Temperature rise of solid junctions

SEMICONDUCTOR DEVICES always contain a junction; i.e., a plane zone of vanishing thickness. Current pulses through the device generate heat, mostly in the zone, from which it diffuses into the adjoining metallic body. Heat causes an increase of temperature in the junction, depending on the size of the current pulse and the rate of heat dissipation. Measurements on alloy junction diodes lead to a curve of temperature rise against pulse duration which does not agree with any single theory of heat transfer. Investigating the problem reveals the need to consider a multitude of factors (materials, dimensions, shapes) which cannot be fitted to a single mathematical model. Satisfactory analysis, without undue complications, can be achieved in four successive steps, described in Table I. Considering each step, we assume that the preceding step is transferring heat at a steady rate (i.e., neglecting heat storage) and the following step is not yet subjected to a significant heat flow. Careful selection of boundaries and time limits leads to a valid approximation; or, inversely, an observed pulse-time characteristic can be interpreted by the theory to gain an insight into the modes of internal heat transfer.