Analysis of semiconductors with field-dependent mobility
Using the time domain analysis of Lagrangian approach, the small-signal behavior of a semiconductor with field-dependent mobility under various contact conditions is analyzed. A generalized closed form solution for an impulse current response is derived when the carrier velocity characteristic is expressed by a piecewise linear function. This result gives an accurate description of the transient performance of the device and can provide good insight into device operation. Numerical examples are given for a negative differential mobility GaAs crystal, considering the conditions under which negative resistances occur. A generalized small-signal impedance of the semiconductor is given, from which previous results reported for particular devices can be obtained as special cases.
Computer simulation of InP transferred-electron amplifiers for Ka-band
A displaced Maxwellian approach which includes relaxation effects is used to simulate small- and large-signal InP transferred-electron amplifiers operating inKa-band. The devices considered are short-circuit stable; that is, they have a subcritical doping-length product. The performance of amplifiers having the usual n+-cathode contacts, and p-type notch-cathode contacts designed to produce a uniform electric field, are compared. It is found that the notch contacts have a moderate influence on small-signal characteristics, and a profound influence on large-signal performance. Small-signal bandwidths of 65 percent are predicted for both types of contacts. The saturation efficiency of amplifiers, biased at three times threshold, is much higher for the notch-contact device with values near 5 percent being predicted. The nonlinearity of the large-signal gain characteristic is shown to vary greatly as the frequency deviates from the optimum value.
Some properties of the moving high-field domain in Gunn effect devices
Some experimentally observed characteristics of the high-field domain in long samples (0.1 to 0.25 cm) of GaAs are described. Accurate determinations of domain velocity and amplitude in a number of devices have been made using a surface potential probe. Although the probe resolution was insufficient to observe the domain widening as it supports more voltage, as is predicted by the Ridley model, it has been shown that domain fields in excess of 75 kV/cm exist in long samples. In presenting the results it has been convenient to recognise two classes of behaviour: (1) Samples showing only small departures from the Ridley model and good waveform coherence; these have been termed 'well behaved;' and (2) samples in which additional perturbing processes modify the Gunn effect. Of the two such processes studied, namely, that giving rise to the emission of recombination radiation from the moving domain, and, secondly, electron traping within the domain, the former is by far the most important since, depending on sample length and carrier concentration, it will always occur at sufficiently high applied fields. From considerations of the space-charge distribution necessary to support the high domain fields a model has been developed, the chief feature of which is a triangular domain field distribution. The peak value of the domain field is dependent on the domain voltage drop and the material carrier concentration. The model explains most of the experimental observations and, in particulars the factors which determine whether a sample is well behaved or emits recombination radiation. In addition, the model gives a semiquantitative picture of the primary current-field characteristics of the transferred electron mechanism.