Multiband treatment of quantum transport in interband tunnel devices

We describe a method for computing transmission coefficients for multiband tight-binding band-structure models. In this method, the transmission probability can be calculated simply by solving a system of linear equations representing the tight-binding form of the Schro¨dinger equation over a finite region of interest, with specially formulated boundary and inhomogeneous terms to account for the effects of the incoming and outgoing plane-wave states. In addition to being efficient, and simple to implement, our method is numerically stable in treating device structures with large active regions, and therefore capable of modeling realistic band-bending effects. Using this method, we examine transport properties in InAs/GaSb/AlSb-based interband tunnel structures with a realistic band-structure model. We compare our results with calculations obtained with a two-band model, which includes only the lowest conduction band and the light-hole band. We find that while the primary interband transport mechanism arises from the coupling between the InAs conduction-band states and GaSb light-hole states, in device structures containing GaSb quantum wells, the inclusion of heavy-hole states can introduce additional transmission resonances and substantial hole-mixing effects. These effects are found to have a significant influence on the current-voltage characteristics of interband devices.