Optical Absorption Of Impurity Inter-substate Transitions In Mg_xZn_1-xO/ZnO/Mg_yZn_1-yO Quantum Wells With Mixed Phases

By brief introducing in this thesis the research development and existed problems of the optical absorption of electron,exciton,and impurity state transitions,and particularly pointing out the insufficiency of the discussion about asymmetric structures and the mixed-phase Mg_xZn_1-xO(0.37<x<0.62),the contents of this thesis are introduced about optical absorption of impurity inter-substate transitions in asymmetric Mg_xZn_1-xO/Zn O/Mg_yZn_1-yO quantum wells with mixed phases.Firstly,with consideration of built-in electric fields and the Hartree potential in the thesis,the electron energy levels are obtained by using the finite element difference method,then the impurity substate energy levels are obtained by combination the numerical computation with a variational method to calculate the binding energies of impurity states.Then,the linear and nonlinear optical absorption coefficients(OACs)in wurtzite and zinc-blende structures quantum wells are obtained by using the density matrix method taking into account of electron transitions from the ground impurity substate to the first excited impurity substate and to the second excited impurity substate,respectively.Finally,the binding energy and OACs of electron transitions between the impurity substates in mixed phases are obtained by fitting with the weight model to discuss the effects of ternary mixed crystal within a wide range Mg component,well width,doping density,and light intensity,at the same time,the comparisons with that of electron inter-subband transitions are also given.It is found that the influences of built-in fields to incline the conduction bands are more obvious than that of Hartree potential to bend the bands in the two structures.Within the mixed-phase range,the binding energies of impurity states at wide wells are more sensitive to the variation of the Mg component,besides,there are two peaks with different wavelengths for OACs of the electron transitions between the impurity substates to respond the optical absorption.The nonlinear effect weakens the amplitudes of total absorption peaks but increases their half-height widths.Both of well width and Mg component can adjust the transition energies between impurity substates,and the decrease of Mg component in the right barrier and increase of the well width result in blue shifts of the peaks.The increase of the doping density and decline of the incident light intensity can enhance the transition possibility between impurity inter-substates and improve the efficiency of light absorption.The zine-blende structures dominated peaks are more sensitive to the light intensity,and the total light absorption peak splits into two peaks when the incident light intensity is strong enough.In addition,compared with the peaks of electron inter-subband transitions,the peak position of impurity inter-substate transitions present a blue shift and its amplitude increases.Our results can give guidance for improving the design of relative experiments and preparing the infrared light photodetectors for ZnO/MgZnO quantum wells.