Optical properties versus growth conditions of CdTe submonolayers inserted in ZnTe quantum wells.
Résumé
Standard and piezomodulated optical spectroscopy is performed on ZnTe quantum wells embedding integer and fractional monolayers of CdTe. The samples, grown in a molecular-beam-epitaxy setup on the (001) surface of ZnTe substrates, all basically consist of 120-ML-wide ZnTe/(Zn,Mg)Te quantum wells, and some of them contain five equally spaced full or half-monolayers of CdTe, producing monomolecular islands of CdTe “buried” in the wide host ZnTe well. The latter behave as efficient recombination centers for excitons. In order to change the size and the configuration of the islands, various growth parameters have been changed between the different samples, e.g., the growth process (molecular-beam epitaxy of binaries or ternaries, or atomic-layer epitaxy) or the temperature. From spectroscopic measurements, the influence of these parameters is analyzed in detail, in terms of the size of the islands and of their in-plane spacing, or of the vertical correlation between these islands. The internal strain state of the CdTe insertions and the overall photoluminescence efficiency are also studied versus growth conditions.