A simple and efficient method of GaAs FET amplifier analysis is presented. The FET is represented by its circuit-type nonlinear dynamic model taking into account the device's main nonlinear effects including gate-drain voltage breakdown. An identification procedure for extraction of the model parameters is described in detail and examples are given. The calculation of the amplifier response to a single-input harmonic signal is performed using the piecewise harmonic balance technique. As this technique is rather time-consuming in its original form, the optimization routine used to solve the network equations was replaced by the Newton-Raphson algorithm. Characteristics calculated with the use of the proposed method are compared with experimental data taken for a microwave amplifier using a 2SK273 GaAs FET unit. Good agreement at 9.5 GHz over wide ranges of bias voltage and input power levels are observed.

Computer Calculation of Large-Signal GaAs FET Amplifier Characteristics

A method to measure impact ionization current in GaAs MESFETs is presented. The impact ionization current is then used to calculate the maximum electric field in the channel and the impact ionization coefficient. Data for the electron impact ionization coefficient in [110] GaAs are extended beyond previous studies by five orders of magnitude. Impact ionization is taken into account in a new gate current model. >

Impact ionization in GaAs MESFETs

Two dimensional computer simulation of the GaAs MESFET in the presence of a uniform surface charge predicted initial gate-drain avalanche voltages at variance with experiment in two respects: (a) The dependence of initial avalanche voltage upon gate length was weak compared with that evident in practice. (b) The absolute values of voltage were smaller by a factor of typically 3 than those observed experimentally. Examination of the potential and charge distributions revealed, even at low gate-drain potentials, electric fields near the drain end of the gate of sufficient magnitude to cause field emission. Electrons emitted in a direction parallel to the GaAs surface may occupy states in the forbidden band, which would result in a dynamic excess of charge residing on the surface immediately adjacent to the drain end of the gate. Inclusion of this effect in the computer model resulted in a simulated device behavior which is now similar to that found in practice.

The role of the device surface in the high voltage behaviour of the GaAs MESFET

The surface potential effect on gate-drain avalanche breakdown in GaAs MESFET's is investigated with a two-dimensional device simulator. It is shown that the surface potential effect changes the potential distribution in GaAs MESFET's drastically and therefore plays an important role in determining drain breakdown voltage. In addition, two device structures producing high breakdown voltages, an offset gate structure and a recessed gate structure, are analyzed.

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Surface potential effect on gate&#8212;Drain avalanche breakdown in GaAs MESFET's

This communication describes a detailed experimental investigation of light emitted from AlGaAs/GaAs high electron mobility transistors biased at high drain voltages where impact ionization occurs. We present the electroluminescence spectra in 1.1–3.1 eV energy range. The strong correlation of the integrated intensity of photons with hν≳1.7 eV with the product of hole current generated by impact ionization and of electron current indicates that the recombination process is the main mechanism for visible light emission.

Impact ionization, recombination, and visible light emission in AlGaAs/GaAs high electron mobility transistorsa)

The voltage breakdown behavior of a number of different MESFET structures has been investigated using a two-dimensional numerical model. The site of the avalanche is found to be under the drain edge of the gate in recessed devices under all bias conditions, but moves towards the drain contact in planar structures when the channel is not pinched off. The dependence of the breakdown voltage on a variety of geometrical and physical variables has been studied. In particular the surface is shown to play an important part in determining the breakdown voltage.

J.E. Sitch

Papers

Gate-drain avalanche breakdown in GaAs power MESFET's