Shuyi Wei

Exciton states in wurtzite InGaN strained coupled quantum dots: Effects of piezoelectricity and spontaneous polarization

Within the framework of the effective-mass approximation, exciton states confined in wurtzite InxGa1−xN∕GaN strained coupled quantum dots (QDs) are investigated by means of a variational approach, including three-dimensional confinement of the electrons and holes in the QDs and strong built-in electric field effects caused by the piezoelectricity and spontaneous polarization. The relationship between exciton states and structural parameters of coupled QDs is studied in detail. We find that the strong built-in electric field in the InxGa1−xN∕GaN strained coupled QDs gives rise to a marked reduction of the effective band gap of InxGa1−xN QDs and leads to a remarkable increasing of the emission wavelengths. Both the sizes and alloy fluctuations of QDs have a significant influence on the exciton states and interband optical transitions in coupled QDs. Moreover, the barrier thickness between the two coupled InxGa1−xN QDs has a considerable influence on the exciton states and optical properties. When the barrie...

Tunable electronic structures of p-type Mg doping in AlN nanosheet

The p-type impurity properties are investigated in the Mg-doped AlN nanosheet by means of first-principles calculations. Numerical results show that the transition energy levels reduce monotonously with the increase in Mg doping concentration in the Mg-doped AlN nanosheet systems, and are lower than that of the Mg-doped bulk AlN case for the cases with larger doping concentration. Moreover, Mg substituting Al atom is energy favorably under N-rich growth experimental conditions. These results are new and interesting to further improve p-type doping efficiency in the AlN nanostructures.

Quantum size effect on excitons in zinc-blende GaN/AlN quantum dot

Within the framework of effective-mass approximation, exciton states confined in zinc-blende GaN/AlN quantum dot (QD) are investigated by means of a variational approach, including three-dimensional confinement of the electron and hole in the QD and finite band offsets. Numerical results show that the exciton binding energy and the interband emission energy are both decreased when QD height (or radius) is increased. Our theoretical results are in agreement with the experimental measurements.

Electron and impurity states in GaN/AlGaN coupled quantum dots: Effects of electric field and hydrostatic pressure

Based on the effective mass approximation, the ground-state donor binding energy of impurity located at the surface of the zinc-blende (ZB) GaN/AlGaN symmetric coupled quantum dots (SCQDs) is investigated variationally, considering the combined effects of the electric field to the right (along the growth direction) and the hydrostatic pressure. Numerical results show that the impurity localized inside the left dot, the donor binding energy is insensitive to the middle barrier width of the ZB GaN/AlGaN SCQDs if the middle barrier width is large. While the hydrostatic pressure increases the donor binding energy for any electric field and impurity position. Moreover, the hydrostatic pressure has a remarkable influence on the donor binding energy of impurity localized inside left dot. In addition, the competition effects between the electric field and hydrostatic pressure (between the electric field and quantum confinement) on the donor impurity states in the ZB GaN/AlGaN SCQDs have also been investigated in ...

Effects of applied electric field and hydrostatic pressure on donor impurity states in cylindrical GaN/AlN quantum dot

Based on the effective-mass approximation and variational procedure, the donor impurity states in the cylindrical zinc-blende GaN/AlN quantum dot (QD) are investigated, considering the influence of the applied electric field and hydrostatic pressure along the growth direction. Numerical results show that the donor binding energy is highly dependent on the impurity positions, quantum size, applied electric field, and hydrostatic pressure. It is found that the hydrostatic pressure has a remarkable influence on the donor binding energy of the hydrogenic impurity in the QD with a small size and a strong applied electric field. However, the applied electric field affects obviously the donor binding energy in the QD with a large QD size and a small hydrostatic pressure. In addition, the competition effects between the applied electric field and quantum confinement on the donor impurity states in the QD have also been investigated in detail, which is useful to understand impurity states in semiconducting nanostr...

Barrier width dependence of the donor binding energy of hydrogenic impurity in wurtzite InGaN/GaN quantum dot

Within the framework of the effective-mass approximation, the barrier width dependence of the donor binding energy of hydrogenic impurity in a cylindrical wurtzite (WZ) InGaN/GaN strained quantum dot (QD) is calculated by means of a variational procedure, considering the strong built-in electric field effect due to the spontaneous and piezoelectric polarizations. Numerical results show that the built-in electric field and the donor binding energy of the impurity located at any growth direction position are obviously dependent on the barrier width in WZ In0.1Ga0.9N/GaN strained QD with a small barrier width ( 8 nm). Moreover, the donor binding energy of the impurity located at the right boundary of the QD is independent of the barrier width with any dot height and indium compositi...

Donor impurity states in wurtzite InGaN staggered quantum wells

Within the framework of the effective-mass approximation, donor impurity states in wurtzite (WZ) InGaN staggered quantum wells (QWs) are investigated theoretically. Numerical results show that the donor binding energy becomes insensitive to the variation of In composition y in the WZ In0.2Ga0.8N/InyGa1−yN staggered QWs when y > 0.125 and for any impurity position. Moreover, for the impurity located at the right edge of the InyGa1−yN well layer, the donor binding energy has a minimum and it is also insensible to the variation of well width in the staggered QWs when the well width L > 3 nm.

Shallow-donor impurity in zinc-blende InGaN/GaN asymmetric coupled quantum dots: Effect of electric field

We have performed a theoretical calculation of the shallow-donor impurity states in cylindrical zinc-blende (ZB) InGaN/GaN asymmetric coupled quantum dots (QDs), considering the effect of the electric field applied to the left (opposite to the growth direction). Numerical results show that the donor binding energy in ZB InGaN/GaN asymmetric coupled QDs is highly dependent on the impurity positions, asymmetric coupled QD structure parameters, and the electric field. In the presence of the electric field, if the left dot height is increased from zero, the donor binding energy of the impurity localized inside the middle barrier layer has a maximum value; if the right dot is increased from zero, the donor binding energy of impurity localized inside the right dot has a maximum value. It is also found that for the impurity located at the center of the right dot, the donor binding energy is insensible to the electric field when the electric field is large; however, the critical electric field is smaller if the r...

Hydrogen chemisorption on contaminated composite catalysts

Abstract The impurity effect on chemisorption of hydrogen on a contaminated supported-metal catalyst is investigated by using the Green function method and the complex-energy-plane integration approach. The tight-binding approximation is employed to model the H Ni/ZnO system. The Anderson-Newns model is used to calculate the chemisorption energy and the adatom charge transfer. It is found that the presence of the impurity Cu(Co) can weaken (strengthen) the chemisorption process and the effect of the impurity is most significant when the impurity atom is closest to the surface.

Effective n-type F-doped MoSe2 monolayers

Using a first-principles method, based on the Vienna Ab-initio Simulation Package (VASP), we have studied the electronic structure, formation energy and transition level of a MoSe2 monolayer doped with V and VII atoms. The numerical results show that the dopant atoms can induce magnetism, except for in the case of the As-doped system. Specifically, N- and F-doped systems exhibit magnetic nanomaterial properties, P- and As-doped systems display metallic features, and in the cases of Cl-, Br- and I-doped systems, the systems exhibit half-metallic ferromagnetism (HMF). The formation energy calculations indicate that this can be more effective for achieving n-type and p-type doped MoSe2 under Mo-rich experimental conditions. However, for the systems doped with group V atoms, the transition level decreases with increasing atomic radius, but that of those doped with VII atoms increases with increasing atomic radius. By comparing the results, we find that the transition level is only 31 meV in F-doped MoSe2 monolayers, which indicates that F impurities can offer effective n-type carriers in MoSe2 monolayers.