Ričardas Norkus, Andrius Arlauskas, Arūnas Krotkus
http://iopscience.iop.org/article/10.1088/1361-6641/aac5a4
Investigation of terahertz (THz) pulse generation from semi insulating and n type InP crystals surfaces is presented in this letter. In order to determine energy separation between the main and subsidiary conduction band valleys, THz pulse amplitude dependences on the photoexcitation wavelength (in a range of 410 – 950 nm) were measured. These dependences had a clear maximum at ~540 nm, which was used to determine the intervalley energy separation in the conduction band of InP as equal to 0.75 eV. Moreover, THz generation mechanisms in InP surface were investigated by additionally analysing the azimuthal angle dependences of the emitted THz signal amplitude and power. It has been shown that the main physical mechanism of the surface THz emission is spatial separation of photoexcited electrons and holes, which can also lead to a symmetry similar to the second-order optical non-linearity. Photocurrent surge in the surface electric field can also contribute to the THz emission from a semi-insulating crystal illuminated by optical pulses with wavelengths close to the absorption edge.
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