Investigation of inverse photoemission and field-assisted radiative electron capture in semiconductor nanoparticles

This work presents a theoretical and computational investigation of the electron affinities, electron-capture cross-sections, inverse photoemission energies, and inverse photoemission cross-sections for a series of PbS, PbSe, CdS, and CdSe quantum dots. Inverse photoemission occurs when an incident electron is captured by a material in one of the high energy unoccupied states which then subsequently de-excites to the lowest unoccupied molecular orbital (LUMO) state by emitting a photon. Using the kinetic energy of the captured electron and the energy of the generated photon, one can back-calculate the information about the unoccupied states. Inverse photoemission allows for direct spectroscopic investigation of the conduction band and is used in surface characterization of solids. This theoretical and computational study uses diagrammatic time-dependent many-body perturbation theory and 1-particle Green's function method to calculate the electron capture cross-section, photon emission oscillator strength, and the overall inverse photoemission cross-section in quantum dots. The results from this study show that the quantities related to the electron capture process and the photoemission process follow different size-dependent scaling laws with respect to increasing dot size. To enhance the inverse photoemission process, we demonstrate that the overall radiative electron capture cross section of quantum dots can be significantly increased by application of external electric field.