Strong terahertz emission from (100) p-type InAs
This article was originally published as: Mendis, R, Smith, ML, Bignell, LJ, Vickers, REM & Lewis, RA, Strong terahertz emission from (100) p-type InAs, Journal of Applied Physics, December 2005, 98, 126104. Copyright American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics
Terahertz emission has been observed from (100) Zn-acceptor-doped InAs under illumination by fs pulses of... more Terahertz emission has been observed from (100) Zn-acceptor-doped InAs under illumination by fs pulses of near-infrared radiation. Turning the crystal about the surface normal produces two maxima per rotation, whether the angle of incidence is 45° or 75°, in contrast to (111) p-InAs, where three maxima per rotation have been reported. The emitted terahertz power has a quadratic variation with the pump power and decreases with increasing temperature in the range 20–300 K. This behavior is consistent with a photocurrent surge being the dominant terahertz generating mechanism at low excitation fluences. The p-type InAs generates about two orders of magnitude more power than the standard unbiased terahertz emitter, 1mm thick ZnTe.
New modes of THz generation by low-temperature-grown GaAsSb
© 2009, Elsevier Ltd.
The low-temperature growth of GaAs1−ySby with y = 0.4 and 0.85 has been reported recently along with characterization... more The low-temperature growth of GaAs1−ySby with y = 0.4 and 0.85 has been reported recently along with characterization by X-ray diffraction, Hall, and current–voltage measurements. Here we extend the characterization by employing reflectance spectroscopy in the range 5–18 THz to confirm the compositions of the grown layers. In the course of this work we established for the first time that GaAs1−ySby may serve as an emitter of THz radiation under optical excitation by ultrashort pulses of near-infrared radiation in two distinct experimental arrangements: THz is generated when an electrical bias is applied through a simple electrode structure, attributed to a photoconductive effect; and THz is generated by the pristine layers themselves, attributed to a surface-field effect. In each case the THz emission is compared directly with that from low-temperature-grown GaAs. The results presented here are for as-grown material. Suitable annealing may improve the THz emission even further.
Reflectance studies of candidate THz emitters
© 2009, Springer. The original publication is available at www.springerlink.com
Semiconductors are efficient emitters of terahertz (THz, 1012 Hz) radiation. Non-contact means of accurately measuring... more Semiconductors are efficient emitters of terahertz (THz, 1012 Hz) radiation. Non-contact means of accurately measuring the physical parameters of these materials are of great value. The reflectance of polar crystals yields important information. A dramatic change in reflectance occurs in the frequency range between the transverse-optical (TO) and the longitudinal-optical (LO) phonons. For many materials these frequencies are of the order of a few THz. Analysis of the reflectance in and near this region yields (a) the TO phonon frequency ω T , (b) the LO phonon frequency ω L , (c) the low-frequency or DC reflectance R(0), and thence the DC refractive index, n(0), and dielectric constant, ɛ(0); (d) the high-frequency or optical reflectance R(∞), and thence n(∞) and ɛ(∞) and (e) the phonon damping factor Γ. These constants depend on the lattice itself and may be described within the Lorentz model. If, in addition, the crystal possesses free carriers, reflectance measurements further yield (f) the plasma frequency ω P , and thence the carrier concentration n e/h and (g) the plasma damping factor γ which may be understood in terms of the Drude model. Samples in the form of a parallel plate give rise to interference fringes that yield (h) the sample thickness t. We have examined many polar crystals with a view to understanding THz emission from them with the overall goal of improving the emission efficiency. Measurements have been made in the region 1.5–21 THz (50–700 cm−1) of single and multilayer samples. We use the sum rule to check the internal consistency of the experimental measurements. We have re-examined the relationship between the phonon frequencies and the reduced ion mass. We find the effective spring constant is very similar in all I–VII materials studied and likewise within the II–VI and III–V classes. We use shell theory to account for these results.
Investigation of p-GaAsSb as a THz Emitter
©2008 The Electrochemical Society
Our purpose was to determine if GaAsSb might be made to emit THz-frequency electromagnetic radiation. Our result is... more Our purpose was to determine if GaAsSb might be made to emit THz-frequency electromagnetic radiation. Our result is that, with a suitable electric field imposed and under illumination by ultrashort pulses of near-infrared radiation, GaAsSb indeed emits THz radiation. To the best of our knowledge this is the first report of high-temperature-grown GaAsSb acting as a THz source. THz emission has been observed both by incoherent (pneumatic Golay cell) and by coherent (time-domain spectroscopy using electro-optic detection) experimental configurations. Both simple Ag paint and photolithographically formed Au on Ti antenna structures have been found to produce THz radiation. We compare our results with those from the better-known THz emitter, GaAs. In the case of GaAs, THz radiation is emitted even in the absence of applied bias. This is not the case for GaAsSb. We conclude that the photoconductive mechanism dominates in the emission of THz radiation from epitaxial single-crystal GaAsSb. A further proposal is made that such materials can be used with nanostructured surfaces for special THz-emission characteristics.
Terahertz imaging through self-mixing in a quantum cascade laser
P. Dean, Y.-L. Lim, A. Valavanis, R. Kliese, M. Nikolić, S. P. Khanna, M. Lachab, D. Indjin, Z. Ikonić, P. Harrison, A. D. Rakić, E. H. Linfield, and A. G. Davies; Opt. Lett. 36(13), p. 2587-2589 (2011) doi:10.1364/OL.36.002587
We demonstrate terahertz (THz) frequency imaging through use of a single quantum cascade laser (QCL) device for both... more We demonstrate terahertz (THz) frequency imaging through use of a single quantum cascade laser (QCL) device for both generation and sensing of THz radiation. Detection is achieved by utilising the effect of self-mixing in the QCL, and specifically by monitoring perturbations to the voltage across the QCL induced by light reflected from an external object back into the laser cavity. Self-mixing imaging offers high sensitivity, a potentially fast response, and a simple, compact optical design, and we show that it can be used to obtain high-resolution reflection images of exemplar structures. © 2010 Optical Society of America
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