Science and technology at nanoscale have numerous opportunities both for fundamental research and new applications. Quantum dots, nanocrystals, nanowires, and nanorods are among the most important building blocks of nano-photonic devices. Therefore, the understanding of underlying fundamental physical phenomena in such structures is very important for future progress. We are interested in fundamental properties of wide bad gap nanostructured materials, particularly those with type-II band alignment, with potential application in photo-detection, quantum information, and biomedical field. Type-II heterostructures have several substantial advantages over type-I systems in that that they suppress non-radiative Auger recombination, and their emission can be controlled by external means such as intensity of excitation, electric and magnetic fields. We particularly focused on properties of epitaxial ZnTe/ZnSe quantum dot multilayers
and related alloys, type-II colloidal core-shell nanoparticles, and II-VI nanowires.
In the ZnTe-ZnSe systems holes are strongly confined within ZnTe-rich quantum dots, whereas electrons locate in ZnSe barriers, and only weakly attracted to holes via the Coulomb interaction, forming the spatially indirect (type-II) excitons. It is important that QDs in this system coexist with Ten
isoelectronic centers, and a smooth transition between these two different species is indicated by experimental results. Therefore, QDs here are formed by continuing enlargement of Ten
/Se isoelectronic centers. In magnetic field this system exhibits one of the most interesting quantum phenomena - so-called optical Aharonov-Bohm Effect
, for which we observed photoluminescence intensity as well as energy oscillations within the same sample
, experimentally, for the first time. The samples are grown by Prof. M. C. Tamargo’s
group of The City College. Other similar systems, for instance ZnTe/ZnCdSe multilayers of submonolayer type-II QDs, can be used as intermediate band material
in QD-based intermediate-band solar cells; such solar cells can have efficiency as high as 63% under full solar concentration. We are interested in both material properties and application of this material system.
In addition to epitaxial quantum dots we, currently, are working on several aspects of optical properties of colloidal ZnO nanostructures, including core-shell systems. We have shown that quantum size effects can be achieved in ZnO nanorods
, and we continue to investigate the role of dielectric confinement on ZnO nanorods optical properties, as it is important for 1-D systems. We investigate also the role of morphology
on the optical properties of ZnO nanostrutures, including origin of the green band
. Recently, we began growing ZnO nanowires using in-house built CVD system.
We are also working in application of type-II structures for high sensitivity biological detectors. This work is in collaboration with Prof. Mourokh and Prof. H. Matsui
of Hunter College. The pathogen diagnostics is constrained by a variety of challeneges that compromise essential elements of detection. Our approach
uses unique optical properties of type-II colloidal fluorescent quantum dots.