CURRENT-VOLTAGE INSTABILITIES IN SUPERLATTICES

A simple model of a series of circuits comprising a nonlinear resistor and a capacitor in parallel is suggested for a description of I-V-characteristic instabilities and the formation of high-field domains in superlattices. The model is justified if subbands in a superlattice are destroyed by a high field or scattering and the transport is sequential tunneling. In the case of a wide second subband, the superlattice breaks down in two parts. In the first, the transport is sequential tunneling, but in the second part, electrons propagate in the second subband and the model breaks down there. Simple physical arguments show that the I-V characteristics of such a superlattice has to have an S shape, which leads to oscillations and more complicated nonstationary phenomena.