A Formation Mechanism of X Level due to an Indium-Carbon Dimer in Silicon

Abstract

It is known that acceptor-carbon complexes have ionization energies less than those of the corresponding substitutional, separate acceptors in silicon. We present the formation mechanism for a shallower acceptor energy level called an X level that is due to an indium- carbon pair. Ab initio calculation methods were used to evaluate electronic structures and lattice relaxations of silicon with indium, carbon or a carbon-indium dimer. The results shows that the bonding interaction between the 5p orbitals of the indium atom and the 3sp orbitals of the silicon atoms bound with the indium atom mainly determines the ionization energy of the X level, and the ionic bonding interaction of the carbon atomic orbitals with the indium atomic orbitals in the X level enables the bonding interaction of the orbitals between the indium atom and the silicon atom to lower the corresponding indium acceptor level, and then to form the shallower X level.

Formation Energy Calculations of Impurity Elements at Substitutional or Interstitial Sites in Silicon

“…However, it is difficult to form such source/drain junctions, because of the lack of dopants with extremely low diffusivity and high solubility. Some of potential replacements for the conventional dopants have been proposed to be cluster dopants [1,2], dimer co-dopants [3] and trimer co-dopants [4,5]. These proposals showed that the cluster dopants and the co-dopants had the marked effects on the reduction of ionization energies and the increase of carrier concentrations, compared with that of the corresponding single dopant.…”