Propagation Effects of THz Waves in InAs-Based Heterostructures (original) (raw)
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Nexus between directionality of terahertz waves and structural parameters in groove patterned InAs
Journal of Applied Physics, 2013
We performed terahertz (THz) time-domain spectroscopy in various geometries, for characterizing the directivity of THz waves emitted from groove patterned InAs structures. We first identified two transient transport processes as underlying THz emission mechanisms in InAs epilayers with different thicknesses. Carrier drift around the surface depletion region was predominant for the THz wave generation in the thin sample group (10-70 nm), whereas electronic diffusion overrode the drift currents in the thick sample group (370-900 nm) as revealed by the amplitude change and phase reversal. Through a combination of electron-beam lithography and inductively coupled plasma etching in 1 lm-thick InAs epilayers, we could further periodically fabricate either asymmetric V-groove patterns or symmetric parabolic apertures. The THz amplitude was enhanced, particularly along the line-of-sight transmissive direction when the periodic groove patterns act as microscale reflective mirrors separated by a scale of the diffusion length. V C 2013 American Institute of Physics. [http://dx.
Optical and Quantum Electronics, 2016
We present a fast and robust optical method of determining carrier concentrations in heavily doped layered structures. We discuss several advantages of the technique as compared to other, more commonly applied methods using as an example InAs based devices used for THz radiation generation. Our approach leads to a more accurate estimation of doping levels in the investigated structures and aids the standard Hall measurements in precise predictions of radiative efficacy in the THz region. Predicted enhancement factors reproduce THz-Time Domain Spectroscopy (TDS) experiment results within a 2 % accuracy. Keywords FDR Á Doping density Á Carrier concentration Á THz Á InAs This article is part of the Topical Collection on TERA-MIR: Materials, Generation, Detection and Applications.
Thickness dependence of terahertz emission in InAs and its application to transmissive source
2011
In situ study of the growth properties of Ni-rare earth silicides for interlayer and alloy systems on Si(100) J. Appl. Phys. 111, 043511 (2012) Surface diffusion and layer morphology of ((112)) GaN grown by metal-organic vapor phase epitaxy J. Appl. Phys. 111, 033526 Search for a small hole in a cavity wall by intermittent bulk and surface diffusion J. Chem. Phys. 136, 054115 Simultaneous step meandering and bunching instabilities controlled by Ehrlich-Schwoebel barrier and elastic interaction Appl. Phys. Lett. 99, 263106 (2011) Chemical bond modification in porous SiOCH films by H2 and H2/N2 plasmas investigated by in situ infrared reflection absorption spectroscopy Abstract. Terahertz(THz) radiation properties from InAs layers grown on GaAs has been studied as a function of thickness ranging from 0. ȝm to 1.74 ȝm. The amplitude showed a monotonic increment up to 0.9 ȝm, followed by a decrement at 1.74 ȝm. The phase-shift between 0.07 and 0.37 ȝm was also observed, which was possibly associated with the transition of the major generation mechanism from drift to diffusion with increasing thickness.
Directional terahertz emission from diffusion-engineered InAs structures
We have designed and fabricated a new type of terahertz (THz) emitter that radiates THz waves along the surface-normal direction because of the lateral distributions of the transient electric dipoles. The excitation and measurements were performed using a conventional THz time-domain spectroscopy scheme with femtosecond optical pulses. The corrugated mirror patterns on the InAs layers made the radiation directional along the surface-normal direction, and the emission efficiency was controlled by adjustment of the pattern width.
Applied Optics, 2005
InAs has previously been reported to be an efficient emitter of terahertz radiation at low excitation fluences by use of femtosecond laser pulses. The scaling and saturation of terahertz emission from a (100) InAs surface as a function of excitation fluence is measured and quantitatively compared with the emission from a GaAs large-aperture photoconductive switch. We find that, although the instantaneous peak radiated terahertz field from (100) InAs exceeds the peak radiated signals from a GaAs largeaperture photoconductive switch biased at 1.6 kV͞cm, the pulse duration is shorter. For the InAs source the total energy radiated is less than can be obtained from a GaAs large-aperture photoconductive switch.
Physical Review B, 2005
Polarized second-harmonic generation and terahertz radiation in reflection from (100), (110), and (111) faces of n -type InAs crystals are investigated as a function of the sample azimuthal orientation under excitation from femtosecond Ti:sapphire laser pulses. The expressions describing the second-order response (optical second-harmonic generation and optical rectification) in reflection from zinc-blende crystals, such as InAs, are calculated taking into account the bulk electric-dipole contribution and the first-order surface electric-field-induced contribution. It is shown that the two contributions can be separated based on rotation symmetry considerations. Moreover, a direct comparison of the second-harmonic generation and terahertz radiation emission indicates that the observed dominant surface electric-field-induced optical rectification component may be attributed to the large free-carrier contribution to the third-order susceptibility in InAs.
Enhanced terahertz emission from strain-induced InGaAs/InAlAs superlattices
Journal of Applied Physics, 2019
We propose, fabricate, and evaluate strain-induced InGaAs/InAlAs superlattice (SL), which can efficiently radiate broadband terahertz (THz) waves. By means of optical pump-probe measurements, we demonstrate ultrashort photocarriers relaxation times of τ 1:7 ps without Be-doping of InGaAs photoconductive layers. We assume two dominant mechanisms to be responsible for a sharp reduction of τ in strained SL, which are photocarriers scattering at InGaAs/InAlAs heterointerface roughness and the decrease in the energy bandgap of InGaAs photoconductive layers due to the residual strain. The THz time-domain spectroscopic measurements reveal the rise in both emitted THz waveform and spectrum amplitudes with an increase of the residual strain in SL, in particular, at the low-frequency region. We refer this to the band structure engineering due to the residual strain in SL-since InGaAs photoconductive layers become compressively strained, this reduces the semiconductor's energy bandgap, thus more photocarriers can contribute to the THz emission. The results might be of specific interest for the development of portable THz pulsed spectroscopic and imaging systems and other fundamental and applied aspects of the THz science and technology.