Resonant Energy Transfer Based Electrically Pumped Hybrid Lasers

Realization of electrically pumped compact and reliable lasers with low-threshold current densities and tunable emission wavelengths made from inexpensive, solution processable materials will have a revolutionary impact on many disciplines including photonics, chemical sensing, and medical diagnostics. Colloidal semiconductor quantum dots (CQDs) are attractive nanomaterials for achieving this goal because they can be fabricated using easily scalable chemical techniques, and their optical properties can be directly controlled via the quantum confinement effect. Compared to other approaches, CQDs offer practically unmatched flexibility of highly controllable structural properties by using surface modifications and formation of CD heterostructures. However, low carrier mobilities and poor thermal conductivity of CQD thin films are currently the major challenges for their applications in electrically pumped lasers. The proposed project specifically addresses these challenges and offers promising solution for the development of novel coherent light sources based on resonant energy transfer (RET) in hybrid nanostructures comprised of epitaxial Si/SiGe nanolayers and Pb-based CQD thin films. Advances from this research project will be disseminated widely through publications, conference presentations, academic courses, undergraduate and graduate student research experience and summer programs for local high school students. RET is a short-range non-radiative resonant energy transfer process from an energy donor to acceptor via dipole-dipole interaction. Normally, RET co-exists with the undesirable energy back transfer (EBT), but the proposed in this project device design and choice of nanomaterials should suppress EBT. In addition, charge carrier mobility and thermal conductivity in epitaxial Si/SiGe nanostructures are orders of magnitudes better compared to that in CQD thin films, and the level of carrier injection is expected to be sufficient to achieve population inversion. Also, the proposed approach is specifically focused on hybrid nanostructures designed to make the RET rate orders of magnitudes greater compared to competing processes of energy relaxation, such as Auger and defect related carrier recombination. To achieve this goal, novel Pb-based core-shell CQDs with highly controllable interface composition will be developed using advances in synthetic chemistry and allowing epitaxial coverage of a QD core by a shell with a thickness of an atomic monolayer. In these composition-controlled core-shell CQDs Auger recombination is expected to be suppressed and favorable conditions for optical amplification can be achieved. In addition, the proposed research addresses other key issues for electrically pumped CQD lasers including design of carrier injectors, control over exiton locations and formation of low-defect density interfaces. The anticipated results will contribute to realization of electrically pumped CQD-based lasers with QDs of different compositions and provide a promising route for the development of novel coherent light sources for multiple applications.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.