Off-zone-center or indirect band-gap-like hole transport in heterostructures

Unintuitive hole transport phenomena through heterostructures are presented. It is shown that for large bias ranges the majority of carriers travel outside the Gamma zone center (i.e., more carriers travel through the structure at an angle than straight through). Strong interaction of heavy-, light-, and split-off hole bands due to heterostructure interfaces present in devices such as resonant tunneling diodes, quantum-well photodetectors, and lasers are shown to be the cause. The result is obtained by careful numerical analysis of the hole transport as a function of the transverse momentum k in a resonant tunneling diode within the framework of a sp3s* second-nearest-neighbor tight-binding model. Three independent mechanisms that generate off-zone-center current flow are explained: (1) nonmonotonic (electronlike) hole dispersion, (2) lighter quantum well than emitter effective masses, and (3) strongly momentum-dependent quantum-well coupling strength due to state anticrossings. Finally a simulation is compared to experimental data to exemplify the importance of a full numerical transverse momentum integration versus a Tsu-Esaki approximation.