Quantum confinement effects at the L point in CdTe

We report quantum-size-related shifts in optical transitions originating away from the center of the Brillouin zone of a II-VI semiconductor. CdTe-glass composite thin films, containing isolated semiconductor crystallites with average sizes ranging from 46 to 158, exhibit a size-dependent blue shift of the E1 and E1+1 transitions occurring at the L point of the zinc-blende Brillouin zone. Analysis of the effect, in the context of current zone-center confinement theory, supports the existence of bound electron-hole pairs whose internal motion is restricted to two dimensions. The effective mass governing the energy shift of each transition falls within at least 5% of the corresponding total transverse mass of the electron and hole calculated using kp theory for the bulk material. It thus appears that, within the crystal size regime of the present study, optical absorption into these energy states results in the formation of a fully correlated two-particle state whose behavior is analogous to that of a single quasiparticle confined within the crystallite.