The possibility of terahertz generation has been investigated from a photoconductive switch based on GaAs, gated by a femtosecond laser. The emission properties of photoconductive antenna (PCA) with low-temperature-grown (LT) GaAs have been studied. In such GaAs materials presence of the charged defects induces a redistribution of the electric field between the antenna electrodes. This effect has a huge influence on the amplitude of the radiated terahertz field. In this work we demonstrate that carrier concentration enhances radiation power. Results obtained as a function of the laser excitation power (with 100 fs rise time and 1KHz repetition rate) and carrier concentration are discussed and a comparison of the performance of these devices with a conventional antenna-type (dipole) emitter is given. پرونده مقاله