Terahertz-field-induced carrier generation in B i1-x S bx Dirac electron systems

Abstract

Terahertz-field-induced carrier generation processes were investigated in Dirac electron systems, single-crystalline bismuth antimony alloy thin films (Bi1-xSbx; 0≤x≤0.16). This investigation was performed by precisely tuning, via the substituent ratio x, the band structure of the films from that associated with a semimetal to that characteristic of a narrow-gap semiconductor. Terahertz-field-induced absorption was clearly observed within a few picoseconds after the terahertz pump-pulse illumination of Bi1-xSbx semimetal and semiconductor samples. The field-strength dependence of the induced absorption was compared with the calculated Zener tunneling probability in the Dirac-like band dispersion. Through this comparison, the mechanism of the induced absorption was attributed to the carrier generation via the terahertz-field-induced Zener tunneling. The tunneling occurred in subpicosecond timescales even at room temperature, demonstrating that Bi1-xSbx thin films are promising for future high-speed electronics and the investigation of universal ultrafast tunneling dynamics.