Speakers
Description
Density functional theory modelling was used to gain more insights on the interaction of germanium (Ge), tin (Sn) and lead (Pb) dopants with a vacancy. These interactions are often used to control vacancies in silicon in order to avoid the formation of unwanted vacancy complexes. We studied the structure, formation energies, binding energies and the charge state transition energy levels of these defect complexes.
In our research we used Quantum Espresso with the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional to model the defect in a 64-atom supercell. We compare our results with the results of previous calculations using the VASP package using similar parameters.
Quantum confinement effects and finite size corrections were investigated using larger supercells including 216, 512, and 1000 atoms. The results were found to be closer to the previously computed defect level as the supercell size increased. For larger supercells, the band gap predicted by the HSE functional together with the formation energy obtained using the generalised gradient approximation (GGA) was used to plot graphs of formation energy as a function of the Fermi-level in order to determine the charge state transition energy levels. We found that, using the HSE band gaps and by increasing the supercell size, we could use the results of the formation energies calculated using the GGA to accurately predict the defect levels of the defect complexes. We found that Quantum Espresso and VASP gave similar results. We also found that using the GGA functional together with the HSE band gap can accurately predict the defect levels of defect complexes with major saving in computational costs.
