Pump fluence dependence of ultrafast carrier dynamics in InSb measured by optical pump–terahertz probe spectroscopy

Ultrafast carrier dynamics in intrinsic and n-doped InSb crystals were studied by time-resolved terahertz spectroscopy using an optical pump-terahertz probe setup with pump fluence from 32 μJ/cm2 to 1910 μJ/cm2. With photoexcitation at 800 nm, the ultrafast photoinduced absorption and carrier recovery process of intrinsic and n-doped InSb showed strong pump fluence dependence. It was found that the magnitude of photoinduced absorption first increased and then decreased with pump fluence. The carrier recovery process could be well fitted with a single exponential curve at low pump fluence, but could be well fitted with a biexponential curve at high pump fluence when a fast photocarrier relaxation appeared. The magnitude of photoinduced absorption increased gradually at low pump fluence due to the increase of the carrier at the bottom of the conduction band by impact ionization. The magnitude of photoinduced absorption decreased gradually at high pump fluence, possibly due to the efficiency of transient Auger recombination greater than the rate of carriers generated in the impact ionization process. The fast decay process appearing at high pump fluence was thought to be dominated by transient Auger recombination.