Effect of Surface Chemistry on the Continuum Intensity in CdTe Quantum Dots

Abstract We investigate the surface chemistry dependence of the absorption spectra in 3.2 nm CdTe quantum dots (QDs) using room-temperature absorption spectroscopy. More specifically, we focus on the broad bulk-like contribution commonly referred to as the continuum. Modification of the surface stoichiometry from Cd-rich to Te-rich conditions results in a pronounced increase in the continuum absorption intensity, particularly in the region between the 1Se–1Sh and 1Se–2Sh transitions. In contrast, the absorption at higher energies is comparatively insensitive to surface stoichiometry. We assign the continuum absorption to two distinct types of transitions: (i) low-energy transitions that involve transferring an electron from a surface chalcogenide dangling-bond to a quantum-confined conduction-band state and (ii) high-energy bulk-like transitions that scale with particle volume. We also find that the same considerations apply to continuum transitions involving adsorbed alkylthiols. We further apply this model to interpret the spectroscopic data of metal- and chalcogenide-rich ZnSe and CdSe quantum dots reported in the literature. This analysis provides a consistent interpretation of continuum absorption in semiconductor quantum dots and highlights the role of surface stoichiometry in determining optical spectra.