| The physical mechanism of the femtosecond laser pulse triggering the semiconductor surface radiation terabera(THz)wave includes:optical rectification effect,photo-onductive antenna,semiconductor surface field effect(material built-in electric field surface depletion layer,Photo-Dember effect.Photo-conductive antennas commonly use Gallium Arsenide(GaAs)to radiate THz waves,and optical rectification effect can be Zinc Telluride(ZnTe).Indium Phosphide(InP)is a highly efficient THz wave source based on the THz wave of semiconductor surface field radiation.The introduction of the Dember electric field found that the Indium Arsenide(InAs)has higher radiation efficiency than InP.Because InAs is not limited by material breakdown voltage during the experimental test of radiated THz wave under the pulse pump of femtosecond laser,the sesarch on radiating THz wave under different structures of this kind of semiconductor material and its surface has attracted more and more attention.The forbidden band width of InAs at 300 K is 0.36 eV,and the THz wave intensity radiated by the photo-generated carriers under the Dember electric field is oner order of magnitude higher than that of the wide band gap semiconductor(GaAs,InP).However,under the bigger of femtosecond laser pulses,the intensity of radiated THz waves is still not ideal,which limits the development of related THz radiation sources.In this paper,focusing on improving the terahertz radiation intensity of InAs surface,firstly,based un the two-dimensional semiconductor optoelectronios module and the continuity equation of semiconductor in the finite element simulation software,the different wrinkle structures on the InAs surface are studied.The internal carrier concentration changes to InAs.The influence of the lateral electric field distribution on the surface,semi-quantitatively obtained the influence of the incident light angle,optical pulse power,spot size and other parameters on the transverse Dember effect radiation THz wave intensity of the InAs surface.Secondly,the InAs surface nude and the surface region were plated with gold by means of ion beam processing(1 keV,flow rate 1×1019 cm-2 Argon(Ar)ion beam bombardment of InAs surface to form ripples)(metal-semiconductor structure(referred to as gold-semi)),horizontal ripples and longitudinal ripples structure,THz wave radiation characteristics under different surface structures were tested by a reflective terahertz time-domain spectroscopy(THz-TDS)system:femtosecond laser pulse vertical trigger the InAs surface nude,the photo-generated carriers are longitudinally distributed,and the radiated THz waves are distributed laterally inside the InAs;if the femtosecond laser pulse triggers the InAs surface(gold-semi structure),the longitudinal ripples,the horizontal ripples of the nude and the gold-semi area,photo-generated carriers are distributed along the surface of InAs surface,so that THz waves with good performance are obtained at the far field of InAs outer surface;the influence of space angles change of photo-detection crystal ZnTe on THz radiation characteristics is investigated;The ratio of the half area is different,and the change of the ZnTe space angles is not obvious for the change of the output waveform.The experimental results show that the femtosecond laser pulse triggers the intensity of the THz wave in the gold-semi region of the InAs surface and the nude region in the same order of magnitude,which provides theoretical and experimental basis for the subsequent gold-semi structure design based on InAs array. |
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