The Study Of The Hydrogenic Impurity States In Symmetric Couple Quantum Dots

Recently, the wide-band gap semiconductor heterostructures have attracted much attention due to their conspicuous device applications both in electronics and optoelectronics. Within the frame work of effective-mass approximation, the hydrogenic impurity states in wurtzite (WZ) symmetric ZnO/MgZnO strained coupled quantum dots (QDS) and zinc-blende (ZB) symmetric InGaN/GaN multiple quantum dots (QDS) are investigated by means of a variational approach in this paper.Firstly, the brief introduction of the semiconductor and the quantum dots are discussed in this paper. Meanwhile, the hydrogenic impurity states in the ZnO-based and GaN-based quantum dots have also been presented. The II-VI and III-V nitrides, especially, the ZnO-based and GaN-based nitrides are introduced in this paper later. Moreover,the strain and polarization in the wurtzite structure and the strong built-in electric field induced by the spontaneous and piezoelectric polarizations have also been discussed in detail. Subsequently, the theoretical model of the hydrogenic impurity states in wurtzite symmetric ZnO/MgZnO coupled quantum dots and zinc-blende symmetric InGaN/GaN multiple quantum dots are showed in this paper. Finally, the numerical results and the physical reasons have been analyzed explicitly.Numerical results show that the strong built-in electric field induces an asymmetric distribution of the donor binding energy with respect to the center of the WZ symmetric ZnO/MgZnO strained coupled QDs. Moreover, the donor binding energy is larger when the impurity is located inside the left dot due to the effects of the strong built-in electric field. With increasing the dot height, the donor binding energy has a maximum value when the impurity located at the center of the left dot. When the middle barrier layer width increases, the donor binding energy decreases with increasing the middle barrier layer width when the impurity is localized inside the middle barrier layer and the right dot. For any impurity position, the donor binding energy decreases when the radius increases. In particular, we also find that the donor binding energy is insensitive to the Mg composition with the impurity located at the right boundary of the left dot when the Mg composition x >0.1.It is found that the donor binding energy has a maximum value when the impurity is located at the center of the QDs in the ZB symmetric InGaN/GaN multiple QDS. Numerical results also show that, for the impurity located at the center of the middle QD, the donor binding energy has a minimum value with increase in the middle barrier width. The donor binding energy is insensitive to the increment of the middle barrier width when the middle barrier width is large. In addition, for the impurity located at the center of the QDs, the donor binding energy increases and has a maximum with increase in the dot height. Moreover, we find that the donor binding energy is basically invariable with increase in the In composition when the impurity is located at the center of the middle barrier.