Field Effect Transistors for Terahertz Detection

For optical frequencies, there are systems known from the prior art which not only make it possible to represent an object two-dimensionally, but also detect it three-dimensionally, in other words to determine the distance between the object and the detector for individual pixels. In contrast, the object of the present invention is to provide a system and a method for detecting an object three-dimensionally using high-frequency electromagnetic radiation at a frequency in a range of 100 GHz to 10 THz. According to the invention, this object is met by a system for detecting an object three-dimensionally using high-frequency electromagnetic radiation, the system comprising a radiation source for radiating high frequency radiation at a frequency in a range of 100 GHz to 10 THz, a receiver for detecting the high frequency radiation emitted from the radiation source, said receiver comprising an antenna element and a field effect transistor for mixing the high frequency radiation emitted by the radiation source with a local oscillator signal, wherein the field effect transistor comprises a source, a drain and a gate, and comprising a signal source for generating an electric modulation signal, wherein the signal source is connected to the radiation source in such a way that the high frequency radiation can be modulated by the modulation signal, and wherein the signal source is connected to the gate of the field effect transistor in such a way that the sensitivity of the field effect transistor can be modulated using a local oscillator signal coupled at a fixed phase to the modulation signal.

Experiments on terahertz radiation detection with InGaAs/InAlAs field-effect transistor in quantizing magnetic field are reported. We observed oscillations of the photovoltaic signal analogous to the Shubnikov–de Haas oscillations, as well as their strong enhancement at the cyclotron resonance conditions. The results are described quantitatively within the frame of a theory which takes into account a new source of nonlinearity related to the Landau quantization of the conduction band.

We present a Terahertz (THz) p-Ge laser operating in a cyclotron resonance (CR) mode. Thanks to the use of the optimum crystallographic orientation of p-Ge with respect to crossed E(perpendicular to)B fields, the laser line frequency is continuously tunable in the range 1.2-2.8 THz (40-90 cm(-1)) with the linewidth being 6 GHz (0.2 cm(-1)). We also show that due to such a wide CR radiation range, the laser can serve as a base for a THz spectrometer.

Imaging at 0.6 THz is tested with a commercial GaAs high-electron-mobility transistor (HEMT) operated at room temperature. The results allow the assessment of the potential of future antenna-fitted HEMT arrays for real-time imaging.

The channel of a field effect transistor can act as a resonator for plasma waves propagating in a two-dimensional electron gas. The plasma frequency increases with reduction of the channel length and can reach the terahertz (THz) range for nanometer size transistors. Recent experimental results show these transistors can be potential candidates for a new class of THz detectors and emitters. This work gives an overview of our recent relevant experimental results. We also outline unresolved problems and questions concerning THz detection and emission by nanometer transistors.