Atomistic tight-binding theory for acceptor states (C, Be, Mg, Zn, Si and Cd) of GaAs nanocrystals

Abstract

The atomistic tight-binding theory is introduced as a new way to numerically calculate the binding energies of acceptors (C, Be, Mg, Zn, Si and Cd) in GaAs nanocrystals. In the present paper, the electronic structures and optical properties of spherical GaAs nanocrystals with a single substitutional acceptor impurity at the center and off-center sites are studied. The optical band gaps of undoped GaAs nanocrystals are larger for smaller nanocrystals, due to quantum confinement effects. Numerical results show that the acceptor binding energies are highly dependent on the nanoparticle sizes, impurity types and positions. Larger acceptor binding energies in doped GaAs nanocrystals are also seen for smaller nanocrystals. In term of acceptor varieties, the high-to-low order of binding energies is found in Cd, Si, Zn, Mg, Be and C acceptors, respectively. In term of positions, the acceptor binding energies are reduced with the increasing distances from the center of nanocrystals. In addition, the optical property is mainly improved in the presence of the substitutional acceptor impurity. Finally, these computational results provide an inroad to new materials not accessible via other means with the aim to implement novel applications based on the substitutional acceptor impurity in the nanostructures.