Investigation On Polarized Photocurrent In Semiconductor Quantum Wells And Organic Thin Films

At present,the requirements for the high performance of materials make the research on the spin characteristics more and more important.The polarized photocurrent effect is a physical phenomenon closely related to spatial or temporal inversion asymmetry,and it is an effective method for characterizing the physical properties of spin correlation.This thesis mainly studies the polarization current in semiconductor quantum wells and organic thin films.The paper is divided into three parts: The first part is the research of spin-emitting diodes composed of CoFeB/MgO ferromagnetic electrodes and semiconductor quantum wells.The polarization currents of the in-plane polarized and out-of-plane polarized spin-emitting diodes are studied,respectively;The second part is the study of the circularly polarized photocurrent in undoped InGaAs/AlGaAs multiple quantum wells.The spin transport process influenced by the in-plane electric field is studied;the third part is the preliminary study of the polarized photocurrent in the organic film,and compared with the polarized photoluminescence spectrum.The main research results are as follows:1.We studied the structure of a spin-emitting diode composed of a CoFeB/MgO ferromagnetic electrode and a GaAs quantum well,and we measured the circular polarization-polarized photocurrent at room temperature.Through the study of the angularly polarized photocurrent of the spin LED,we found that the circularly polarized polarized photocurrent is related to the incident light and the polarization direction of ferromagnetic electrodes.Based on the spin-filter effect of ferromagnetic electrodes,we propose a phenomenological theoretical model to verify the accuracy of the measurement,which is measured in in-plane polarized samples,and generalize the measurement of magnetic moments by circularly polarized photocurrents to the ferromagnetic electrode with three-dimensional magnetic moment.The theoretical model fits well with the experimental results.2.The circularly polarized photocurrents are used to study the in-plane polarization and out-of-plane polarization spin-emitting diodes,we found that the spin polarized photocurrents of different polarization directions have different dependence on the magnetic field,electric field and temperature.In the study of magnetic field,the circularly polarized photocurrent exhibits hysteresis loop characteristics,which verifies the spin filtering effect of ferromagnetic electrodes;Through the study of electric field dependence,we find that the electric field dependence of the circular polarization is related to the polarization direction of the ferromagnetic electrode.By discussing the reasons and calculating the analysis,it is found that the difference observed in the experiment may be derived from Spin relaxation anisotropy;More intrinsic information related to spin physics is obtained through the study of temperature dependence,but due to the complexity of the temperature dependence,further work is required to elucidate this point.3.The undoped InGaAs/AlGaAs multiple quantum wells were investigated by circularly polarized photocurrent.On the one hand,the anisotropic spin splitting in undoped InGaAs/AlGaAs multiple quantum wells is studied by the circularly polarized photocurrent,which is related to the angle.It is speculated that the spin splitting may be derived from the stress.On the other hand,the effects of different oriented electric fields on spin transport are systematically studied by circularly polarized photocurrent.It is found that the different oriented electric fields have different effects on spin transport.Through calculation,we speculate that the dominant mechanism of electric field in different directions is different in spin relaxation.The experimental phenomena are well explained by the hot phonon effect and Rashba effect.4.Through the study of the intrinsic physical mechanism of organic materials.We have found interesting experimental phenomena,which is different from those reported in the literature.Through theoretical analysis,we optimized the experimental configuration to accurately measure the linearly polarized photocurrents and circular polarization photocurrents.Combined with the polarization photoluminescence spectroscopy,it is presumed that the difference signal may be derived from the singlet and triplets related physical processes.At the same time,we have studied the relationship between the polarization current and the voltage in organic thin films,and find that the difference of polarization current has a nonlinear tendency with voltage.