COUPLED DEFECT-LEVEL RECOMBINATION - THEORY AND APPLICATION TO ANOMALOUS DIODE CHARACTERISTICS

We calculated the steady-state recombination rate for two coupled defect levels and implemented the model into a device simulator. This model generalizes the familiar single-level Shockley-Read-Hall (SRH) formula. If the intercenter transition probability vanishes, it reduces to the sum of two individual SRH rates, which are only linked via the band occupancies. The cases, where one of the levels or even both behave like traps in carrier capture, and the case of a rate-limiting intercenter transition are derived from the general expression. The important feature of the model is a possible increased field effect which might lead to large excess currents. The field effect is discussed in terms of tunnel-assisted multiphonon capture or direct tunneling into the levels, respectively. We show by means of numerical simulation that the large ideality factors found for Liquid phase epitaxy grown diodes with weak intrinsic fields can be the result of a rapid direct charge transfer between donors and accepters and the high probability of tunneling into the hydrogenic states. (C) 1995 American Institute of Physics.