Plasmonic enhancement of sensitivity in terahertz (THz) photo-conductive detectors

We demonstrate enhancement of sensitivity in terahertz photoconductive detectors achieved by incorporation of plasmonic structures into the photo-conductive region of the detector. Auston switches based on lowtemperature grown GaAs (LT GaAs) have been reliably used for detection of THz pulses over two decades. This material exhibits high electron mobility with sub-picosecond carrier lifetimes and high dark resistivity. This combination is difficult to achieve in other materials. Application of LT GaAs in THz devices is nevertheless limited due to absorption characteristics of this material. Plasmonic structures can be employed to modify the distribution of the optical field in the photoconductive region and hence modify the response of the THz photoconductive detectors. We will discuss design of plasmonic structures to enhance the response of THz detectors based on LT GaAs and demonstrate incorporation of such structures into THz detectors. We also apply the developed design in integrated photo-conductive probes for THz near-field microscopy, where the enhancement of the material absorption translates into an increase of the detector sensitivity and an improvement in spatial resolution. Performance on these near-field probes that provide a spatial resolution of 3- 5 micrometers (∼1/100 of the wavelength) will be discussed and demonstrated.