I. Introduction
The THz spectrum of electromagnetic waves is non-ionizing and has a broad application area [1]. In [2] Dyakonov and Shur predicted that the instability of electron plasma waves in short channel FETs could be used as terahertz frequency radiation detector. Several THz imaging systems and different sensor technologies appeared, among others silicon based field effect transistors [2]–[5]. It found that not only high mobility devices, but silicon based detectors with integrated planar antennas could serve as fast imagers as well [8], [9], [14]–[21]. For such detectors a different, more phenomenological, description is given as well in [15] based on resistive self-mixing. The silicon or SiGe based sensor technologies offer an advantage over other material based solutions, like bolometers [22]–[24], the on-chip integration of read-out and signal processing circuitry [14]. Related to field effect transistor (FET) detectors, we can distinguish two basic operation modes: open drain and non zero drain current cases. The former provides higher sensitivity, while the later significantly higher response [6], though with dominant flicker noise. In [4], [11] homodyne and heterodyne mixing FET detectors are presented with outstanding performance, similar to that Schottky diodes offer. These results suggest that further improvements are still expected from silicon based sensors.