Exciton states and optical properties in wurtzite (WZ) InGaN/GaN quantum well (QW) are investigated theoretically, considering finite barrier width and built-in electric field effects. Numerical results show that when the barrier width increases, the ground-state exciton binding energy, the interband transition energy and the integrated absorption probability increase first and then they are insensitive to the variation of the barrier width. For any barrier width, the ground-state exciton binding energy and the integrated absorption probability have a maximum when the well width is 1 nm; moreover, the integrated absorption probability goes to zero when the well width is larger than 6 nm. In addition, the competition effects between the built-in electric field and quantum confinement are also investigated in the WZ InGaN/GaN QW.Highlights► The exciton states and optical properties are insensitive to the larger barrier width. ► The integrated absorption probability gets to zero when the well width is larger ► The competition effects between quantum confinement and built-in electric field are also investigated.

Within the framework of the effective-mass and envelope function theory, exciton states and optical properties in wurtzite (WZ) InGaN/GaN quantum wells (QWs) are investigated theoretically considering the built-in electric field effects. Numerical results show that the built-in electric field, well width and in composition have obvious influences on exciton states and optical properties in WZ InGaN/GaN QWs. The built-in electric field caused by polarizations leads to a remarkable reduction of the ground-state exciton binding energy, the interband transition energy and the integrated absorption probability in WZ InGaN/GaN QWs with any well width and In composition. In particular, the integrated absorption probability is zero in WZ InGaN/GaN QWs with any In composition and well width L > 4 nm. In addition, the competition effects between quantum confinement and the built-in electric field (between quantum size and the built-in electric field) on exciton states and optical properties have also been investigated.Highlights► In composition effects on optical absorption are obvious in InGaN QWs with small well width. ► The integrated absorption probability is zero when well width L > 4 nm for any In composition. ► The competition effects between quantum confinement and the built-in electric field are also investigated.

The effect of electric field on exciton states and optical properties in zinc-blende (ZB) InGaN/GaN quantum dot (QD) are investigated theoretically in the framework of effective-mass envelop function theory. Numerical results show that the electric field leads to a remarkable reduction of the ground-state exciton binding energy, interband transition energy, oscillator strength and linear optical susceptibility in InGaN/GaN QD. It is also found that the electric field effects on exciton states and optical properties are much more obvious in QD with large size. Moreover, the ground-state exciton binding energy and oscillator strength are more sensitive to the variation of indium composition in InGaN/GaN QD with small indium composition. Some numerical results are in agreement with the experimental measurements.Research Highlights►Electric field leads to a reduction of exciton binding energy and oscillator strength. ►Exciton binding energy and oscillator strength decrease with increasing the dot height. ►Exciton binding energy increases with increasing the indium composition. ►Intensity of the linear susceptibilities decreases with increasing the electric field.

Based on the effective-mass approximation, the ground-state donor binding energy in cylindrical zinc-blende (ZB) InGaN/GaN asymmetric coupled quantum dots (QDs) is investigated variationally. Numerical results show that the ground-state donor binding energy is highly dependent on the impurity positions and asymmetric coupled QDs structure parameters. The donor binding energy is distributed asymmetrically with respect to the center of the asymmetric coupled QDs. The position of the maximum value is located inside the wide QD. When the impurity is localized inside the middle barrier layer, the donor binding energy has a maximum value with the variation of any dot height in ZB InGaN/GaN asymmetric coupled QDs. In particular, for the impurity localized inside the wide dot, the donor binding energy is insensitive to large middle barrier width (Lmb≥3nm) in the ZB In0.1Ga0.9 N/GaN asymmetric coupled QDs.

Within the framework of the effective mass, the electric field effect on the optical absorption coefficient is investigated theoretically in cylindrical ZnO quantum wire (QWR). Numerical results show that the application of the electric field can decrease the strength and the threshold energy of the optical absorption coefficient in ZnO QWR. We find that there are additional oscillations in the absorption above the effective band gap, which are due to the Franz–Keldysh effect for the electric field parallel to the axis of the wire. In addition, quantum size effects on the optical absorption of ZnO QWR are also calculated.

Based on the effective-mass approximation, the hydrostatic pressure effects on the donor binding energy of the hydrogenic impurity in zinc-blende (ZB) InGaN/GaN quantum dot (QD) are investigated by means of a variational procedure. Numerical results show that the donor binding energy increases when the hydrostatic pressure increases for any impurity position and QD structure parameter. Moreover, it is found that the hydrostatic pressure has a remarkable influence on the donor binding energy of the hydrogenic impurity located at the vicinity of dot center in ZB InGaN/GaN QD.

The ground-state binding energy of a hydrogenic donor impurity in wurtzite (WZ) GaN/AlGaN coupled quantum dots (QDs) is calculated by means of a variational method, considering the strong built-in electric fields caused by the piezoelectricity and spontaneous polarizations. The strong built-in electric fields induce an asymmetrical distribution of the ground-state binding energy with respect to the center of the coupled QDs. If the impurity is located at the low dot, the ground-state binding energy is insensitive to the interdot barrier width of WZ GaN/AlGaN coupled QDs.

Based on the effective-mass approximation, the hydrostatic pressure effects on exciton states in InAs/GaAs self-assembled quantum dots (QDs) are studied by means of a variational method. Numerical results show that the exciton binding energy has a minimum with increasing dot height for any hydrostatic pressure. The interband emission energy increases when the hydrostatic pressure increases. In particular, we find that hydrostatic pressure has a remarkable effect on exciton states for small QD size. Our results are in agreement with experiment measurements.

Based on the effective-mass approximation, exciton states in wurtzite (WZ) and zinc-blende (ZB) InGaN/GaN coupled quantum dots (QDs) are studied by means of a variational method. Numerical results show clearly that both the sizes and In content of QDs have a significant influence on exciton states in WZ and ZB InGaN/GaN coupled QDs. Moreover, the ground-state exciton binding energy decreases when the interdot barrier layer thickness increases in the WZ InGaN/GaN coupled QDs. However, the ground-state exciton binding energy has a minimum if the interdot barrier layer thickness increases in the ZB InGaN/GaN coupled QDs.

Within the framework of effective-mass approximation, we have calculated the binding energy of a hydrogenic donor impurity in a zinc-blende (ZB) GaN/AlGaN cylindrical quantum dot (QD) using a variational procedure. It is found that the donor binding energy is highly dependent on the impurity position and QD size. The donor binding energy EbEb is largest when the impurity is located at the center of the QD. The donor binding energy is decreased when the QD height (radius) is increased.

Exciton states and optical properties in wurtzite (WZ) InGaN/GaN quantum well (QW) are investigated theoretically, considering finite barrier width and built-in electric field effects. Numerical results show that when the barrier width increases, the ground-state exciton binding energy, the interband transition energy and the integrated absorption probability increase first and then they are insensitive to the variation of the barrier width. For any barrier width, the ground-state exciton binding energy and the integrated absorption probability have a maximum when the well width is 1 nm; moreover, the integrated absorption probability goes to zero when the well width is larger than 6 nm. In addition, the competition effects between the built-in electric field and quantum confinement are also investigated in the WZ InGaN/GaN QW.Highlights► The exciton states and optical properties are insensitive to the larger barrier width. ► The integrated absorption probability gets to zero when the well width is larger ► The competition effects between quantum confinement and built-in electric field are also investigated.

The donor binding energy of the hydrogenic impurity is calculated as functions of the impurity position and structural parameters of wurtzite (WZ) InGaN/GaN quantum dot (QD). Numerical results show that the strong built-in electric field induces an asymmetrical distribution of the donor binding energy with respect to the center of the QD. When the impurity is located at the right boundary of the WZ InGaN/GaN QD, the donor binding energy is insensitive to the dot height, and it is largest when In composition x=0.3 for different WZ InGaN/GaN QD. Realistic cases, including the impurity in the QD and the surrounding barriers.

The effect of electric field on exciton states and optical properties in zinc-blende (ZB) InGaN/GaN quantum dot (QD) are investigated theoretically in the framework of effective-mass envelop function theory. Numerical results show that the electric field leads to a remarkable reduction of the ground-state exciton binding energy, interband transition energy, oscillator strength and linear optical susceptibility in InGaN/GaN QD. It is also found that the electric field effects on exciton states and optical properties are much more obvious in QD with large size. Moreover, the ground-state exciton binding energy and oscillator strength are more sensitive to the variation of indium composition in InGaN/GaN QD with small indium composition. Some numerical results are in agreement with the experimental measurements.Research Highlights►Electric field leads to a reduction of exciton binding energy and oscillator strength. ►Exciton binding energy and oscillator strength decrease with increasing the dot height. ►Exciton binding energy increases with increasing the indium composition. ►Intensity of the linear susceptibilities decreases with increasing the electric field.