  We demonstrate here an efficient THz source with low electrical power
consumption. We have increased the maximum THz radiation power emitted from
SI-GaAs based photoconductive emitters by two orders of magnitude. By
irradiating the SI-GaAs substrate with Carbon-ions up to 2 micron deep, we have
created lot of defects and decreased the life time of photo-excited carriers
inside the substrate. Depending on the irradiation dose we find 1 to 2 orders
of magnitude decrease in total current flowing in the substrate, resulting in
subsequent decrease of heat dissipation in the antenna. This has resulted in
increasing maximum cut-off of the applied voltage across Photo-Conductive
Emitter (PCE) electrodes to operate the device without thermal breakdown from
~35 V to > 150 V for the 25 micron electrode gaps. At optimum operating
conditions, carbon irradiated (10^14 ions/cm^2) PCEs give THz pulses with power
about 100 times higher in comparison to the usual PCEs on SI-GaAs and
electrical to THz power conversion efficiency has improved by a factor of ~
800.
