Quantum confinement effects at theLpoint 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+Δ₁ 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 k{·}p 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.