Polarity Reversal of Terahertz Electric Field from Heavily p-Doped Silicon SurfacesSupported by the National Key Research and Development Program of China (Grant No. 2019YFA0307704), the NSAF Joint Fund (Grant No. U1830206), the Major Research Project of National Natural Science Foundation of China (Grant No. 91850201), and the National Natural Science Foundation of China (Grant Nos. 11974426, 11974425, 11874425, 11774428, and

Abstract

Above-band-gap optical excitation of electron-hole pairs screens the doping-induced surface electric field and generates terahertz (THz) pulses via free-carrier transport. THz emission from a heavily doped silicon surface is much weaker than that of lightly doped samples. A polarity reversal of the THz electric field is observed in heavily doped p-type silicon, indicating that the doping related and carrier induced surface electric fields oppose each other. By comparing the penetration depth of the excitation laser with the thickness of the depletion layer for the doped silicon, it is shown that competition between diffusion and drift current causes the polarity reversal.