The Study Of Impurity States In Low-dimensional Semiconductor Structures

In recent years,the study of low dimensional semiconductor structures(quantum well,quantum wire and quantum dots et al.)has attracted many attentions for their potential applications in electronic and optoelectronic devices.Impurity in semiconductor optoelectronic devices plays a very important role because the existence of impurity can greatly affect the electronic and optical properties of nanostructures and influences the properties of the corresponding optoelectronic devices.The electronic state in low dimensional semiconductor materials is a basic problem in semiconductor physics.In addition,external electric field and magnetic field can affect physical properties of impurity in low dimensional semiconductor structures.Considering the influence of the electric field and magnetic field,the study of the electronic state can further understand the physical properties of semiconductor materials and the related electronic devices.In this paper,on the basis of existing theoretical research,under the theoretical framework of effective mass envelope function approximation,the plane wave expansion method is adopted to calculate the electronic state in quantum wells,quantum wires,quantum dots and quantum rings,and considering the influence of applied electric field and magnetic field.The details of this article are as follows:1.In the framework of effective mass envelope function approximation,the two common used methods to calculate the electronic state in low dimensional semiconductor structures--variational method and plane wave method are compared.The electronic state in InGaN/GaN square quantum well,cylindrical quantum wire and spherical quantum dot is calculated using two methods.The donor impurity ground state energy calculated by the variational method is approximated,which may be greater than the real value,thus the ground state binding energy of donor impurity calculated by the variational method is smaller than the true value;The ground state energy and ground state binding energy of the donor impurity calculated by the plane wave method are more reliable and closer to the real value.In addition,the electric field effect calculated by the variational method is more obvious.At the same time,the influence factors of the calculation precision of plane wave method are studied.The results show that when the number of plane waves is no less than 13~3 and the barrier width(BW)is2a~*?BW?4a~*,the calculation results are more stable.2.The influences of quantum well shape,applied electric field and magnetic field on the binding energy of donor impurity are compared in InGaAsP/InP square shaped,parabolic shaped and V-shaped quantum wells.Under the theory of effective mass envelope function approximation,the ground state binding energies of donor impurity as functions of quantum well width,impurity position,the electric field and magnetic field strengths are calculated in the three shape quantum wells by the plane wave expansion method.The numerical results show the ground state binding energy as a function of the quantum well width,when the quantum well width is smaller,impurity binding energy is larger in square quantum well;when the quantum well width is bigger,impurity binding energy is larger in V-shaped quantum well.When the quantum well width is fixed(W=2a~*)and the impurity is located at the vicinity of the quantum well center,the donor impurity binding energy is the largest in V-shaped quantum well;when the impurity is located at the edge of quantum well,and the donor impurity binding energy is the largest in square quantum well.When the quantum well width is larger,the electric field effect in square quantum well is the most obvious;and when quantum well width is smaller,the electric field effect in V-shaped quantum well is the most obvious.The influence of magnetic field on impurity binding energy in V-shaped quantum well is the most prominent.In addition,the combined effects of electric and magnetic fields are consistent in different shaped quantum wells.3.We use the plane wave expansion method to calculate the ground state binding energy of hydrogen donor impurity in InGaAsP/InP ring quantum well wire,and analyze the influences of external electric field and magnetic field on the ground state binding energy.The results show that when the impurity moves along the radius of the quantum wire,the ground state binding energy can reach the maximum at the center of the inner radius and the outer radius.When the inner(outer)radius is fixed,the binding energy is nonlinear change with the increase of outer(inner)radius.In addition,the axial electric field makes the impurity binding energy decrease,while the transverse magnetic field makes the impurity binding energy increase.The reduction of impurity binding energy caused by the external electric field can be compensated by the introduction of a certain strength of magnetic field.4.The influences of electric field and magnetic field on the ground state binding energy are studied in InGaAsP/InP core-shell quantum dot through the plane wave expansion method.And the influences of the shell thickness,core radius,location of impurity on the ground state binding energy of donor impurity are analyzed.Numerical results show that the binding energy decreases with the increase of core radius.When the thickness of shell is just beginning to increase,the impurity binding energy also increases;when the shell thickness increases to a certain value,the binding energy will no longer change.The external electric field changes the symmetric distribution of impurity binding energy,and has the least influence on the on-center impurity binding energy.The impurity binding energy still keeps the symmetric distribution when the magnetic field is applied.The binding energy only increases with the increase of magnetic field,while the magnetic field has the greatest influence on the on-center impurity binding energy.5.The plane wave expansion method is used to calculate the hydrogen donor impurity ground state binding energy in InGaAsP/InP quantum ring.The dependence of ground state binding energy on the outer radius,height,impurity position,the electric field and magnetic field strength are analyzed in detail.The impurity binding energy is nonlinear change with the increase of outer radius and ring height.When the donor impurity moves along the axial or radial direction,the ground state binding energy can reach a maximum near the center of height or the center of inner and outer radius.In addition,the combination of impurity position and electric field direction determines the change trend of donor impurity binding energy with the increase of the electric field strength.The differences of binding energy for the impurity located at the symmetric position increase with the increase of electric field strength.The impurity binding energy increases as the magnetic field strength increases,and the influence of magnetic field on impurity binding energy is more obvious along the direction of magnetic field.6.Within the framework of effective-mass envelope-function theory,the ground state binding energy of a hydrogenic donor impurity is calculated in InGaAsP/InP concentric double quantum rings(CDQRs)using the plane wave method.The effects of geometry,impurity position,external electric field and alloy composition on binding energy are considered.It is shown that the peak value of binding energy appears in each ring with larger gap as the donor impurity moves along the radial direction.And the binding energy reaches the peak value at the center of ring height when the donor impurity moves along the axial direction.The binding energy shows nonlinear variation with the increase of ring height.With the external electric field applied along the z axis,the binding energy of donor impurity located at z_i?0 decreases while that located at z_i<0 increases.In addition,the binding energy decreases with increasing Ga composition but increases with increasing As composition.