Helium-like donors in semiconductor quantum dots

Abstract

We carry out detailed studies of charged (D+) and neutral (D0) impurity states of helium-like donors in spherical semiconductor quantum dots using both the density functional-effective mass and tight-binding formalisms. We find the two sets of results to be consistent with each other down to very small size quantum dots. We vary the shape of the confining potential, taking it to be square, harmonic and triangular. Independent of the confining potential, we observe a shallow to deep transition of the donor level as the dot size is reduced. However, on further reduction of the size the donor level tends to become shallow again. This suggests that carrier ‘freeze out’ is a distinct possibility for both D+ and D0. Further, optical gaps also show similar behaviour with the size of the dot.

Defects in semiconductor nanostructures

“…As we have mentioned earlier, the HS scheme has self-interaction correction built-in, hence it calculates very good eigenvalues for small number of electrons. This enables us to study optical transition energies as well (see figures 3 and 4 of [16] and figure 3 of [17]). We have also observed SHADES behaviour for the helium-like double donor in SN (see figure 2 of [17]).…”

“…This enables us to study optical transition energies as well (see figures 3 and 4 of [16] and figure 3 of [17]). We have also observed SHADES behaviour for the helium-like double donor in SN (see figure 2 of [17]). The helium-like double donor case will be discussed critically in §4.…”

Shallow–deep transitions of neutral and charged donor states in semiconductor quantum dots

“…The corresponding Hamiltonian and related units have been reported elsewhere. 10 In order to study the shape dependence of binding energy, we model 11,12 the external potential as…”

“…Elaborate tight binding calculations on neutral donor also indicate SHADES behavior. 10 The donor impurities in the present work are located at the center of a spherical quantum dot. It would be interesting to carry out investigations in which the shape of the QD is varied and the donor is moved off center.…”

Entanglement in S states of two-electron quantum dots with Coulomb impurities at the center

“…Few attempts have been made recently towards investigating the effect of a Coulomb impurity on the properties of quantum dots [19][20][21][22]. The systems of confined helium atoms and helium ions that are closely related to quantum dots with a Coulomb impurity have received much attention in recent years [23][24][25][26][27][28].…”