Novel photmixers with one-dimensional and two-dimensional nanocontacts for terahertz generation

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New developments of THz components and systems in recent years offer attractive opportunities for new security applications such as imaging measurements of hidden objects, spectroscopy of hazardous substances and tap-proof communication in wireless broadband systems. However, it is still necessary to obtain stable and high performance continuous-wave sources for frequencies up to several THz, which will allow very simple system architectures. The conventional technologies have significant limitations with respect to the achievable THz output power and frequencies. The proposed research project builds on innovative 1D or 2D nano-contacts with reliable high photocurrents > 3 mA and small device capacitance < 0.5 fF. Thus, much higher THz output power > 100 µW can be achieved at frequencies < 2 THz to perform imaging measurements even from remote objects and covers highest THz frequencies > 5 THz, which can easily identify the spectral absorption lines of different hazardous substances. Additionally, a quality study of materials and foods is possible. The high THz output power and the high signal-to-noise ratio will allow much faster measurements than with conventional photomixers. At the beginning, commer-cial nanowires (e.g. silver wires) and multilayer graphene sheets will be investigated for their suitability as a contact electrode on LT-GaAs. The adhesion and the reliable power density will be determined. On the basis of these results, first lateral and vertical THz photomixers will be designed and manufactured as well as measured and modeled initially up to 2 THz. The resulting equivalent circuit of the photomixer allows the optimization of selected antenna concepts to use in compact THz sources. The nano-contacted photomixer also opens the possibility to reduce the active photomixer area while maintaining high photocurrents and THz output power to integrate antenna concepts for > 2 THz. Together with the smaller capacitance high frequencies > 5 THz with high signal-to-noise ratio can be achieved. The realistic potential analysis with regard to the THz output power, the cut-off frequency and the reliability of the new photomixer will be carried out at an 800 nm system. This technology can also be applied easily to an 800 nm system with cheap and compact vertical-cavity surface-emitting lasers (VCSELs) and to a 1.55 µm system with telecom lasers to greatly simplify the system architecture.