Plasmonic GaN Detectors and Emitters for THz Frequencies
Fig. 1: GaN HEMT with antenna structure
Fig. 2: Detector sensitivity (noise-equivalent power) against gate bias for different transistor gate widths
Electronic device operation beyond the commonly known cut-off frequencies has been demonstrated employing plasmonic effects. As is known for some years now, charge transport in electronic semiconductor devices may show plasma waves within the channel of field-effect transistors, which become apparent at terahertz (THz) frequencies. These effects can be used to detect THz signals using conventional CMOS or III-V transistors, which is well documented in the recent literature. Some publications report THz emission due to plasmonic effects as well. The topic is of great interest since it opens up possibilities to operate devices based on the existing semiconductor components in the THz frequency range. GaN high-electron mobility transistors (GaN HEMTs) have shown particular potential in this regard, due to the high mobility and the advanced breakdown features. The THz range offers applications particularly in biology, medicine and industry because most materials have a characteristic spectral fingerprint at these frequencies.
In cooperation with the Goethe-Universität Frankfurt, FBH has started several activities in this field, targeting both the emitter and the detector side. The emission characteristics are investigated in the framework of a DFG project. Here, the focus is on establishing a well-defined high-frequency environment suppressing parasitics and thus allowing reproducible experiments on emission, which are essential for further clarification of the emission processes.
In 2014, an additional project on THz detection has been started funded by the Leibniz Association. Work is based on the FBH GaN MMIC process, which allows both to tailor the transistor structures to the specific needs and to realize THz antenna structures incorporating theses devices. Fig. 1 illustrates a bow-tie antenna with a GaN HEMT integrated in its center. First results (see Fig. 2) show GaN detectors with encouraging sensitivity values beyond those obtained with CMOS for similar geometries (see publication below).
Publication:
M. Bauer, A. Lisauskas, S. Boppel, M. Mundt, V. Krozer, H.G. Roskos, S. Chevtchenko, J. Würfl, W. Heinrich, G. Tränkle, "Bow-Tie-Antenna-Coupled Terahertz Detectors using AlGaN/GaN Field-Effect Transistors with 0.25 Micrometer Gate Length", Proc. 8th European Microwave Integrated Circuits Conf. (EuMIC 2013), Nürnberg, Germany, Oct. 6-8, pp. 212-215 (2013).
FBH research: 16.01.2014