Surface THz emission from germanium

Terahertz emission from germanium after femtosecond laser pulse excitation is a result of the photo-Dember effect and the built-in surface electric field. The indirect band gap semiconductor is investigated with various excitation wavelengths and different dopant types to differentiate these mechanisms. THz pulse emission is observed even at exciting quanta energies lower than the direct band gap. The azimuthal angle dependences suggest a 3
^rd
order optical nonlinearity.