QUANTITATIVE MODELING OF DC AND TRANSIENT CHARACTERISTICS AT HIGH INJECTION LEVEL AT 77 AND 300 K IN SILICON BIPOLAR-TRANSISTOR

The current gain of a silicon bipolar transistor has been quantitative ly modelled by the Early effect, the conductivity modulation effects i n the base and in emitter, the effective base widening effect and the emitter current crowding effect at 77 and 300 K involved in the carrie r recombination currents in the emitter-base space charge region and i n the base. On this basis, the transit times, the total transit time f rom the emitter to collector and the cutoff frequency are modelled as functions of the collector current at 77 and 300 K. The results obtain ed are in agreement with the experimental data. Besides this, the infl uence of the maximum base doping concentration on the maximum current gain and the maximum cutoff frequency has been also analysed. The main results show that the current gain is mainly determined by the conduc tivity modulation effect and the emitter current crowding effect at hi gh injection level at 77 K, but at 300 K it is mainly determined by th e effective base widening effect. The cutoff frequency is mainly deter mined by the minority-carrier base transit time at 300 K, and at 77 K the minority-carrier emitter transit time may be dominant for the larg e bandgap narrowing effect in emitter. The bandgap narrowing effect is the main reason for the degradation of the cutoff frequency with lowe ring temperature, instead of the low-temperature trapping effect by th e compensated impurities with the shallow energy levels.