Anisotropic Photoconductivity and Terahertz Emission from Semiconductors

In this report we consider the anisotropic photoconductivity in a semiconductor excited by two-frequency optical radiation, as well as its contribution to the photocurrent at the beat frequency corresponding to the THz region. The interband anisotropic photoconductivity arises due to the anisotropy of the momentum distribution of electrons excited by polarized light and the energy dependence of the momentum relaxation time and effective mass of the electrons. The response time of the anisotropic photoconductivity is very short, since it is determined by the electron momentum relaxation time, which for typical semiconductors is about 200 – 300 fs

Terahertz Pulse Emission from Semiconductor Heterostructures Caused by Ballistic Photocurrents

Terahertz radiation pulses emitted after exciting semiconductor heterostructures by femtosecond optical pulses were used to determine the electron energy band offsets between different constituent materials. It has been shown that when the photon energy is sufficient enough to excite electrons in the narrower bandgap layer with an energy greater than the conduction band offset, the terahertz pulse changes its polarity. Theoretical analysis performed both analytically and by numerical Monte Carlo simulation has shown that the polarity inversion is caused by the electrons that are excited in the narrow bandgap layer with energies sufficient to surmount the band offset with the wide bandgap substrate. This effect is used to evaluate the energy band offsets in GaInAs/InP and GaInAsBi/InP heterostructures

Terahertz Generation from Femtosecond-Laser-Excited GaAs Surface Due to Electric-Field-Induced, Optical Rectification

The dynamics of the depletion field screening induced by photoexcited carriers and THz generation caused by the electric-field-induced optical rectification are simulated for GaAs surface excited by femtosecond laser radiation on the basis of an ensemble Monte Carlo method. The results show that the photocarrier-induced screening occurs on a subpicosecond time scale and THz pulse essentially changes its wave form depending on excitation pulse duration and fluence. The possibility to use the depletion electric field induced THz generation for study of subpicosecond electric field screening dynamics is discussed