Lifetime profile measurements in heavily doped emitter structures using electron beams

An electron beam technique for depth profiling of minority carrier lifetime in heavily doped emitter structures is described. The method is based on generation of electron hole pairs at varying depths by an electron beam of variable energy. Modeling of the current flow equaitons is used to predict the dependance of collected current at the junction as a function of electron beam energy. Comparison of these model calculations to the experimental data shows that for the device studied the lifetime near the heavily doped surface is 10^-8sec increasing as - 0.4 power of the net doping. This technique is complementary to emitter gain measurements which are most sensitive to lifetime near the junction.