The Nonlinearity of the Reverse Current-Voltage Characteristics of a p-n Junction Near Avalanche Breakdown

For nonlinear applications such as high-speed switching, a device figure of merit is 7, the ratio of the second derivative to the first derivative of the current-voltage (.I-V) characteristic, or 7 = ( d 2 I / d V 2 ) / ( d I / d V ) . At room temperature, the value of 7 for an ideal forward-bias Schottky diode is about 40 V~l. It is shown that although the ideal reverse breakdown characteristic could give a value of 7 greater than J+0 V - 1 , because of the statistical distribution of impurities, the effect of space-charge resistance, and other complications, much lower values of 7 are expected. Furthermore, the nonlinear characteristic is noisy, relatively slow, and causes some power consumption. It appears, therefore, that this nonlinearity is not likely to supersede Schottky barrier diodes in high-speed switching applications. It does not, however, ride out the possibility of microwave generation application. F o r nonlinear applications such as high-speed switching, a device figure of merit is y, the ratio of the second derivative to t h e first derivative of the current-voltage characteristic. T h e value of y is a measure of the degree of nonlinearity, normalized to t h e operating admittance level. It is used here to compare the nonlinearity of a reverse-biased diode near breakdown to t h a t of a forward-biased p-n junction or a Schottky barrier. T h e current-voltage characteristic and y for a forward-biased p-n junction or a Schottky barrier are given by I = I0[e"r/nkT - 1] 7 (d2I/dV2)/(dI/dV) 1135 (1) = (2)