Renormalization of the band gap in highly photoexcited type-II ZnSe/BeTe structures

For the type-II ZnSe/BeTe heterostructures, a large (～0.1 eV) red shift of the edge of interband recombination in the ZnSe layers is observed at high densities of spatially separated photoexcited electrons and holes (～10¹³ cm^?2). The observed magnitude of renormalization of the band gap exceeds the magnitudes predicted by the multiparticle theory for dense type-I electron-hole systems at the same concentrations of two-dimensional charge carriers. Numerical calculations show that macroscopic electric fields induced by separated charges have a profound effect on the energy of direct transitions in type-II structures, resulting in an additional decrease in the energy of the transitions. In wide structures, where the ZnSe layer thickness is ? 15 nm, the renormalization effect is less pronounced. This is attributed to incomplete spatial separation of photoexcited charge carriers in the case of profound band bending and, thus, to the less-pronounced effect of electric fields.