET), which has a railway track gate. >

The submicron inverted MODFET I-GaAs/N +-AlGaAs: a 2D Monte-Carlo study

A two-dimensional Monte-Carlo simulation of an inverted MODFET structure I-GaAs/N +-AlGaAs has been performed. The influence of various technological parameters have been studied such as the GaAs undoped layer thickness, the AlGaAs layer thickness, doping level and aluminum composition, the gate length or the temperature. The results show that higher transconductance and cut-off frequency values should be obtained as compared to conventional MODFET structures.

Design of enhanced Schottky-barrier AlGaAs/GaAs MODFET's using highly doped p+surface layers

The design and performance of enhanced Schottky-barrier height modulation-doped AlGaAs/GaAs field-effect transistors (ESMODFET's) is discussed. Results are presented showing that the addition of a thin highly doped p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> layer under the gate can increase the forward biased gate turn-on voltage from 0.8 V (conventional MODFET) to as high as 1.6 V. A mathematical model is presented that predicts the thickness and doping of the heterostructure layers required to obtain a given threshold voltage and effective Schottky-barrier height. It is predicted that this enhanced Schottky barrier will allow increased gate-voltage swings and thus significantly improve the noise margin of enhancement-mode MODFET circuits.

Pseudomorphic InGaAs/AlGaAs modulation-doped FET's with reduced low-frequency noise and thermally stable performance

A high-performance MODFET structure grown by MBE with the incorporation of a single quantum well In 0.15Ga 0.85As layer for the transport of 2D electron gas has been critically examined for its thermal stability at 80 K and low-frequency noise from 10 -2 to 10 8 Hz. Experimental results indicate that the behavior of this device in both these respects is much superior when compared with the same behavior of conventional MODFET's. A maximum low-field carrier mobility of 29,000 cm 2/s at 80 K and an average carrier saturation velocity of 2×10 7 cm/s at 300 K in a 1 μm gate device clearly indicate that the quality of the pseudomorphic quantum well (InGaAs) layer is either comparable or better than that of the usual GaAs buffer layer. The deep level spectra, obtained through photo-FET measurements, and the low-frequency noise spectra at different temperatures obtained for the new pseudomorphic and conventional MODFET's have clearly indicated that contributions from various deep levels present in the new structure are significantly reduced.

Low-noise behavior of InGaAs quantum-well-structured modulation-doped FET's from 10-2to 108Hz

Equivalent gate noise voltage spectra of 1-µm gate-length modulation-doped FET's with pseudomorphic InGaAs quantum-well structure have been measured for the frequency range of 0.01 Hz to 100 MHz and compared with the noise spectra of conventional AlGaAs/ GaAs MODFET's and GaAs MESFET's. The prominent generation-recombination (g-r) noise bulge commonly observed in the vicinity of 10 kHz in conventional MODFET's at 300 K does not appear in the case of the new InGaAs quantum-well MODFET. Instead, its noise spectra indicate the presence of low-intensity multiple g-r noise components superimposed on a reduced 1/f noise. The LF noise intensity in the new device appears to be the lowest among those we have observed in any MODFET or MESFET. The noise spectra at 82 K in the new device represent nearly true 1/f noise. This unusual low-noise behavior of the new structure suggests the effectiveness of electron confinement in the quantum well that significantly reduces electron trapping in the n-AlGaAs, and thus eliminates the g-r noise bulge observed in conventional MODFET's.

STABILITY OF SI-DOPED AlGaAs/GaAs MODFET STRUCTURES DURING CONVENTIONAL FURNACE AND RAPID OPTICAL ANNEALING.

AbstractThe use of an AlGaAs/n-GaAs superlattice in place of the n-AlGaAs layer in MODFET devices reduces the light and temperature sensitivity of the threshold voltage. This paper considers the stability of Si doped superlattices under annealing conditions required for activation of the implant in the self-aligned gate MODFET fabrication process. Rapid optical annealing does not significantly degrade the superlattice structure. The DX center concentration in the superlattice structures is a factor of 30 less than measured in conventional MODFET structures. High performance MOOFET devices have been fabricated using the self-aligned gate process with rapid optical annealing.