Variable-wavelength frequency-domain terahertz ellipsometry.

We report an experimental setup for wavelength-tunable frequency-domain ellipsometric measurements in the terahertz spectral range from 0.2 to 1.5 THz employing a desktop-based backward wave oscillator source. The instrument allows for variable angles of incidence between 30 degrees and 90 degrees and operates in a polarizer-sample-rotating analyzer scheme. The backward wave oscillator source has a tunable base frequency of 107-177 GHz and is augmented with a set of Schottky diode frequency multipliers in order to extend the spectral range to 1.5 THz. We use an odd-bounce image rotation system in combination with a wire grid polarizer to prepare the input polarization state. A highly phosphorous-doped Si substrate serves as a first sample model system. We show that the ellipsometric data obtained with our novel terahertz ellipsometer can be well described within the classical Drude model, which at the same time is in perfect agreement with midinfrared ellipsometry data obtained from the same sample for comparison. The analysis of the terahertz ellipsometric data of a low phosphorous-doped n-type Si substrate demonstrates that ellipsometry in the terahertz spectral range allows the determination of free charge-carrier properties for electron concentrations as low as 8x10(14) cm(-3).

[1]  P Kuske,et al.  Brilliant, coherent far-infrared (THz) synchrotron radiation. , 2003, Physical review letters.

[2]  P. Drude.  Beobachtungen über die Reflexion des Lichtes am Antimonglanz , 1888 .

[3]  Tino Hofmann,et al.  Terahertz magneto-optic generalized ellipsometry using synchrotron and blackbody radiation , 2006 .

[4]  Eugene A. Irene,et al.  Handbook of Ellipsometry , 2005 .

[5]  Xicheng Zhang,et al.  Materials for terahertz science and technology , 2002, Nature materials.

[6]  Abul K. Azad,et al.  Experimental demonstration of frequency-agile terahertz metamaterials , 2008 .

[7]  R. Rosenfeld.  Nature , 2009, Otolaryngology--head and neck surgery : official journal of American Academy of Otolaryngology-Head and Neck Surgery.

[8]  P. Yeh,et al.  Optical Waves in Layered Media , 1988 .

[9]  M. Schubert.  Infrared ellipsometry on semiconductor layer structures , 2004 .

[10]  M. Kuwata-Gonokami,et al.  Terahertz time domain magneto-optical ellipsometry in reflection geometry , 2004 .

[11]  Masanori Hangyo,et al.  Measurement of complex optical constants of a highly doped Si wafer using terahertz ellipsometry , 2001 .

[12]  Masud Mansuripur,et al.  The Physical Principles of Magneto-optical Recording , 1995 .

[13]  Robert W. Collins,et al.  Automatic rotating element ellipsometers: Calibration, operation, and real‐time applications , 1990 .

[14]  Kirk Ct,et al.  Quantitative analysis of the effect of disorder-induced mode coupling on infrared absorption in silica. , 1988 .

[15]  G. Jellison,et al.  Two-modulator generalized ellipsometry: experiment and calibration. , 1997, Applied optics.

[16]  Dwight L. Woolard,et al.  Terahertz Frequency Sensing and Imaging: A Time of Reckoning Future Applications? , 2005, Proceedings of the IEEE.

[17]  Michael S. Shur,et al.  Terahertz sensing technology , 2009, GLSVLSI '09.

[18]  P. G. Snyder,et al.  Determination of AlAs optical constants by variable angle spectroscopic ellipsometry and a multisample analysis , 1995 .

[19]  Akhlesh Lakhtakia,et al.  Introduction to Complex Mediums for Optics and Electromagnetics , 2003 .

[20]  Craig M. Herzinger,et al.  Ellipsometric determination of optical constants for silicon and thermally grown silicon dioxide via a multi-sample, multi-wavelength, multi-angle investigation , 1998 .

[21]  Xiang Zhang,et al.  Negative refractive index in chiral metamaterials. , 2009, Physical review letters.

[22]  E. Korte,et al.  Infrared Spectroscopic Ellipsometry , 2006 .

[23]  R. Collins,et al.  Multichannel mueller matrix ellipsometry for simultaneous real-time measurement of bulk isotropic and surface anisotropic complex dielectric functions of semiconductors. , 2003, Physical review letters.

[24]  M. G. Clark.  Handbook on Semiconductors. Device Physics Vol 4 , 1982 .

[25]  M. Schubert.  Infrared Ellipsometry on Semiconductor Layer Structures: Phonons, Plasmons, and Polaritons , 2010 .

[26]  Gwyn P. Williams.  Filling the THz gap—high power sources and applications , 2006 .

[27]  Joseph S. Melinger,et al.  Guided-wave terahertz spectroscopy of molecular solids [Invited] , 2009 .

[28]  E. Palik.  Handbook of Optical Constants of Solids , 1997 .

[29]  Masayoshi Tonouchi,et al.  Cutting-edge terahertz technology , 2007 .

[30]  Takashi Fujii,et al.  Measurement of the Soft-Mode Dispersion in SrTiO3 by Terahertz Time-Domain Spectroscopic Ellipsometry , 2009 .

[31]  C. Brosseau.  Fundamentals of Polarized Light: A Statistical Optics Approach , 1998 .

[32]  Patrick Mounaix,et al.  Tunable terahertz metamaterials with negative permeability , 2009 .

[33]  D. Aspnes.  Precision bounds to ellipsometer systems. , 1975, Applied optics.

[34]  R. Temkin,et al.  Observation of frequency-locked coherent terahertz Smith-Purcell radiation. , 2005, Physical review letters.

[35]  D. Mittleman.  Sensing with terahertz radiation , 2003 .

[36]  R. Azzam,et al.  Ellipsometry and polarized light : North Holland, Amsterdam, 1987 (ISBN 0-444-87016-4). xvii + 539 pp. Price Dfl. 75.00. , 1987 .

[37]  Blaine D. Johs.  Regression calibration method for rotating element ellipsometers , 1993 .

[38]  T. S. Moss,et al.  Handbook on semiconductors , 1980 .

[39]  Ilsin An,et al.  Rotating-compensator multichannel ellipsometry: Applications for real time Stokes vector spectroscopy of thin film growth , 1998 .

[40]  Daniel R. Grischkowsky,et al.  Optical and electronic properties of doped silicon from 0.1 to 2 THz , 1990 .

[41]  Tino Hofmann,et al.  Conduction-band electron effective mass in Zn0.87Mn0.13Se measured by terahertz and far-infrared magnetooptic ellipsometry , 2006 .

[42]  M. Schubert,et al.  Hole diffusion profile in a p-p+ silicon homojunction determined by terahertz and midinfrared spectroscopic ellipsometry , 2009 .

[43]  E. Linfield,et al.  Terahertz semiconductor-heterostructure laser , 2002, Nature.

[44]  G. Jellison,et al.  Two-modulator generalized ellipsometry: theory. , 1997, Applied optics.