Terahertz (THz) emission from ZnSe and ZnTe nano dots and nano gratings is experimentally studied compared with that
from <111> orientation bulk ZnSe and <110> orientation bulk ZnTe. These nano dots and nano gratings are fabricated by
the femtosecond laser ablation technique. Three main mechanisms coexist in the THz radiation from ZnSe and ZnTe
surface nano structures as the same as from bulk sample: current surge effect (drift current), Photo Dember effect
(diffusion current), and optical rectification. Moreover, it is found that nano structures not only contribute to an
enhancement of THz emission, but also increase the threshold of polarity reversal of THz wave, and widen the spectrum
of THz radiation. We also observe a two-fold symmetry in rotating pump polarization angle from ZnTe nano gratings,
which is completely different from the three-fold symmetry observed from bulk ZnTe.