Avalanche breakdown mechanism originating from Γ–X–Γ 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 $Γ$ ground state to the X ground state $(Γ1$$-X1)$⁠, and the other is the escape of electrons from the X₁ state to the second $Γ$ state $(X1-Γ2)$⁠. Under both conditions, because the AlAs barriers become transparent for electron transport due to the $Γ1$$-X1$$-Γ2$ 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.