Terahertz radiation and second-harmonic generation from InAs: Bulk versus surface electric-field-induced contributions

Polarized second-harmonic generation and terahertz radiation in reflection from (100), (110), and (111) faces of n-type InAs crystals are investigated as a function of the sample azimuthal orientation under excitation from femtosecond Ti:sapphire laser pulses. The expressions describing the second-order response (optical second-harmonic generation and optical rectification) in reflection from zinc-blende crystals, such as InAs, are calculated taking into account the bulk electric-dipole contribution and the first-order surface electric-field-induced contribution. It is shown that the two contributions can be separated based on rotation symmetry considerations. Moreover, a direct comparison of the second-harmonic generation and terahertz radiation emission indicates that the observed dominant surface electric-field-induced optical rectification component may be attributed to the large free-carrier contribution to the third-order susceptibility in InAs.