Optical investigation of CdTe monomolecular islands in wide ZnTe/(Zn,Mg)Te quantum wells: Evidence of a vertical self-ordering.
Résumé
Continuous, piezomodulated, and time-resolved optical spectroscopies have been carried out on several samples basically consisting of a 38-nm-wide ZnTe quantum well incorporating monomolecular CdTe islands grown by molecular-beam epitaxy on nominal (001) ZnTe surfaces. During the growth of some samples, five regularly spaced monomolecular layers (single or half-monolayers) of CdTe were inserted in the wide ZnTe quantum wells. Our results indicate that, under certain conditions of deposition, (i) the fractional layers constitute CdTe islands separated by ZnTe “voids,” with in-plane size and spacing quite larger than the exciton Bohr diameter; and (ii) when several fractional monolayers are grown, these islands tend to stack on top of each other. The effects of this vertical self-ordering disappear when the conditions of deposition are changed. Moreover, it is shown that the CdTe inserts act as giant isoelectronic recombination centers, yielding intense and sharp photoluminescence lines with very short decay times (a few tens of picoseconds) in the range of λ≈517 nm.