Spectral dependencies of THz pulse emission from GaSb

THz excitation spectroscopy was used to investigate doped (100) GaSb surfaces. THz pulses were generated using excitation photon energies ranging from 0.6 eV to 1.2 eV. Distinct THz generation mechanisms were identified for p- and n-doped samples: the photo-Dember effect and drift current in the surface field, respectively. Moreover, the THz pulse amplitude exhibited azimuthal angle dependence, which arises from non-parabolicity in the Γ valley at low excitation photon energies. When the excitation energy exceeds 0.82 eV, a polarity shift in the azimuthal angle dependence is attributed to carrier scattering into the higher-lying subsidiary L valley.