We have simulated multiexciton generation (MEG) processes in Si and Ge nanocrystals, employing the equation of motion coupled cluster single and double as a high-level ab initio approach. Simulations, consistent with the experimental results reported so far, reveal the key role of the d-polarized valence component in the chosen basis set on the accuracy and reliability of the results. Moreover, the MEG thresholds calculated with def2SVP basis set are ∼8.23(8.07) eV for seven (eight)-atom Si clusters and ∼7.58(6.84) eV for similar Ge clusters. The normalized MEG thresholds of Ge nanocrystals are 8% smaller with respect to Si. Thus, in contrast to Si, they are more appealing to the optical device designers for enhancing the device quantum efficiency. Furthermore, the resemblance of the symmetry of the simulated seven-atom clusters to those of the experimentally domelike grown nanocrystals makes the behavior of their MEG quantum probability similar.
Gordi, Mahdi, Hamidreza Ramezani, and Mohammad Kazem Moravvej-Farshi. 2017. “Multiple Exciton Generation in Si and Ge Nanocrystals: An Ab Initio Comparative Study.” The Journal of Physical Chemistry C 121 (11): 6374–79. https://doi.org/10.1021/acs.jpcc.7b00512.