Time-resolved luminescence spectroscopy of recombination dynamics in a ZnSSe doping superlattice

Abstract

The recombination dynamics in a ZnSSe doping superlattice has been studied by means of time-resolved photoluminescence (PL) spectroscopy. The layer consisted of a GaAs buffer (260 nm), a ZnSe buffer (20 nm), an undoped ZnS0.064 Se0.936 buffer (300 nm) and ten periods of doping superlattice. The p- and n-doped layers were each 200 Å in thickness and were equally doped to an impurity concentration of 7 × 1017cm−3. The PL peak energies at 77 K ranged from 2.736 to 2.578 eV as the incident laser power was reduced by orders of magnitude of about 5.7. The peak energy shift of 158 meV fairly agrees with the calculated space charge potential under equilibrium conditions. It has been found that the recombination process under low excitation is a tunneling transition between electrons and holes spatially separated by the built-in potential, and it changes to a nearly vertical transition under the highest excitation as a result of the formation of a flat band induced by excess photo-generated carriers.