The binding energies of an off-center hydrogenic donor impurity in a GaAs/GaAlAs nanowire superlattice: Comparison between spherical and cylindrical wells

Abstract

In this paper, the effect of an off-center donor impurity on electronic structure of nanowire superlattices (NWSLs) is numerically studied using finite difference (FD) approximation. Energy levels and binding energies of ground and first excited states (1s and 2p) are computed for two different NWSL with circular cross-section which involved an array of spherical or cylindrical quantum dots (QDs) along their axis which are called Sph and Cyl NWSLs, respectively. The numerical results show that oscillatory behaviors appear in electronic energy levels and binding energies as impurity shifts away from the center of QDs. Maximum values of ground state binding energies occur when impurity is located at the center of QDs and these values shift towards higher energies as number of unit cells of NWSL decreases. An opposite behavior is observed for first excited state as impurity shifts away from the center of QDs. Also, as the QDs' volumes increase binding energies (i) decrease, (ii) increase, (iii) decrease, reach minimum values and then increase, or (iv) increase, reach maximum values and then decrease; which strongly depend on the type of NWSL, position of impurity and number of unit cells involved in NWSLs. Additionally, it is found that binding energies of Sph NWSL are larger than those of Cyl NWSL.