Abstract : This Thesis deals with the generation of THz frequencies based on the photomixing process. The first part describes the main components of devices, which are low-temperature-grown GaAs (LTG-GaAs), interdigitated electrodes and planar antenna. This study allows us to obtain a largely tunable source between 100 GHz and 4 THz, suitable to spectroscopic studies. In the second part, two different photodetector's topologies are examined, the first one vertical and the second one distributed. The vertical topology actually permits to alleviate two-dimensionnal effects, which affects its performance and robustness. In order to manufacture a vertical photodetector, a wafer bonding technique has been used during the process. Experimental results show an improvement in photoresponsivity (x3) and in photomixing (x7) compared to planar technology. The other option, i.e. the use of a distributed photodetector, requires a preliminary study of propagation lines at THz frequencies. Boundaries conditions effect is closely look into, and propositions of original transmission lines are brought up. However, the most promising prospect seems to be the operation of our devices at long wavelength (1.5 Μm). Two routes are discussed, which rely respectively on the sub-gap absorption in LTG-GaAs and on the use of a new material (LTG-InGaAs).