Advanced Terahertz Frequency-Domain Ellipsometry Instrumentation for In Situ and Ex Situ Applications

Philipp Kühne, Nerijus Armakavicius, Vallery Stanishev, Craig M. Herzinger, Mathias Schubert, Vanya Darakchieva

Research output: Contribution to journalArticlepeer-review

42 Scopus citations


We present a terahertz (THz) frequency-domain spectroscopic ellipsometer design that suppresses formation of standing waves by use of stealth technology approaches. The strategy to suppress standing waves consists of three elements geometry, coating, and modulation. The instrument is based on the rotating analyzer ellipsometer principle and can incorporate various sample compartments, such as a superconducting magnet, in situ gas cells, or resonant sample cavities, for example. A backward wave oscillator and three detectors are employed, which permit operation in the spectral range of 0.1-1 THz (3.3-33 cm-1 or 0.4-4 meV). The THz frequency-domain ellipsometer allows for standard and generalized ellipsometry at variable angles of incidence in both reflection and transmission configurations. The methods used to suppress standing waves and strategies for an accurate frequency calibration are presented. Experimental results from dielectric constant determination in anisotropic materials, and free charge carrier determination in optical Hall effect (OHE), resonant-cavity enhanced OHE, and in situ OHE experiments are discussed. Examples include silicon and sapphire optical constants, free charge carrier properties of two-dimensional electron gas in a group III nitride high electron mobility transistor structure, and ambient effects on free electron mobility and density in epitaxial graphene.

Original languageEnglish (US)
Pages (from-to)257-270
Number of pages14
JournalIEEE Transactions on Terahertz Science and Technology
Issue number3
StatePublished - May 2018


  • Cavity enhancement
  • dielectric functions
  • dielectrics
  • ellipsometry
  • free charge carrier properties
  • frequency domain
  • graphene
  • group III nitrides
  • high electron mobility transistor (HEMT)
  • optical Hall effect (OHE)
  • optical constants
  • spectroscopy
  • stealth technology
  • terahertz (THz)

ASJC Scopus subject areas

  • Radiation
  • Electrical and Electronic Engineering


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