Enhanced terahertz emission from strain-induced InGaAs/InAlAs superlattices (original) (raw)

Strain-induced InGaAs/InAlAs superlattices for terahertz radiation

arXiv: Materials Science, 2018

We study the influence of residual strain in InGaAs/InAlAs superlattice (SL) on the ultrafast photocarrier dynamics under femtosecond laser excitation. We propose and fabricate a novel-designed strained InGaAs/InAlAs SL which allows us to obtain an ultrashort photocarrier relaxation time of tausim\tau\simtausim 1.5 ps without Be-doping of the InGaAs photoconductor. We assume two dominant mechanisms to be responsible for a sharp reduction of tau\tautau: photocarriers trapping by defect levels in InAlAs barriers and increased photocarriers scattering at InGaAs/InAlAs interface roughness due to residual strain in the SL. The THz time-domain spectroscopic measurements reveal an increase in both emitted THz waveform and spectrum amplitudes with an increase of residual strain in SL. The results might be of considerable interest for accommodating the needs of THz pulsed spectroscopy and imaging in fundamental and applied branches of THz science and technology.

Propagation Effects of THz Waves in InAs-Based Heterostructures

Journal of Nanoscience and Nanotechnology, 2014

We have investigated THz radiation characteristics along different directions, either reflective or along lateral by using InAs-based heterostructures. Firstly, we demonstrate the phase shift with InAs layer thickness, revealing the change of dominant THz wave generation mechanism along both directions. Along the lateral direction, the time-domain signals in thin InAs epilayers showed an abrupt phase and amplitude change at certain time delays which suggest the interference between two rays at the photoconductive switch. This behavior was further substantiated by the multiple cavity modes in Fourier-transformed spectra and by the amplitude variation with excitation spot displacement.

Terahertz emission characteristics of ErAs:InGaAs-based photoconductive antennas excited at 1.55 μm

Applied Physics Letters, 2010

We characterize ErAs: In 0.53 Ga 0.47 As superlattices as substrates for photoconductive terahertz emitters excited at 1.55 m. The bandwidth of the emitted radiation is studied as a function of the superlattice period ͑or equivalently the electron lifetime͒ and the applied bias field. The results show that a variation in the electron lifetime from 0.2 to 6.3 ps does not considerably influence the bandwidth of the emitted radiation. However, the bandwidth increases linearly from 2.6 to 3.0 THz as the applied bias field is increased from 7 to 30 kV/cm. At higher bias fields, saturation is observed. The largest measured bandwidth is 3.1 THz.

Directional terahertz emission from corrugated InAs structures

Optics Express, 2013

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. As an important practical source of pulsed electromagnetic radiation at terahertz (THz) frequencies, the photo-excitation of semiconductor surfaces by femtosecond (fs) laser pulses has been widely used over the past two decades. A vast array of compound semiconductors have been examined with regard to their material parameters, including InAs, InSb, GaAs and InP. The THz radiation emitted from these materials has been attributed to either photo-carrier acceleration caused by band-bending near the semiconductor surface or to the large diffusion velocity difference between electrons and holes (the photo-Dember effect). These drift and diffusive transport mechanisms of the photo-excited carriers are identified separately from those of the different bulk compound semiconductors: In the case of GaAs, the THz radiation is known to be produced mainly by the surface electric field, 2 whereas the radiation from InAs is mainly governed by the photo-Dember effect. 3 Comparison studies were also performed on the THz radiation from GaAs and InAs, 4 while a detailed explanation of the THz radiation processes from InAs was provided in terms of drift and diffusion. Further technological advances have been made toward efficient radiation sources with higher output powers and/or tunability 7 and with better spatial resolution that is sometimes beyond the diffraction limit. 8 Recently, THz waves with increased amplitude and bandwidth have been reported in periodically metal-patterned In 0.53 Ga 0.47 As (and GaAs) by breaking lateral symmetry in their diffusion currents, 9,10 while the transfer of THz waves over long distances was demonstrated by using either a laser-plasma filament 11 or an optical fiber coupled with tilted InAs tips, while retaining superior spatial resolution. From the materials viewpoint, InAs is known to be one of the most intense sources among the various candidate semiconductors because it has an electron mobility (reaching up to 30,000 cm 2 /V•s) that is much higher than the hole mobility (∼240 cm 2 /V•s), leading to efficient photo-Dember current generation. Also, the 800

Excitation wavelength dependence of terahertz emission from semiconductor surface

Applied Physics Letters, 2006

The authors have measured terahertz radiation from InSb, InAs, and InGaAs excited by femtosecond optical pulses at wavelengths of 1560, 1050, and 780 nm. The amplitude of the terahertz field strongly depends on the pump wavelengths. Among the materials, the InSb emitter shows the largest terahertz emission amplitude at high power 1560 nm excitation, whereas 780 nm excitation provides the weakest. With increasing photon energy, the increase in emission amplitude from InAs is less as compared to that from InGaAs. The decrease from InSb and InAs originates in low mobilities of L or X valley carriers generated by intervalley scatterings.

Simulation and optimisation of terahertz emission from InGaAs and InP photoconductive switches

Solid State Communications, 2005

We simulate the terahertz emission from laterally biased InGaAs and InP using a three-dimensional carrier dynamics model in order to optimise the semiconductor material. Incident pump-pulse parameters of current Ti:Sapphire and Er:fibre lasers are chosen, and the simulation models the semiconductor's bandstructure using parabolic Γ, L and X valleys, and heavy holes. The emitted terahertz radiation is propagated within the semiconductor and into free space using a model based on the Drude–Lorentz dielectric function. As the InGaAs alloy approaches InAs an increase in the emitted power is observed, and this is attributed to a greater electron mobility. Additionally, low-temperature grown and ion-implanted InGaAs are modelled using a finite carrier trapping time. At sub-picosecond trapping times the terahertz bandwidth is found to increase significantly at the cost of a reduced emission power.

Terahertz emission from gradient InGaAs surfaces

Applied Physics Letters, 2021

We present an experimental study of the terahertz emission from In x Ga 1Àx As epitaxial layers that were grown while varying the alloy fraction x. We observe the terahertz emission that is significantly different depending on the variation direction of the alloy fraction. We attribute the difference to the significant change of the band bending induced in the growth direction and to the position-dependent variation of the effective mass.

Characterisation of InAs:GaAs quantum dot-based photoconductive THz antennas

2013 IEEE Photonics Conference, 2013

• Background, THz research and devices -Ultrafast semiconductors and photonics -The quantum-dot solution • QD photoconductive THz devices and test setups • Performance of QD-based THz sources -Pulsed operation, "traditional" Ti:Sapphire-driven -Characteristic output signals and efficiency -Long-wavelength options