Terahertz band lying between infrared and microwave is a very promising part of electromagnetic spectrum for spectroscopy, space applications and different kind of imaging applications such as medical and security. Recently, this special band has attracted the attention of communication society because of its huge bandwidth and therefore ability of very high speed wireless communications. One of the challenges still on the table is to obtain efficient terahertz sources. In this paper, recent studies on the topic of efficient terahertz sources are reviewed comparatively. Especially for the communication concept, taking into account the efficiency, it can be said that the trend goes to the optical photoconductive materials method including plasmonic electrodes.