Transport of minority- carriers in graded-composition semiconductors and its impact on graded-band-gap base transistors operated at high currents

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Abstract
A comprehensive model for minority‐carrier transport due to a quasi‐electric‐field in graded‐composition semiconductor materials is developed including effects due to nondegenerate high‐level injection of excess electrons and holes. For low‐level injection, equivalent to a one‐sun photoexcitation of uniformly doped direct‐ or indirect‐band‐gap material the total quasifield is given by the standard gradient of band‐gap energy. High‐level injection asymptotically reduces quasifield components due to band‐gap and effective‐mass gradients to lower values, and essentially eliminates components due to equilibrium‐ and excess‐carrier concentration gradients. The impact of these results on performance of p‐n‐p and n‐p‐n graded‐band‐gap base transistors operated at high currents is examined.