Effective carrier lifetime and base-widening in shortp ⁺ nn ⁺-diodes

Abstract

The paper shows the charge storage behavior of short psn-silicon diodes under the condition of quasi-stationary equilibrium. Recombination in such diodes in the region of high current injection is characterized by an effective lifetime τ _F which may be determined simply by measuring the chargeQ _s stored in the forward biased diode. For short base widthsw<L _B the recombination in the weaklyn-doped middle region is negligibly small in relation to that in the high-doped contacts. The effective lifetime of the charge carriers injected into the middle region is, except for an additive quantity, identical with the mean transit timeT

$$\tau _F = T + T_0 .$$

The injected charge carriers travel without recombination during a transit timeT through the base widthw, given by the doping profile, and then recombine in the high-doped contacts. A parameterw ₀ interpreted as ‘base-widening’ leads in a simplified concept to an effective storage regionw _eff =w+w ₀. The parameterw ₀ can be associated in the experiment with an additional storage effect in then ⁺-substrate. The storage effects in all three layers of the psn-structure are discussed theoretically.