Journal
REVIEW OF SCIENTIFIC INSTRUMENTS
Volume 81, Issue 2, Pages -Publisher
AMER INST PHYSICS
DOI: 10.1063/1.3297902
Keywords
backward wave oscillators; ellipsometry; optical polarisers; phosphorus; silicon
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Funding
- Army Research Office [W911NF-09-C-0097]
- National Science Foundation [0922937, 0907475]
- NSF MRSEC QSPIN at UNL [DMR-0820521]
- Division Of Materials Research
- Direct For Mathematical & Physical Scien [0907475] Funding Source: National Science Foundation
- Division Of Materials Research
- Direct For Mathematical & Physical Scien [0922937] Funding Source: National Science Foundation
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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).
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