Core/Shell HgCdTe/HgCdSe Quantum Dots for Wave Function Engineering with Infrared Band Gaps

Abstract

Semiconductor quantum dots (QDs) are a class of nanomaterials with tunable electronic structure that enables precise control of light–matter interactions for diverse optoelectronic applications. Mercury cadmium chalcogenides are an emerging QD composition for infrared photonic applications, and their heterostructures are expected to expand functionality. Here, we introduce core/shell HgCdTe/HgCdSe QDs with bandgap energies in the infrared and charge carrier wave functions controlled by domain dimensions and the radial distribution of mercury and cadmium. As prepared via mercury cation exchange of core/shell CdTe/CdSe QDs, mercury can be selectively concentrated in either the core or shell, and can fully deplete cadmium to generate HgTe/HgSe QDs. Different alloying regimes shift band offsets between type-I and type-II alignments, in which the electron and hole are colocalized or separated, respectively. Broad bandgap tunability across the infrared spectra with long-term stability in air addresses problems of the constituent QD homostructures of HgTe and HgCdTe with low chemical stability and HgSe and HgCdSe with n-type doping. The photophysical features and oscillator strengths are reported as figures of merit and compared with quantum mechanical calculations. An optical metrology method based on ultraviolet E1 critical-point features is also introduced for assaying cation distributions, which is otherwise difficult in small core/shell QDs. These small-bandgap QDs with controllable charge carrier wave functions offer new opportunities to investigate photoluminescence, excited-state photophysics, and light–matter interactions at infrared wavelengths.