External Electric Field Effect On Electronic And Optical Properties In InGaN/GaN Low Dimensional Systems

Within the framework of the effective-mass approximation, external electric field effect on the donor impurity states in zinc-blende (ZB) InGaN/GaN symmetric multiple quantum well (SMQWs) has been investigated variationally by using a hydrogenic trial wave function. In the process of calculations, well widths, inter-well barrier widths, external electric field effect on the donor binding energy have been considered effectively. The main conclusions are given as follows: Donor binding energy of impurity located at the center of left well in ZB InGaN/GaN SMQWs has a maximum value with increasing the well width; however, that of impurity confined inside the middle well and right well decreases monotonically when the well width increases. Donor binding energy of impurity located at the center of left well in ZB InGaN/GaN SMQWs increases and then is insensitive to the increment of the middle barrier width in the presence of external electric field. Donor binding energy of impurity located at the center of each well in ZB InGaN/GaN SCQWs is insensitive to the increment of the external electric field when the external electric field is large. Donor binding energy of impurity located at the center of the left well in ZB InGaN/GaN SMQWs has a maximum value with increasing the external electric field for large well width; moreover, the critical electric field of the maximum value decreases when the well width increases.To investigate variationally the external electric field effect on the exciton states and related optical properties in ZB InGaN/GaN single quantum dot (SQD), a two-parameter Gaussian type trial wave function was used. After explicitly investigating the dot height, quantum confinement, external electric field effect on the ground-state exciton binding energy, interband optical transition energy, ground-state oscillator strength and linear optical susceptibility, the main conclusions obtained are given as follows: exciton binding energy and interband optical transition energy are decreased for any external electric fields with increasing the dot height in ZB InGaN/GaN single quantum dot (SQD). When the external electric field effect is considered, exciton binding energy and interband optical transition energy are decreased sharply when the dot height is increased in ZB InGaN/GaN SQD. In addition, the ground-states oscillator strength is also reduced remarkablely with increasing the dot height in the presence of external electric field. The external electric field effect is more obvious when the dot height of ZB InGaN/GaN is large. The ground-state exciton binding energy and oscillator strength are increased with increasing the Indium concentration in ZB InxGa1-xN/GaN. Moreover, when the Indium concentration is low, the ground-state exciton binding energy is more sensitive to the increment of Indium concentration. When the external electric field is increased, the intensity of ground-state linear optical susceptibility is reduced.To investigate variationally the hydrogenic donor impurity states in ZB InGaN/GaN asymmetric quantum dots, a two-parameter Gaussian type trial wave function was used. The main results can be given as follows. The donor binding energy has a maximum value and it is larger with impurity located inside the wider QD. It is also found that the variation of the height of any dot has a remarkable influence on the donor binding energy in the ZB InGaN/GaN asymmetric coupled QDs. In addition, when the impurity is located inside the wider QD, the donor binding energy is insensible to the middle barrier width for large middle barrier width in the ZB In0.1Ga0.9N/GaN asymmetric coupled QDs.To investigate variationally the electric field effect on the donor impurity in ZB InGaN/GaN symmetric quantum dots, a two-parameter Gaussian type trial wave function was used. After explicitly investigating the dot height, middle barrier width, impurity position and electric field effect, the main results can be given as follows. The donor binding energy has a maximum value and the position of the maximum value is localized inside the right dot of the symmetric coupled QDs structure due to the effect of the electric field. The donor binding energy is decreased with increasing the dot height except that the impurity located at the center of the right QD. In particular, numerical results also show that the donor binding energy is insensitive to the middle barrier width (the electric field) if the middle barrier width (the electric field) is large when the impurity is located at the center of the right dot in ZB symmetric In0.1Ga0.9N/GaN coupled QDs.