Binding of Biexcitons in GaAs/AlGaAs Superlattices

Abstract

Binding of the heavy-hole excitons and biexcitons in GaAs/Al 0.3 Ga0.7As superlattices is studied using linear and nonlinear optical techniques. High biexciton binding energies characteristic of quasi two-dimensional biexcitons are observed in superlattices with considerable miniband dispersion.PACS numbers: 71.35. Cc, 78.66.Ηf, 42.50.Md Binding energies of Coulomb-bound states, namely the heavy-hole (HΗ) excitons and biexcitons in GaAs/AlGaAs multiple quantum wells (MQW) and superlattices (SL) are significantly enhanced compared to bulk GaAs. The main reason for this enhancement is the one-dimensional confinement of the electrons and holes along the direction of growth. By now it is established that in the limiting three-dimensional (3D) and twodimensional (2D) cases, the ratio of the biexciton to the exciton binding energy σ = Εxxb/Ε is a constant. In 3D it is given by the Haynes rule [11:It is interesting to investigate this ratio for intermediately confined systems which are neither strictly 2D nor 3D. Obviously, a transformation from (2) to (1) must accompany the 2D-3D transition. In MQW systems, where the confinement is mostly determined by the geometric GaAs well thickness Lw , a constant value of σ 0.2 in agreement to (2) was found, while L w was varied within the 80-160 Α range [3].In this work we present a similar study of GaAs/AlGaAs samples having the same well width, but different AlGaAs barrier widths Lb. Thus, we investigate the transition from a MQW to SL structure, and associated change of dimensionality. The samples investigated are MBE-grown on (100) semi-insulating GaAs substrates, and consist of 20 GaAs/Al 0.3Ga 0.7As periods. In all samples (923)