Quasi-bound states and intra-band transition energies in GaAs-(Ga,Al)As variably spaced semiconductor superlattices

A theoretical study of multi-quantum-well semiconductor heterostructures under applied electric fields perpendicular to the layers is performed within the transfer-matrix approach. Calculations are carried out for two different variably spaced superlattices, designed in such a way that the conduction-electron states resonate at a certain value of the electric field. We have calculated the density of states for various values of the applied electric field, and results indicate a richly peaked structure associated to quasi-bound states of electrons, heavy holes and light holes. Results shown for the electric-field dependence of the interband transitions associated to electron-hole recombination indicate the possibility of a coherent resonant tunnelling, at a critical field, which may have applications in the design of more efficient solar-cell devices.