INVESTIGATION OF CURRENT-GAIN TEMPERATURE DEPENDENCE IN SILICON TRANSISTORS

This paper presents the results of an investigation of the factors influencing transistor current-gain temperature dependence. Phase one of the investigation demonstrated experimentally that current-gain temperature dependence is an inverse log function of the average active base resistivity. Devices were found to be less temperature sensitive with lighter base doping levels. Phase two of the investigation experimentally demonstrated current-gain temperature dependence to be an inverse exponential function of the emitter doping level. This large temperature dependence is shown to be a possible consequence of an emitter band-gap decrease, presumably caused by the large number of dislocations and lattice deformations at high doping levels. Using the predicted techniques, several runs of epitaxial planar devices were fabricated which had practically no current-gain temperature dependence, and suffered no noticeable loss in other parameters. Current-gain temperature dependence is also thought to be one of the contributors to hot-spot formation and secondary breakdown. To determine if secondary-breakdown capability had been increased, these temperature-insensitive devices were tested to forward secondary breakdown and compared to standard products of the same geometry. The temperature-independent devices were able to withstand a 40-percent increase in operating power before the onset of secondary breakdown. This increase in capability is thought to be the result of less tendency toward hot-spot formation due to decreased thermal regenerative action. Copyright © 1969 by The Institute of Electrical and Electronics Engineers, Inc.