| Gallium arsenide(GaAs)is one of the best materials for the fabrication of terahertz(THz)photoconductive devices.Studying on the effects of gallium arsenide on the photoelectric properties and carrier ultrafast dynamics in the THz band has a very important significance for optimizing the performance of GaAs materials and developing high-performance photoconductive THz devices.In recent years,the research on GaAs materials using THz technology has been limited to the low frequency(less than 3 THz).In this paper,the technology of THz time-domain sp.ectroscopy(THz-TDS)and optical-pump THz-probe(OPTP)are used in this paper.The photoelectric properties and the ultrafast kinetics of carriers of two typical GaAs samples and the photo-absorption bleaching of GaAs materials are studied in the frequency range of 1-6THz for the first time.The main work is as follows:(1)The photoelectric properties of GaAs material in wide THz band are studiedThe spectral characteristics and photoelectric properties of two typical GaAs materials in the wide THz band are studied based on the THz-TDS technology.The complex transmittance,refractive index,extinction coefficient,absorption coefficient,dielectric constant,dielectric loss,conductivity and other optical parameters of semi-insulating gallium arsenide(SI-GaAs)and low temperature gallium arsenide(LT-GaAs)are acquired in the frequency range of 1-6THz,and the photoelectric properties of the two kinds of GaAs samples are compared.In the spectrum of 1-6THz,it is found that SI-GaAs and LT-GaAs samples have high transmittance and very low dielectric loss for THz wave;the refractive index increases slowly with the increase of frequency,the average values are 3.71 and 3.58,respectively,the conductivity increased with the increase of frequency,and the increase of conductivity of LT-GaAs is relatively large,in the order of 10-1S/cm.The Lorentz dispersion model is used to analyze the photoelectric parameters of SI-GaAs and LT-GaAs.It is found that the experimental results are in good agreement with the theoretical simulation values.(2)The study of ultrafast carrier dynamics of GaAs material in the wide THz bandThe ultrafast kinetic characteristics of two typical GaAs materials in the wide THz band are studied by the OPTP technology.The conductivity and carrier lifetime of SI-GaAs and LT-GaAs at different pump intensities have measured in the frequency range of 1-6THz;the variation of concentration and conductivity of carriers in the relaxation process with time is studied,and the relationship between relaxation time and pumping light intensity is also investigated.The kinetic parameters such as carrier concentration,migration rate and average scattering time of SI-GaAs samples are obtained by using the Drude-Smith model theory to fit the experimental results.It is found that the LT-GaAs material has higher resistivity and faster response speed than the SI-GaAs material in the case of optical pumping.(3)The photo-absorption bleaching of GaAs material materials are studied in strong THz electric fieldThe absorption bleaching of SI-GaAs materials in the strong THz wave field under the condition of optical pumping is studied by using the OPTP technique.It is found that when the pump light intensity is constant,SI-GaAs samples of strong THz field show strong absorption bleaching;the absorption of THz field samples of SI-GaAs bleaching rate is studied,and conditions of the absorption bleaching and the variation of the absorption bleaching rate with the pump light intensity are obtained.The mechanism of absorption bleaching is studied,and the absorption bleaching phenomenon is caused by a strong THz electric field pulse which inducted valley scattering of semiconductor light-stimulated carrier condition between the ? energy valley and L energy valley in a certain pump light,which is related to the strength of the pump light and THz electric field;the absorption and bleaching of terahertz waves in strong electric field by SI-GaAs material is studied by theory of ultrafast carrier dynamics. |
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