Publication date: 15th December 2025
InP and InAs QDs are considered the most promising RoHS complient quantum dot materials for visible and short-wave infrared (SWIR) applications. However, compared to more traditional II-VI QDs they pose additional challenges: (1) InP and InAs are considerably more oxylophilic, so that their surfaces and core-shell interfaces are nearly always oxidized, (2) the high valence of the ions requires high surface coverage with typical 1- X-type ligands to maintain charge balence and (3) the best shell material is ZnSe, where the III-V/II-VI core shell interface is inherently charged, and the properties of teh core-shell QDs depend on subte atomistic details at the interface.
I will discuss recent experiments of our group on the fluorination and oxidation of InP, InAs and InP/ZnSe QDs. As synthesized InP have very low photoluminescence quantum yields (PLQYs), but these can be enhanced to near unity for InP and to ~20% for InAs QDs using mild etching via in situ HF generation[1] or direct addition of InF3.[2] In both cases this results in the formation of InF3 terminated surfaces and a drastic increase in PLQY. I will show that the same methods work on InAs QDs, and that this can be used to fabricate SWIR photodiodes with lower dark current and enhanced EQE.
Perhaps surprisingly, the above fluorination methods do not reduce the amount of oxygen on the surface. Using solid state NMR it can be shown that a significant amount of PO4 is present at the interface of InP/ZnSe QDs, even for high PLQY samples. Isotope labeled 77Se experiments demonstrate that the presence of abundant oxygen at the interface disrupts epitaxial shell growth.[3] In our experiments this is accompanied by a lower PLQY of the resulting samples, although other reports show that interfacial oxidation can be beneficial.[4]
Clearly the III-V/II-VI interface is complex understanding the atomistic composition and its effect on the QD properties remains an open challenge.
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