OPTICAL INVESTIGATION OF CDTE MONOMOLECULAR ISLANDS IN WIDE ZNTE (ZN,MG)TE QUANTUM-WELLS - EVIDENCE OF A VERTICAL SELF-ORDERING/

Continuous, piezomodulated, and time-resolved optical spectroscopies h ave been carried out on several samples basically consisting of a 38-n m-wide ZnTe quantum well incorporating monomolecular CdTe islands grow n by molecular-beam epitaxy on nominal (001) ZnTe surfaces. During the growth of some samples: five regularly spaced monomolecular layers (s ingle or half-monolayers) of CdTe were inserted in the wide ZnTe quant um wells. Our results indicate that, under certain conditions of depos ition, (i) the fractional layers constitute CdTe islands separated by ZnTe ''voids,'' with in-plane size and spacing quite larger than the e xciton Bohr diameter; and (ii) when several fractional monolayers are grown, these islands tend to stack on top of each other. The effects o f this vertical self-ordering disappear when the conditions of deposit ion are changed. Moreover, it is shown that the CdTe inserts act as gi ant isoelectronic recombination centers, yielding intense and sharp ph otoluminescence lines with very short decay times (a few tens; of pico seconds) in the range of lambda approximate to 517 nm.