Effect Of Terahertz Laser Field On Photoelectric Properties Of Low Dimensional Semiconductor Materials

The optical and electrical properties of low dimensional semiconductor systems are strongly affected by the applied electric and magnetic fields.Under the action of the applied electric and magnetic fields,they show many interesting physical effects and phenomena,and have been widely used in practical optoelectronic devices.The case of external DC(or low-frequency)electric field and magnetic field has been deeply studied,but the research on the case of external terahertz high-frequency electric field and magnetic field has just begun.In this thesis,the electronic and optical properties of low dimensional semiconductor materials under the action of terahertz laser field are studied theoretically,and some physical effects and phenomena observed are found and explained.The research work and main achievements are as follows:Based on the effective mass approximation,the master equations of multi-level quantum wells,quantum wires and quantum dots under terahertz laser field are established.Using coordinate transformation and a numerical implementation technology,the steady-state energy levels and wave function distributions of quantum wells,wires and dots under strong terahertz laser radiation are calculated,and the effects of strong terahertz laser field on energy level gap and dipole transition matrix elements are analyzed.The observed phenomena are clearly explained by the decorated state images of the interaction system between electrons in quantum wells,lines and points and external laser field.Based on the density matrix theory and iterative method,the analytical expressions of the changes of optical absorption coefficient and photorefractive index of the composite system composed of semiconductor quantum wells,wires and dots and terahertz laser field are derived.The optical coefficients of the system under different parameters are calculated,and the effects of various characteristic parameters of terahertz laser field on the optical properties are discussed.The research shows that terahertz laser field will greatly change the optical characteristics of semiconductor quantum wells,lines and points,and greatly enhance the absorption of low-frequency light,and the absorption of high-frequency light can be realized by adjusting laser parameters.At the same time,in the process of modulating quantum wires and dots,there will be wave function distribution and exchange,and many physical effects such as "forbidden band" in the modulation frequency band.These effects and phenomena not only have rich physical connotation,but also have important application potential for the development of the next generation of new optoelectronic devices at terahertz frequency,such as electro-optic modulator and wavelength division multiplexer.