Theoretical investigation of direct and phonon-assisted tunneling currents in InAlGaAs-InGaAs bulk and quantum well interband tunnel junctions for multi-junction solar cells

Abstract

Direct and phonon-assisted tunneling currents in InAlGaAs-InGaAs bulk and double quantum well interband tunnel heterojunctions are simulated rigorously using the non-equilibrium Green's function formalism for coherent and dissipative quantum transport in combination with a simple two-band tight-binding model for the electronic structure. A realistic band profile and associated built-in electrostatic field is obtained via self-consistent coupling of the transport formalism to Poisson's equation. The model reproduces experimentally observed features in the current-voltage characteristics of the device, such as the structure appearing in the negative differential resistance regime due to quantization of emitter states. Local maps of density of states and current spectrum reveal the impact of quasi-bound states, electric fields and electron-phonon scattering on the interband tunneling current. In this way, resonances appearing in the current through the double quantum well structure in the negative differential resistance regime can be related to the alignment of subbands in the coupled quantum wells.