  We study the effect of a surface modification at the interface between
metallic electrodes and semiconducting substrate in Semi-Insulating GaAs
(SI-GaAs) based photoconductive emitters (PCE) on the emission of Tera-Hertz
(THz) radiation. We partially etch out 500 nm thick layer of SI-GaAs in grating
like pattern with various periods before the contact deposition. By depositing
the electrodes on the patterned surface, the electrodes follow the contour of
the grating period. This increases the effective contact length of the
electrodes per unit area of the active regions on the PCE. The maxima of the
electric field amplitude of the THz pulses emitted from the patterned surface
are enhanced by up to more than a factor 2 as compared to an un-patterned
surface. We attribute this increase to the increase of the effective contact
length of the electrode due to surface patterning.
