Type-II biexcitons in GaAs/AlAs short-period superlattices

We report on the photoluminescence properties of type-II biexcitons consisting of the X electrons of AlAs and Gamma heavy holes of GaAs in (GaAs)(m)/(AlAs)(n) short-period superlattices with (m, n) = (13, 13), (12, 12), (10, 10), (10, 14), and (10, 20) in units of monolayer. In all the samples, we have observed the biexciton formation with a superlinear dependence of the excitation power. From the line-shape analysis of the photoluminescence bands, the biexciton binding energies are estimated to be around 3 meV. We find that the biexciton binding energy decreases with the increase of the AlAs layer thickness in the (10, it) superlattices. This indicates that the spatial separation of electrons and holes of the type-II biexciton affects the binding energy. In addition, we discuss the transient processes of the type-II biexciton from time-resolved photoluminescence spectra. (C) 1998 Elsevier Science B.V. All rights reserved.