EXCITONIC OPTICAL-TRANSITIONS AS A PROBE OF SELF-ORGANIZED GROWTH OF ZNTE (CDTE) ISLANDS IN (001)-GROWN CDTE (ZNTE) QUANTUM-WELLS

integer or half monolayers of CdTe have been deposited, every 20 monol ayers, in 120-monolayer wide ZnTe/(Zn,Mg)Te quantum wells, by molecula r beam epitaxy or atomic layer epitaxy on nominal (001) surfaces of Zn Te substrates. Low-temperature direct and piezomodulated reflectivity as well as C.W. and time-resolved photoluminescence have been taken fr om these samples. By comparison of samples grown in slightly different ways, we conclude that fractional CdTe layers, separated by a few ZnT e monolayers, grown in a Zn-rich environment, tend to grow in an order ed way: successive CdTe islands are stacked in vertical columns separa ted by columnar 'voids' of pure ZnTe. This behavior is the opposite of the staggered lineup of ZnTe islands in CdTe-(Cd,Zn)Te quantum wells, grown on Cd-rich substrates, recently observed by similar experimenta l techniques. Both behaviors are tentatively explained in terms of the relative stiffnesses of the materials of the inserts and of the matri x. (C) 1998 Academic Press.