Avalanche breakdown mechanism originating from Gamma-X-Gamma transfer in GaAs/AlAs superlattices

An avalanche breakdown mechanism in GaAs/AlAs type-I superlattices is demonstrated. This mechanism shows its power at a bias voltage where both of the following two conditions are met. One is electron transfer from the Gamma ground state to the X ground state (Gamma(1)-X-1), and the other is the escape of electrons from the X-1 state to the second Gamma state (X-1-Gamma(2)). Under both conditions, because the AlAs barriers become transparent for electron transport due to the Gamma(1)-X-1-Gamma(2) path, the drift speed (i.e., the acceleration of electrons) grows, and then the superlattice shows the phenomenon of avalanche breakdown. From our experimental results for various GaAs/AlAs superlattices, it is thought that such avalanche breakdown frequently occurs when type-I GaAs/AlAs superlattices have thick barrier widths. (C) 1997 American Institute of Physics. [S0003-6951(97)04245-9].