Transient temperature behavior in pulsed double-drift IMPATT diodes

The temperatures in a pulsed double-drift IMPATT diode are calculated as a function of position and time by a finite difference calculation using the alternating direction algorithm. The results are given as a function of pulse length and duty factor for a typical double-drift diode designed to operate near X band. Techniques are described for choosing spatial meshes and time integrals which vary with position and time in a way that minimizes computation time. Numerical results are chosen to illustrate the distribution of temperature within the diode at different times during the pulse, the effect of a temperature-dependent breakdown voltage upon radial temperature distribution, and the interplay between the short thermal-diffusion times within the GaAs diode and the long times associated with the slow heating-up of the heat sink at great distances. An extended definition of thermal resistance for pulsed diodes is introduced and the implications upon reliability are discussed.