Small-signal analysis of the Read avalanche diode

A small-signal analysis is made on the Read-type avalanche transit time diode in which both holes and electrons and differing ionization rates for holes and electrons are considered in a silicon diode. The avalanche region is assumed to be an unsymmetric abrupt junction in which the ionization coefficients vary with the distance through their exponential dependence on the field in the avalanche region. Solutions for the ionization integral are given in the dc case. The time-varying terms are introduced as small-signal perturbations on the dc case and solutions for the ionization integral are again obtained and expressed as a Fourier series. The coefficients of the series appear in the expressions for the admittance. This approach provides simple analytical solutions for the Read diode admittance. Also, direct evaluation of the Fourier coefficients is given in terms of the diode's breakdown voltage and other known parameters. An equivalent circuit for the Read diode is developed. Over a substantial frequency but for small transit angles of the drift region, it consists of a frequency independent negative conductance, inductance, and capacitance. The diode's spreading resistance is in series with these parallel elements. The circuit agrees with the measurements of Josenhans and Misawa. On the basis of the small-signal avalanche analysis the ultimate oscillator efficiency is estimated to be about 26 percent.