Dopant Effects on Single and Multiple Excitons in Small Si Clusters: High-Level Ab Initio Calculations

Doping has been critical to the realization of current semiconductor devices, allowing for control and tuning of the electronic properties. Whereas doping is now common in bulk, its extension to spatially confined materials has not been easy. Recently, suitable synthetic methods have been developed, and it has become vital to understand the changes doping affects in spatially confined materials. For this purpose, we performed high-level, ab initio quantum-chemical calculations on small boron- and phosphorus-doped Si clusters, and obtained optical absorption spectra and excited states properties over a broad energy range, including single and multiple excitons. We find that doping blue-shifts the optical absorption spectra and moves the onset of multiexciton configurations to significantly higher energies. The latter factor can be very important in photovoltaic applications. The effect of doping on the cluster properties is similar to that of charging.