Résumé
Nowadays high frequency electronics uses two distinct families of semiconductors-based transistors: field effect transistors and heterojunction bipolar transistors (HBTs). They compete reaching impressive cut off frequencies going up to THz range. Except their usual functions related to switching and amplifying of current or voltage both have been demonstrated as efficient direct THz radiation detectors. Indeed, both types of the transistors have shown that once equipped with antennas, they can capture THz radiation from the open space and deliver the voltage/current proportional to incoming THz radiation power (THz rectification).Most of the work was dedicated to the field effect transistors that rectify THz radiation by plasma related nonlinearities. After pioneering work of [1-2] only very small attention was devoted to HBTs. In this work, we present experimental studies of THz detection by different HBTs fabricated using InP double HBT (DHBT) technologies [3]. Different devices were investigated: single-finger devices and multi-finger devices formed using equally spaced parallel single-transistor fingers [4]. We have evaluated the room temperature detection performances of the devices in the sub-THz range from 250 GHz up to 650 GHz and analyse in details the physical mechanisms of THz detection. Finally, THz domain is an excellent non-contact probe of water content in biological tissues [5]. We also show that the sensitive HBTs detectors can be used for THz spectroscopy and 2D THz imaging to study the water dynamics of sorghum (a grass species cultivated for its grain) by monitoring the dehydration kinetics of its leaves.