Optical and electronic properties of doped silicon from 0.1 to 2 THz
TL;DR: Using a source of freely propagating subpicosecond pulses of THz radiation, this article measured the absorption and dispersion of both N and P-type, 1 Ω cm silicon from 0.1 to 2 THz.
Abstract: Using a source of freely propagating subpicosecond pulses of THz radiation, we have measured the absorption and dispersion of both N‐ and P‐type, 1 Ω cm silicon from 0.1 to 2 THz. These results give the corresponding frequency‐dependent complex conductance over the widest frequency range to date. The data provide a complete view on the dynamics of both electrons and holes and are well fit by the simple Drude relationship.
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IBM1
TL;DR: In this paper, the authors measured the far-infrared absorption and dispersion from 0.2 to 2 THz of the crystalline dielectrics sapphire and quartz, fused silica, and the semiconductors silicon, gallium arsenide, and germanium.
Abstract: Using the method of time-domain spectroscopy, we measure the far-infrared absorption and dispersion from 0.2 to 2 THz of the crystalline dielectrics sapphire and quartz, fused silica, and the semiconductors silicon, gallium arsenide, and germanium. For sapphire and quartz, the measured absorptions are consistent with the earlier work below 0.5 THz. Above 1 THz we measure significantly more absorption for sapphire, while for quartz our values are in reasonable agreement with those of the previous work. Our results on high-purity fused silica are consistent with those on the most transparent fused silica measured to date. For the semiconductors, we show that many of the previous measurements on silicon were dominated by the effects of carriers due to impurities. For high-resistivity, 10-kΩ cm silicon, we measure a remarkable transparency together with an exceptionally nondispersive index of refraction. For GaAs our measurements extend the precision of the previous work, and we resolve two weak absorption features at 0.4 and 0.7 THz. Our measurements on germanium demonstrate the dominant role of intrinsic carriers; the measured absorption and dispersion are well fitted by the simple Drude theory.
2,084 citations
TL;DR: A comprehensive review of the various techniques used for terahertz image formation can be found in this paper, as well as numerous examples which illustrate the many exciting potential uses for these emerging technologies.
Abstract: Within the last several years, the field of terahertz science and technology has changed dramatically. Many new advances in the technology for generation, manipulation, and detection of terahertz radiation have revolutionized the field. Much of this interest has been inspired by the promise of valuable new applications for terahertz imaging and sensing. Among a long list of proposed uses, one finds compelling needs such as security screening and quality control, as well as whimsical notions such as counting the almonds in a bar of chocolate. This list has grown in parallel with the development of new technologies and new paradigms for imaging and sensing. Many of these proposed applications exploit the unique capabilities of terahertz radiation to penetrate common packaging materials and provide spectroscopic information about the materials within. Several of the techniques used for terahertz imaging have been borrowed from other, more well established fields such as x-ray computed tomography and synthetic aperture radar. Others have been developed exclusively for the terahertz field, and have no analogies in other portions of the spectrum. This review provides a comprehensive description of the various techniques which have been employed for terahertz image formation, as well as discussing numerous examples which illustrate the many exciting potential uses for these emerging technologies.
962 citations
TL;DR: In this article, a novel method for fast and reliable extraction of material parameters in terahertz time-domain spectroscopy was proposed, which could be applied for most materials and requires neither simplifying assumptions nor samples of different thickness for the extraction.
Abstract: This paper introduces a novel method that allows fast and reliable extraction of material parameters in terahertz time-domain spectroscopy. This method could be applied for most materials and requires neither simplifying assumptions nor samples of different thickness for the extraction. The presented extraction procedure operates either on truncated terahertz signals when temporal windowing is possible, or on full ones otherwise. Some experimental examples covering all practical cases are given. In particular, the extraction procedure treats the tedious case of samples for which internal reflections of the terahertz pulse slightly overlap.
821 citations
Cites background from "Optical and electronic properties o..."
...Using ultrashort electromagnetic pulses, terahertz spectroscopy gives access to the complex refractive index of a wide variety of materials, such as dielectrics [1], semiconductors [2], liquids [3], and superconductors [4]....
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TL;DR: This method could be applied to any material with moderate absorption and requires only two measurements of the temporal profile of the terahertz pulses: a reference one without the sample and one transmitted through the sample.
Abstract: Time-domain spectroscopy allows fast and broadband measurement of the optical constants of materials in the terahertz domain. We present a method that improves the determination of the optical constants through simultaneous determination of the sample thickness. This method could be applied to any material with moderate absorption and requires only two measurements of the temporal profile of the terahertz pulses: a reference one without the sample and one transmitted through the sample.
462 citations
TL;DR: Fits using the Drude-Smith model show that films have the highest mobility, followed by nanowires and then nanoparticles, and that annealing the ZnO increases its mobility, and implications for electron transport in dye-sensitized solar cells are discussed.
Abstract: The terahertz absorption coefficient, index of refraction, and conductivity of nanostructured ZnO have been determined using time-resolved terahertz spectroscopy, a noncontact optical probe. ZnO properties were measured directly for thin films and were extracted from measurements of nanowire arrays and mesoporous nanoparticle films by applying Bruggeman effective medium theory to the composite samples. Annealing significantly reduces the intrinsic carrier concentration in the ZnO films and nanowires, which were grown by chemical bath deposition. The complex-valued, frequency-dependent photoconductivities for all morphologies were found to be similar at short pump-probe delay times. Fits using the Drude-Smith model show that films have the highest mobility, followed by nanowires and then nanoparticles, and that annealing the ZnO increases its mobility. Time constants for decay of photoinjected electron density in films are twice as long as those in nanowires and more than 5 times those for nanoparticles due to increased electron interaction with interfaces and grain boundaries in the smaller-grained materials. Implications for electron transport in dye-sensitized solar cells are discussed.
374 citations
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TL;DR: In this article, the present knowledge of charge transport properties in silicon, with special emphasis on their application in the design of solid-state devices, is reviewed, and most attention is devoted to experimental findings in the temperature range around 300 K and to high-field properties.
Abstract: This paper reviews the present knowledge of charge transport properties in silicon, with special emphasis on their application in the design of solid-state devices. Therefore, most attention is devoted to experimental findings in the temperature range around 300 K and to high-field properties. Phenomenological expressions are given, when possible, for the most important transport quantities as functions of temperature, field or impurity concentration. The discussion is limited to bulk properties, with only a few comments on surface transport.
1,067 citations
IBM1
TL;DR: By analyzing the propagation of terahertz electromagnetic pulses through water vapor, this work has made what it is believed are the most accurate measurements to date of the absorption cross sections of the water molecule for the nine strongest lines.
Abstract: We describe the application of a new high-brightness, terahertz-beam system to time-domain spectroscopy. By analyzing the propagation of terahertz electromagnetic pulses through water vapor, we have made what we believe are the most accurate measurements to date of the absorption cross sections of the water molecule for the nine strongest lines in the frequency range from 0.2 to 1.45 THz.
830 citations
TL;DR: In this article, the effect of free carriers on the optical constants has been determined by using reflectivity and absorption measurements in the region 5 to 35 micron, and the significance of ${m}_{s}$ is considered for four different types of energy band structure.
Abstract: By using reflectivity and absorption measurements in the region 5 to 35 micron, the effect of free carriers on the optical constants has been determined for $n$- and $p$-type germanium, silicon, and indium antimonide, and for $n$-type indium arsenide. The contribution of the free carriers to the electric susceptibility is obtained from the optical constants. A carrier effective mass, ${m}_{s}$, is defined in terms of the susceptibility, and the significance of ${m}_{s}$ is considered for four different types of energy band structure. The experimental values of ${m}_{s}$ are compared with those calculated by using data from other experiments. Good agreement was found for $n$- and $p$-type silicon, $n$-type germanium, and $p$-type indium antimonide. In $p$-type germanium, the susceptibility due to transitions between the overlapping bands in the valence band was taken into account. However, the resulting ${m}_{s}$, for a sample of \ensuremath{\sim}${10}^{19}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ impurity concentration, is larger by a factor of 1.8 than that calculated by using cyclotron resonance data. In $n$-type indium antimonide ${m}_{s}$ increases with carrier concentration. If one assumes ${m}_{s}$ to be energy-dependent, the shape of the conduction band calculated is consistent with previously reported measurements of the shift of the intrinsic absorption edge with electron concentrations. In the case of $n$-type indium arsenide, ${m}_{s}$ differs from the effective mass reported from thermoelectric measurements but gives good agreement with the values determined from the shift of the intrinsic absorption edge for an impure specimen.
590 citations
TL;DR: The far infrared optical constants of four crystalline materials at room temperature and at 1.5 K are reported and the first two are birefringent (uniaxial) and both sets the range from 30cm(-1) to 350 cm(-1).
Abstract: The far infrared optical constants of four crystalline materials at room temperature and at 1.5 K are reported. The materials are crystal quartz, sapphire, germanium, and silicon. The first two of these are birefringent (uniaxial) and both sets of optical constants are reported. The measurements extend over the range from 30 cm−1 to 350 cm−1.
308 citations