Research On Exciton State And Impurity State In ZnO/MgZnO Low-dimensional Structure

Low-dimensional semiconductor nanomaterials have unique characteristics.Consequently,they have broad application prospects in many fields such as optoelectronics,magnetism,nanoelectronics,biology,medicine and so on.Since the exciton effect in low-dimensional nano-semiconductors profoundly affects the properties of materials in terms of light absorption,luminescence,and recombination,and the impurities will largely affect the electrical and optical physical properties of semiconductor materials.Therefore,it is of great significance to study the exciton states and impurity states in low-dimensional semiconductor materials theoretically.Based on the theory of effective mass envelope function,this thesis studies the exciton states and impurity states in the low-dimensional structure of Zn O/Mg_xZn_1-xO using the shooting method and variational method.The main contents are as follows:1.The low-dimensional semiconductor materials and zinc oxide are introduced briefly,mainly from the concepts,fundamental characteristics and device applications,and described the exciton and impurity in low-dimensional semiconductors and their research significance.2.Based on the effective mass and envelope function approximation theory,in low-dimensional semiconductors,the fundamental methods for the study of exciton states and impurity states by shooting method and variational method are introduced in detail.3.The exciton states in different Zn O/Mg_xZn_1-xO low-dimensional structures are studied,including single quantum well,double quantum well,triangular quantum well,cylindrical quantum wire and spherical quantum dot structures.The effects of low-dimensional structures size and Mg composition on the wave functions,exciton Bohr radius,exciton binding energy in different Zn O/Mg_xZn_1-xO low-dimensional structures are analyzed.The results indicate that the exciton binding energy in the square single quantum well,triangular quantum well,cyclindrical quantum wire and spherical quantum dot structures increase initially and decrease afterwards with the increase of the low-dimensional structures size.While the exciton binding energy of the double quantum well structure both have a minimum and a maximum value and the minimum value appear when the widths of the two wells are equal,and eventually tend to a single quantum well as the well width increases.In addition,the results show that the exciton binding energy increases with the increase of Mg component,and the stability is enhanced.4.The exciton states in different Zn O/Mg_xZn_1-xO low-dimensional structures under electric field are studied.Discussed the effect of the applied electric field on the binding energy of excitons in different low-dimensional structures and analyzed the influence of the electric field on the quantum confinement potential and the Bohr radius of the exciton.The results show that the electric field tilts the quantum confinement potential,changes the symmetrical distribution of electrons,and accelerates the dissociation of exciton.For low-dimensional semiconductor structures of arbitrary shapes,the calculations indicate that the application of electric field will reduce the binding energy of excitons.For the low dimensional semiconductor structure with quantum well(quantum wire or quantum dot)structure,after the electric field applied,the exciton binding energy increases rapidly to the peak value and then decreases with the well width(radius of quantum wire or quantum dot)and the decreasing range increases with the increase of the electric field intensity.If the electric field is very large,the exciton effect in the low-dimensional semiconductor structure is invalid due to the ionization of the electric field,resulting in a smaller exciton binding energy and a larger change in the uncorrelated probability,which affects the stability of the exciton.5.The influence of the external magnetic field on the internal exciton states of the Zn O/Mg_xZn_1-xO low-dimensional structure is discussed,and the impact of the external magnetic field on the quantum confinement potential,wave function,exciton binding energy and uncorrelated probability is analyzed.The results indicate that the external magnetic field adds an additional limiting potential on the electrons and holes in the low-dimensional semiconductor structure,reducing the electron cyclotron radius.The magnetic field does not change the symmetrical distribution of electrons in the low-dimensional structure,but only increases the probability of electron distribution.For different low-dimensional structures,the change trend of the exciton binding energy after the application of a magnetic field is similar,the increase increases with the increase of the magnetic field intensity.In addition,the study found that the influence of the applied magnetic field on the uncorrelated probability is very different from that of the applied electric field,just increases the value slightly.6.The electron states of the donor impurity in different Zn O/Mg_xZn_1-xO low-dimensional structures are studied.The impact of the low-dimensional structure size,Mg composition,and donor impurity position on the electronic ground state energy and the binding energy of the donor impurity are discussed.Studies have shown that the electron ground state energy and donor impurity binding energy increase with the increase of Mg composition.Regardless of the presence or absence of impurities,the electron ground state energy decreases with the increase of the structure size.The binding energy of the donor impurity increases rapidly to a maximum value and then slowly decreases to a stable value as the width of the quantum well increases.As the donor impurity moves in the direction of quantum well growth,we find that the confinement energy of the donor impurity is in the quantum well.The maximum value appears in a small range near the center of the quantum well.In addition,studies have found that when the donor impurity is located in the center of the quantum well,the external electric field has a small effect on the binding energy of the donor impurity near the center of the quantum well,but has a greater effect on the binding energy of the donor impurity at the place where the well width is large and the well width is small.In comparison,the electric field does not change the position of the maximum value of the donor impurity binding energy greatly,and it remains in a very small range at or near the center of the quantum well.