The lateral p-n-p transistor—A practical investigation of the DC characteristics

The dc characteristics of the lateral p-n-p transistor are investigated with the goal of providing an uncomplicated but accurate description that considers the practical needs of the device and circuit designer. An experimental step-by-step analysis of collector- and base-current components shows that a one-dimensional model describes the device adequately. The model parameters are closely related to process parameters and device geometry allowing quick assessments of layouts and processes. In particular, a comparison of various emitter geometries is given, showing among other facts the adverse effect of unnecessarily large emitter contact holes. Of the mechanisms determining the base current, volume and surface recombination in the intrinsic base were found to be insignificant. Instead, an additional component, the vertical diffusion of holes out of the intrinsic base, has been experimentally verified. The main contribution to base current, however, is the current across the emitter bottom junction. High-level injection is considered in the collector current by using a modification of Chou´s equations. Gummel-Poon knee voltages have been determined for various dopings and basewidths. Our experiments show that the knee voltage depends on basewidth, which goes beyond Chou´s description.