Enhanced Multiple Exciton Generation in Amorphous Silicon Nanoparticles

Multiple exciton generation (MEG) in nanometer-sized hydrogen-passivated silicon nanowires (NWs), and quasi two-dimensional nanofilms strongly depends on the degree of the core structural disorder as shown by the many-body perturbation theory (MBPT) calculations based on the density functional theory (DFT) simulations. Working to the second order in the electron-photon coupling and in the screened Coulomb interaction we calculate quantum efficiency (QE), the average number of excitons created by a single absorbed photon, in the ${\rm Si}_{29}{\rm H}_{36}$ quantum dots (QDs) with crystalline and amorphous core structures, simple cubic three-dimensional arrays constructed from these QDs, crystalline and amorphous NWs, and quasi two-dimensional silicon nanofilms, also both crystalline and amorphous. Efficient MEG with QE of 1.3 up to 1.8 at the photon energy of about $3E_g$, where $E_g$ is the electronic gap, is predicted in these nanoparticles except for the crystalline NW and crystalline film where $QE\simeq 1.$ MEG in the amorphous nanoparticles is enhanced by the electron localization due to structural disorder. Combined with the lower gaps, the nanometer-sized amorphous silicon NWs and films are predicted to have effective carrier multiplication within the solar spectrum range.