Time-frequency analysis of nonlinear terahertz signals due to hot electrons in the nonparabolic conduction bands of n -doped In0.57Ga0.43As films

Abstract

In this Research Letter, we study the transient carrier dynamics and the nonlinear terahertz effects induced by an intense multicycle terahertz pulse in the $n$-doped semiconductor ${\mathrm{In}}_{0.57}{\mathrm{Ga}}_{0.43}\mathrm{As}$. For incident terahertz pulses with relatively high frequency $\ensuremath{\ge}1$ THz, we reveal the generation of low- and high-frequency components in the transmitted intensity spectra. We study the time emission of these components at different frequencies using the G\'abor transform, showing that the low- and high-frequency components are due to the nonparabolicity of the conduction band. Our results demonstrate that for a multicycle terahertz pulse, we generate a distorted biphasic truncated exponential current with the driving terahertz fields, leading to discrete high-order harmonic generation in the transmitted intensity spectra.