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.
Tissue Characterization by Ultrasonic Impediography
An analytical method is presented which can be utilized for tissue characterization. This method permits the simultaneous determination of the attenuation and the impedance profiles. Higher-order reflections are included in the formulation. Computer simulated results for a hypothetical case are included.
Small-signal behavior of Gunn diodes
Calculations of small-signal impedance have been made for Gunn diodes over a broad range of length and bias current density, taking into account the spatial inhomogeneity of the dc electric field. The nature of the impedance functions was found to vary with the above parameters, and was distinctly different for amplifying diodes, oscillatory diodes, and diodes biased below the threshold for active behavior. Nyquist stability analysis was used to relate the impedance behavior to the effects of circuit and bias level on oscillatory and amplifying behavior. The results of this analysis are found to be in good agreement with the experimental observations of other authors.