Bandgap tuning in ZnSe quantum dots through heterovalent indium alloying

초록

Heavy-metal-free colloidal quantum dots (QDs) with broad spectral coverage are required for ecofriendly optoelectronics. While conventional bandgap tuning relies on a size-dependent quantum confinement effect, compositional engineering through heterovalent substitution offers a better alternative to tailor the electronic band structure. In this study, we synthesize heavy metal-free Zn(In)Se alloy QDs using a single-step heat-up method. The intrinsic wide bandgap can be narrowed successfully via the heterovalent incorporation of In3 + into a cubic zinc blende ZnSe lattice without secondary phase segregation. This alloying approach induces a pronounced red shift in the absorption edge, tuning the optical bandgap from blue to orange based on the Zn:In ratio. Ultraviolet photoelectron spectroscopy combined with optical bandgap analysis reveals that, upon indium incorporation, the valence band maximum and conduction band minimum shift upward relative to the vacuum level. This is accompanied by an upward shift of the Fermi level because of the donor-like behavior of In3+ substitution in the ZnSe lattice. As a proof-of-concept, Zn(In)Se QDs are incorporated into a hybrid photodetector with an organic semiconductor Y6. Given their strong absorption in the 400-500 nm region, Zn(In)Se QDs complement the long-wavelength absorption of Y6, which enables broadband photodetection spanning the entire visible to near-infrared spectral range. These results confirm that heterovalent indium alloying provides an effective strategy to engineer the electronic structure and optical properties of ZnSe-based QDs and highlight their potential for optoelectronic applications.

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