G. Salmer

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

Noise modeling in TEGFETs 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 TEGFETs and MESFETs is carried out. A new method for calculating the noise and gain performances of FETs is then proposed.

Theoretical contribution to the design of millimeter-wave TEO's

Systematic simulations of GaAs millimeter-wave transferred-electron devices have been performed, using a realistic model taking into account spatial nonuniformity as well as relaxation effects. Operating temperature is also considered. These simulations indicate the possibility of a fundamental accumulation layer transit mode up to 100 GHz, with higher conversion efficiency than that obtained with a harmonic mode. Significant improvement in output power is expected from InP fundamental oscillators in the upper part of the millimeter band.

MODFET 2-D hydrodynamic energy modeling: optimization of subquarter-micron-gate structures

Using a two-dimensional hydrodynamic energy model incorporating nonstationary electron dynamics and nonisothermal electron transport (which characterizes submicron-gate MODFETs), the main physical phenomena that govern the device performance at 300 K are highlighted. This covers velocity overshoot effects, stationary-domain formation, and real space transfer. The model is then used systematically to predict the precise values of the small-signal parameters for different bias conditions. The potential performance improvement achieved by reducing the gate length below 0.2 mu m is investigated. It is shown that improvement in transconductance is achieved through gate-length reduction if a severe restriction on the aspect ratio is respected. >

Two-dimensional simulation of submicrometer GaAs MESFETs: surface effects and optimization of recessed gate structures

The surface potential effect in GaAs MESFETs causes a depleted zone to form not only between the source and gate, but also between the gate and drain. The consequences of this phenomenon on the device behavior, the DC and AC characteristics, and the expected performance are studied. For this purpose, a two-dimensional resolution of the basic semiconductor equations is used. This model takes into account relaxation effects by including an energy relaxation equation. The dependence of MESFET characteristics such as transconductance, output conductance, and capacitance on the dimensions of the zone where surface potential effects occur is given. Some interesting conclusions concerning the optimization of recessed-gate structures are drawn. >

Performance analysis of sub-micron gate GaAs MESFETs

Abstract A novel 2-D numerical model incorporating nonstationary electron dynamics is used to investigate the complex transport phenomena governing the operation of sub-micron gate GaAs MESFETs. A detailed theoretical analysis of different phenomena observed in subhalf micron devices is given. These include velocity overshoot, stationary and travelling domain formation, soft pinch off, excess drain current etc. The small signal parameters g m , g d and C gs and their dependence on bias condition are evaluated. The effects of physical quantities such as mobility and interface barrier on carrier injection and transport and consequently on device performance are presented.

Experimental analysis of HEMT behavior under low-temperature conditions

An experimental analysis of high-electron-mobility transistor (HEMT) behavior under low-temperature conditions is presented. Specific measurements have been performed to investigate the deep-level trapping effects on basic device characteristics such as carrier concentration, electron mobility in the structure, and access resistances. The influence of the collapse phenomenon on the microwave device parameters completes the knowledge of these parasitic effects. Explanation of mechanisms responsible for the anomalous phenomena and means to suppress them are reported. Microwave parameters measurements demonstrate that HEMTs showing no parasitic collapse effects exhibit improved performance at 77 K. Large improvements of current gain cutoff frequency and noise figure are presented. >

2-D simulation of degenerate hot electron transport in MODFETs including DX center trapping

A comprehensive 2-D hydrodynamic energy model which is capable of describing nonstationary electron dynamics and nonisothermal transport within submicrometer MODFETs (TEGFETs or HEMTs) is presented. The model accounts for carrier degeneracy, deep DX center levels, and conduction outside the quantum well, thereby including bulk and parasitic MESFET effects. A technique for handling carrier degeneracy is presented. The authors also present two techniques developed to overcome the complexity of solving the coupling between the model nonlinear partial differential equations (PDEs). These cover DX center trapping kinetics and the energy derivatives in the Jacobian, particularly regarding the energy-conservation equation. The model is so informative that it highlights the main physical phenomena which govern device behavior such as velocity overshoots, stationary domain formation, buffer injection, back injection, and local longitudinal field inversion at the gate entrance of the channel. The model is systematically used to predict the DC and small-signal performance of submicrometer gate AlGaAs-GaAs MODFETs operating at room temperature. >

Fundamental limitations of the Controlled Avalanche Transit Time transistor (CATT)

Abstract This paper reviews the fundamental limitations of the CATT as a high power and high frequency device. The 1st section recalls CATTs principles. The 2nd section gives preliminary studies showing the device limitations under d.c. operating conditions. Then, the 3rd and 4th sections present a thorough analysis and a numerical simulation allowing us to show the more important of CATTs limitations under microwave class B or C operating conditions. Finally, the 5th section concludes this study with experimental verifications of the theoritical predictions.

Structural optimization of millimeter-wave subhalf-micron gate MODFETs

A study of the variations of the small signal parameters of subhalf-micron-gate Het-erostructure Field Effect Transistors HFETs with device scaling (aspect ratio), gate offset in the recessed zone and hot-carrier confinement by buffer barriers is carried out for the sake of optimizing sumicron HFET structures for 40–100 GHz applications. We discuss the performance limits of existing structures and investigate new concepts and approaches to circumvent these limitations based on thorough understanding of device physics gained from 2D energy modeling. We project a net improvement in HFET millimetric performance using subhalf-micron-gate pseudomorphic structures which we expect to have maximum oscillation frequencies in excess of 400 GHz in the near future.

Noise in two dimensional electron gas field effect transistor

Abstract A theoretical model of the noise properties of TEGFETs is described. Taking the particularities of this structure into account, this model gives results in good agreement with Experiments and allows us to investigate the influence of the main technological parameters.