Computational modeling of quantum-confined impact ionization in Si nanocrystals embedded in SiO2

Injected carriers from the contacts to delocalized bulk states of the oxide matrix via Fowler–Nordheim tunneling can give rise to quantum-confined impact ionization (QCII) of the nanocrystal (NC) valence electrons. This process is responsible for the creation of confined excitons in NCs, which is a key luminescence mechanism. For a realistic modeling of QCII in Si NCs, a number of tools are combined: ensemble Monte Carlo (EMC) charge transport, ab initio modeling for oxide matrix, pseudopotential NC electronic states together with the closed-form analytical expression for the Coulomb matrix element of the QCII. To characterize the transport properties of the embedding amorphous SiO₂, ab initio band structure and density of states of the α-quartz phase of SiO₂ are employed. The confined states of the Si NC are obtained by solving the atomistic pseudopotential Hamiltonian. With these ingredients, realistic modeling of the QCII process involving a SiO₂ bulk state hot carrier and the NC valence electrons is provided.