Determination of the terahertz pulse emitting dipole orientation by terahertz emission measurements

Terahertz pulse emission from the photoexcited semiconductor surface heavily depends on the orientation of the photo-induced electric dipole. Two methods to determine the orientation of the terahertz pulse emitting dipole have been demonstrated. Method I relies on the measurement of THz emission dependencies on the angle of incidence in the transmission geometry, while method II is based on the measurements of THz emission in the reflection geometry. Theoretical reasoning for both of these methods has been presented. Both of these methods have been tested with a semi-insulating GaAs substrate using an external magnetic field in order to change the tilt angle of the electric dipole. The investigation presented in this work leads to an assumption that the magnetic field induced change in the dipole tilt angle is proportional to the mobility of electrons. Thus, the suggested method may become a promising tool for testing the quality of substrates and epitaxial layers.