Impurity State And Exciton State In Nitride Semiconductor GaN/Al_xGa_1-xN Quantum Dots Heterostructure And Effects Of Hydrostatic Pressure

Based on the continuous dielectric model and the effective mass approximation,the binding energies and optical properties of impurity and exciton states of GaN/AlxGa1-xN core/shell and inverted core/shell quantum dots under hydrostatic pressure are studied theoretically by using the variational method.Firstly,the binding energy of AlxGa1-xN/GaN inverted core/shell quantum dots is calculated with the change of core size,shell size,A1 component and impurity position.Secondly,the binding energies and photoionization cross sections of impurity states of GaN/AlxGa1-xN core/shell and inverted core/shell quantum dots under pressure are studied.Finally,the binding energies and optical properties of exciton states of GaN/AlxGa1-xN core/shell and inverted core/shell quantum dots are compared.The binding energy and photoionization cross section of the impurity state,the binding energy of the exciton state,the optical absorption coefficient and the radiation lifetime are calculated,respectively.The results show that:1.The impurity state binding energy of the inverted core/shell QDs decreases monotonically with the increase of the radius(core and shell size)of the QDs.When the distance between the center of the quantum dot and the impurity position d increases,the binding energy of the impurity states increases first and then decreases,and there is a maximum value.The binding energy of the impurity states is greatly affected by the location of the impurity with the change of the Al component,showing different trends,and the change is obvious.2.It is shown that the binding energy decreases monotonously with the core size at different impurity locations for GaN/AlxGa1-xN core/shell quantum dot by comparing the noncentral impurity states of GaN/AlxGa1-xN core/shell and inverted core/shell quantum dots.In contrast,for the inverted core/shell quantum dot,the binding energy exhibits different trends with the increase of core size at different impurity locations.But the binding energy decreases monotonically with the shell size for both of them.Moreover,when the photon energy is approximately equal to the donor binding energy,the peak of the photoionization cross section appears.There will be different peak shifts under different conditions,and its peak intensity increases with the increase of core and shell sizes.When the hydrostatic pressure is applied,the binding energy and the peak strength of the photoionization cross section increase with the increase of the pressure.3.By calculating the exciton state binding energy and the photoelectric properties of the two models,the following conclusions are obtained:The change trend of binding energy is the same as that of radiation lifetime,both of which increase first and then decrease with the increase of core size for GaN/AlxGa1-xN core/shell structure.The binding energy decreases first and then increases with the increase of core size,and the change trend of radiation life varies with the change of core size under different shell sizes for inverted core/shell structure.When the photon energy is approximately equal to the binding energy for above two structures,a peak appears in the absorption coefficient,and there will be different peak shifts under different conditions.