Guided-wave THz time-domain spectroscopy of highly doped silicon using parallel-plate waveguides

R. Mendis
2006 Electronics Letters  
A novel spectroscopy technique that uses parallel-plate waveguides for the characterisation of highly conductive materials in the terahertz (THz) frequency regime is presented. This guided-wave technique resolves some of the fundamental problems associated with standard THz time-domain spectroscopy (THz-TDS) as applied to these optically dense materials. The technique is demonstrated by measuring the conductivity of highly phosphorus doped silicon. Introduction: Ever since undistorted
more » ... ond terahertz (THz) pulse propagation was demonstrated using parallel-plate metal waveguides [1, 2] there has been considerable interest in these waveguiding structures for THz applications. These parallel-plate structures have been used to demonstrate two-dimensional interconnect layers [3], sense nanometre water layers [4], study photonic crystals [5] , and for building biosensing systems [6] . This Letter describes another novel use of these structures for the characterisation of highly conductive, optically dense materials resolving some of the fundamental problems associated with standard THz time-domain spectroscopy (THz-TDS) [7, 8] . THz-TDS is generally carried out in two configurations, one where the THz beam is transmitted through the sample [7] , the other where the beam is reflected off of the sample [8] . The transmission method is not effective for highly conductive materials, as the sample thickness has to be reduced to impractical limits to obtain a measurable signal. In this case, the reflection method is preferred, provided it is possible to discriminate the sample signal from the reference signal. If this is not possible, this would also breakdown. Furthermore, obtaining precise sample and reference positioning for the reflection method is also quite challenging [8] . The guided-wave spectroscopy technique presented here overcomes these problems, and would be ideal for materials such as highly doped semiconductors, superconductors, and conducting polymers. To demonstrate the technique, highly phosphorus-doped silicon (Si) with a carrier density >10 18 cm À3 is used as the candidate material.
doi:10.1049/el:20063418 fatcat:rn4vd7sayfdspkiaurl42krtwe