SELF-HEATING EFFECTS IN BASIC SEMICONDUCTOR STRUCTURES

We have investigated the effects of self-heating on the high current I -V characteristics of semiconductor structures using a fully coupled e lectrothermal device simulator. The underlying physical mechanisms are highlighted from analyses of simulation results for basic resistors a nd reverse-biased diodes. It is shown that the breakdown in both resis tors and diodes is caused by conductivity modulation due to minority c arrier generation. In isothermal simulations with T = 300 K, avalanche generation is the source of minority carriers. In simulations with se lf-heating, both avalanche and thermal generation of minority carriers can contribute to the breakdown mechanism. The voltage and current at breakdown are dependent on the structure of the device and the doping concentration in the region with lower doping. For all structures, ex cept highly doped resistors with poor heat sinking at the contacts, th e temperature at thermal breakdown ranged from 1.25T(i) to 3T(i), wher e T(i) is the temperature at which the semiconductor goes intrinsic. H ence, it is found that T = T(i) is not a general condition for thermal (or second) breakdown. From these studies, an improved condition for thermal breakdown is proposed, based on the rate of minority carrier g eneration as a function of temperature increase and the rate at which temperature increases with power dissipation in the device. We have nu merically verified this condition for the devices studied here.