CHOOSING PROPER APPROXIMATION FOR SEMICONDUCTOR-DEVICE ANALYTICAL MODELING AT LOW-TEMPERATURE

The influence of nonlinear physical phenomena (namely electron-hole sc attering, Auger recombination, reduction of the emitter junction effic iency) on the practicality of diffusive approximation in semiconductor multilayer device modeling is investigated. It is shown that there ex ists a certain sequence of proper ap proximations as the current densi ty increases. An important point is that this sequence of approximatio ns depends on the electrophysical parameters of the structure, namely on the ratio W/L (where W is the width of a lightly doped base layer o f the structure, L is the ambipolar diffusion length of charge carrier s in the base layer), the charge carrier lifetime tau and the saturati on currents j(sn) and j(sp) of highly doped p(+) and n(+) layers. It i s shown that at low temperature the dependence of saturation currents on electron-hole scattering becomes of importance. Owing to this the e lectron-hole scattering influences the validity of diffusive approxima tion as distinct from the case of high temperature