We report measurements of acoustic phonon emission from a weakly coupled AlAs/GaAs superlattice (SL) under vertical electron transport. The phonons were detected using superconducting bolometers. A peak (resonance) was observed in parallel to the SL growth axis when electrical energy drop per period matched first mini-Brillouin zone-center mode. This mirrored by an increase differential conductance SL. These results are evidence for stimulated terahertz as previously predicted theoretically...

We present measurements of the electron Hall mobility in n-type GaAs1−xBix epilayers. observed no significant degradation with Bi incorporation GaAs, up to a concentration 1.2%. At higher (≥1.6%) some was observed, although there is apparent trend. Temperature dependent suggest neutral impurity scattering be dominant mechanism.

We studied the effect of Bi incorporation on hole mobility in dilute bismide alloy GaAs${}_{1\ensuremath{-}x}$Bi${}_{x}$ using electrical transport (Hall) and photoluminescence (PL) techniques. Our measurements show that decreases with increasing concentration. Analysis temperature-dependent Hall data $p$-type GaAsBi epilayers along low-temperature PL $p$-doped undoped suggests results formation several trap levels above valence band, which we attribute to Bi-Bi pair states. The decrease...

Spiral and pyramidal WS₂ domains controllably synthesized through chemical vapour deposition technique exhibit interesting optical properties.

Abstract Elemental two-dimensional (2D) crystals have recently emerged as promising materials for advanced electronics and optoelectronics applications. However, it remains challenging to achieve controllable growth of high-quality, ultra-thin flakes elemental 2D materials. Here, we demonstrate, the first time, a seed-assisted chemical vapor transport triangular highly crystalline trigonal selenium ( t -Se) oriented in (0001) direction, with lateral size >30 µ m. The polarization...

We present helicity resolved photoluminescence (PL) measurements of WS2 spiral (SPI) nanostructures. show that very high degree circular polarization (DCP) (~94 ± 4%) is obtained from multilayer SPI samples at room temperature upon excitation with a circularly polarized laser wavelength near-resonant the A-exciton (633 nm). TEM analysis showed these nanostructures have AB stacking in which inversion symmetry broken, and hence this leads to DCP. Comparison PL monolayer bi-layer samples, along...

We report temperature-dependent hot carrier dynamics in liquid-phase epitaxy-grown GaSb1−xBix epilayers with dilute amounts of Bi (x ≾ 0.4%). Degenerate pump–probe (λ = 800 nm) transient reflectivity (PPTR) was used to investigate the epilayers. The PPTR signal consists two processes (fast and slow) at all temperatures for fast, relaxation time, which is attributed combined effect intervalley scattering thermalization carriers below cryogenic (<100 K), observed increase an temperature...

We have generated pulsed beams of $\ensuremath{\sim}\mathrm{THz}$ monochromatic longitudinal acoustic phonons by ultrafast laser excitation GaAs/AlAs superlattices. The propagated ballistically across the GaAs substrates at low temperatures and were detected using superconducting aluminum bolometers. Between generator superlattice bolometer was a second structure which acted as reflective band-stop filter. made measurements phonon pulses in various samples for filter stop band either tune or...

Magnetic field and temperature dependent resistivity measurements on n-type GaAs1-xBix epitaxially grown films show clear Shubnikov de Haas oscillations in the range 0 ≤ x 0.0088. An overall decrease electron effective mass is observed for this of compositions. Accounting known giant bandgap bowing spin orbit bowing, measured changes are qualitative agreement with perturbation theory applied to these energy band changes, confirming that bismuth mainly perturbs valence band. The stronger...

We have used femtosecond pump-probe techniques to generate and detect coherent transverse quasitransverse polarized acoustic phonons in GaAs∕AlAs superlattices. Direct generation of is achieved using superlattices grown on the low-symmetry, (311) (211), crystal planes. The frequency generated determined by superlattice period region 0.4THz. dependence mode structure pump polarization suggests that a Raman scattering process responsible for phonon generation. Using bolometers back surface...

It has been theoretically predicted that isolated Bi forms a resonant state in the valence band of dilute bismide alloy, ${\mathrm{GaAs}}_{1\ensuremath{-}x}{\mathrm{Bi}}_{x}$. We present ultrafast pump-probe reflectivity measurements this interesting alloy system, which provide experimental evidence for state. The transients pump/probe wavelengths \ensuremath{\lambda} \ensuremath{\sim} 860--900 nm have negative amplitude, we attribute to absorption probe pulse by pump induced carriers are...

Abstract Dilute III–V alloys containing N or Bi share many features that are common, but some distinct. In GaP and GaAs, both the substituent species behave as isoelectronic impurity traps lead to a giant bandgap bowing phenomenon. The isolated impurities generate bound states in resonant GaAs. pairs have been observed GaAs whereas not nor Low temperature photoluminescence studies on 1– x show undulations spectra these associated with Bi–Bi pairs. Theoretical arguments for differing...

This paper presents design of a high gain conventional bow-tie photoconductive antenna in the THz frequency band. Simulation results proposed are presented this paper. The also deals with effect silicon lens on radiation pattern which enhances directivity by considerable amount.

Abstract Terahertz time-domain spectroscopy (THz-TDS) provides a non-contact, non-destructive method for evaluating different materials and their properties. This short review discusses the commonly used numerical models estimation of thickness, refractive index, surface interface roughness paints, thermal barrier coatings, polymer coatings using THz-TDS in reflection geometry. To demonstrate applicability these models, we paint layers on metallic substrates extracted paraments by fitting...

The authors report time resolved measurements and control of photoinduced spin carrier relaxations in InMnSb ferromagnetic films with 2% Mn content (grown by low-temperature molecular beam epitaxy) using femtosecond laser pulses, compare them to analogous on InBeSb InSb films. In this work, magneto-optical Kerr effect standard pump-probe techniques provided a direct measure the photoexcited lifetimes, respectively. They observe decrease times high fluence regime an absence temperature...

We report time resolved measurements of spin and carrier relaxation in InAs films with densities 1.3×1016 1.6×1016cm−3 grown on (001) (111) GaAs, respectively. used standard pump-probe magneto-optical Kerr effect spectroscopy at different excitation wavelengths, power densities, temperatures. observed sensitivity to the photoinduced density but not variation temperature. explain our results using Elliot–Yafet picture process narrow gap semiconductors.

We present a Raman spectroscopic study of GaAs1−xBix epilayers grown by molecular beam epitaxy. have investigated the anharmonic effect on GaAs-like longitudinal optical phonon mode (LOGaAs′) for different Bi concentrations at various temperatures. The results are analyzed in terms damping induced thermal and compositional disorder. observed that anharmonicity increases with concentration as evident from increase constants. In addition, lifetime decreases increasing GaAs1−xBix.

We present measurements of the THz emission from GaAs1−xBix epilayers excited with femtosecond laser pulses (λ ∼ 800 nm). observed an increase in peak-to-peak amplitude electric field increasing Bi concentration. also a polarity reversal transient higher concentration (x ≳ 1.4%). Taking into account band gap reduction due to incorporation and excess energy carriers, our suggest that there is cross-over predominantly surface emitter at low concentrations ≲ 0.5%) photo-Dember

We report time resolved magneto-optical measurements in InMnSb ferromagnetic films with 2% and 2.8% Mn contents grown by low temperature molecular beam epitaxy. In order to probe a possible interaction between the spins of photoexcited carriers ions, we measured spin dynamics before after aligning ions applying an external magnetic field at temperatures above below samples’ Curie temperatures. observed no significant or dependence relaxation times attribute entirely electrons conduction band...

We investigate nonequilibrium acoustic phonon-assisted tunneling in a weakly coupled GaAs∕AlAs superlattice (SL). Previously it had been predicted that, such structures, the conditions for terahertz phonon amplification can be achieved [B. A. Glavin, V. Kochelap, and T. L. Linnik, Appl. Phys. Lett. 74, 3525 (1999)]. present experimental measurements of change current ΔI due to an incident pulse generated by thermalizing laser metal film. In particular, we measure dependence on angle...

We report on photoluminescence measurements of GaAs(1−x)Bix thin films containing dilute concentration (x≤0.045%) isoelectronic impurity Bi. At a temperature 4 K, we observed sharp emission line at ∼1.510 eV and series undulations in an energy range ∼20 meV below it. attribute the to recombination excitons bound complex formed by unintentionally incorporated acceptor or donor atoms samples. Undulations 1.510 are assigned vibronic levels acceptors, generated dynamic Jahn–Teller effect due...

We show that low temperature specific heat (C$_p$) of the incommensurate chain-ladder system Sr$_{14}$Cu$_{24}$O$_{41}$ is enriched by presence a rather large excess contribution non-magnetic origin. Diluted Al doping at Cu site or annealing crystal in an O$_2$ atmosphere suppresses this feature considerably. Using THz time-domain spectroscopy, we occurrence associated with very low-energy ($\sim$ 1 meV) gapped phonon modes originate due to sliding motion oppositely charged mutually chain...

We show the resonant behavior of \ensuremath{\sim}0.5-THz longitudinal acoustic (LA) phonons in an nanocavity thickness \ensuremath{\sim}28 nm sandwiched between two GaAs/AlAs superlattices (SLs). One SLs, upon excitation with ultrafast optical pulse, acts as a source coherent LA phonons. These phonons, generated outside cavity, resonantly drive cavity mode. The phonon dynamics can be modeled using driven-damped harmonic oscillator. confinement and enhancement opens up possibilities field...

We have generated pulses of $\ensuremath{\sim}0.5\mathrm{THz},$ monochromatic transverse-polarized acoustic (TA) phonons by resonant excitation a (001) GaAs/AlAs superlattice (SL) structure using femtosecond optical pulses. The were detected superconducting bolometers. Spectral resolution was obtained the filter effect frequency-dependent phonon scattering in GaAs substrate and also second as notch placed between generator bolometer. propose that TA are due to leakage optically excited...