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In this paper, we have investigated the effect of Be acceptors on the electroluminescence and the spin polarization in GaAs/AlAs p-i-n resonant tunneling diodes. The quantum well emission comprise two main lines separated by ~20meV attributed to excitonic and Be-related transitions, which intensities show remarkably abrupt variations at critical voltages, particularly at the electron resonant peak where it shows a high-frequency bistability. The circular-polarization degree of the quantum-well electroluminescence also shows strong and abrupt variations at the critical bias voltages and it attains relatively large values (of ~–75% at 15 T). These effects may be explored to design novel devices for spintronic applications such as a high-frequency spin-oscillators. [ABSTRACT FROM AUTHOR]

We report on the crystal morphology and Raman scattering features of high structural quality GaSb1−xBix alloys grown by molecular beam epitaxy with a high Bi content (x up to ∼0.10). The Raman spectra were measured at room temperature with different laser excitation wavelengths of 532 nm, 633 nm, and 785 nm. We observed well-defined Bi-induced Raman peaks associated with atomic Bin clusters and GaBi vibrational modes. Remarkably, some Bi-induced Raman modes were strongly enhanced when the laser energy was selected near an optical transition for the 5.8%Bi sample. This effect was attributed to a Raman resonant effect near an excited optical transition of the GaSbBi layer and has been used to identify the nature of the observed Raman peaks. [ABSTRACT FROM AUTHOR]

The combination of photoluminescence and magneto-transport measurements is used to study the single-particle relaxation time and the transport scattering time in short-period InGaAs/InP superlattices. Both the single-particle relaxation times of the electrons and of the holes were obtained in the same samples and were shown to be determined by the remote-impurity scattering. The transport scattering time for electrons was found to be dominated by the interface-roughness scattering with lateral length Λ=10 nm and height Δ = 0.13 nm. We also discuss the importance of multiple-scattering effects for small well widths and of alloy scattering for large well widths. [ABSTRACT FROM AUTHOR]

We have investigated the spin properties of a two-dimensional hole gas (2DHG) formed at the contact layer of a p-type GaAs/AlAs resonant tunneling diode (RTD). We have measured the polarized-resolved photoluminescence of the RTD as a function of bias voltage, laser intensity and external magnetic field up to 15T. By tuning the voltage and the laser intensity, we are able to change the spin-splitting from the 2DHG from almost 0 meV to 5 meV and its polarization degree from − 40% to + 50% at 15T. These results are attributed to changes of the local electric field applied to the two-dimensional gas which affects the valence band and the hole Rashba spin-orbit effect. [ABSTRACT FROM AUTHOR]

Optical properties of diluted magnetic semiconductor Ga0.999Mn0.001As/AlAs quantum well structures grown on (1 0 0 ), (1 1 0), (3 1 1)B and (4 1 1)B by molecular beam epitaxy are reported. Temperature-dependent spectral photoluminescence (PL) measurement was performed at temperatures between 15 and 300 K. The PL measurements showed that band gap of the alloy decreases with increasing lattice temperature regardless the growth orientations. S-shaped temperature dependence has been observed in the samples grown on (1 0 0), (3 1 1)B, (4 1 1)B orientations. PL emission energy is fitted with Varshni and Bose–Einstein Approximation to determine Debye temperature (β), (ΘE) and thermal expansion coefficient (α), the exciton–phonon coupling strength (aB). [ABSTRACT FROM AUTHOR]

We investigated excitonic absorptions in a GaAs/AlAs/GaAs single barrier heterostructure using both photocapacitance and photocurrent spectroscopies at room temperature. Photocapacitance spectra show well defined resonance peaks of indirect excitons formed around the Γ-AlAs barrier. Unlike DC-photocurrent spectra, frequency dependent photocapacitance spectra interestingly red shift, sharpen up, and then decrease with increasing tunneling at higher biases. Such dissimilarities clearly point out that different exciton dynamics govern these two spectral measurements. We also argue why such quantum confined dipoles of indirect excitons can have thermodynamically finite probabilities to survive even at room temperature. Finally, our observations demonstrate that the photocapacitance technique, which was seldom used to detect excitons in the past, is useful for selective detection and experimental tuning of relatively small numbers (∼1011/cm2) of photo-generated indirect excitons having large effective dipole moments in this type of quasi-two dimensional heterostructures. [ABSTRACT FROM AUTHOR]

We have investigated the polarized-resolved photoluminescence from the contact layers and the quantum-well in an n-type GaAs/GaAlAs resonant tunneling diode for magnetic fields up to 19 T. The optical emission from the GaAs contact layers comprises the recombination from highly spin-polarized two-dimensional electron and hole gases with free tunneling carriers. Both the energy position and intensity of this indirect recombination are voltage-dependent and show remarkably abrupt variations near scattering-assisted tunneling resonances. Our results show that these two dimensional gases act as spin-polarized sources for carriers tunneling through the well in resonant tunneling diodes. [ABSTRACT FROM AUTHOR]

In this work, we have reported an enhancement of the photoluminescence intensity in Poly(3-thiopheneacetic acid), PTAA, films irradiated by laser in air. This effect depends on the laser intensity, exposure time and sample thickness. It was observed an increase of the luminescence intensity up to 110% without any significant shift in PL peak position. Our results suggest that a partial degradation process occurs in the sample, which confines the charge carriers in a narrower region of the film increasing the probability of radioactive decay. [ABSTRACT FROM AUTHOR]

The photoluminescence (PL) behaviour of PVA-PTAA blends of different composition is investigated. It is observed that the interchain interaction have an important effect in this system leading to an unexpected decrease in the PL intensity as the PTAA content increase. An enhancement of the PL intensity as function of the time was also detected for all samples which were irradiated by laser. Using laser intensity of 18 W/cm 2 it was observed an increase of 93% in PVA-PTAA 1 wt% blend. Using this methodology it was possible to build an emission pattern. [ABSTRACT FROM AUTHOR]

We have investigated the polarized emission from a n-type GaAs/AlGaAs resonant tunneling diode under magnetic field. The GaAs contact layer emission shows a large constant negative circular polarization. A similar result is observed for the quantum well, but only when electrons are injected from the substrate, while for inverted biases, the polarization tends to become positive for small voltages and large laser excitation intensities. We believe that the quantum well polarization may be associated to the partial thermalization of minority carriers on the well subbands and is thus critically dependent on the bias-controlled density of carriers accumulated in the well. [ABSTRACT FROM AUTHOR]

The authors have observed a strong dependence of the circular polarization degree from the quantum well emission in an asymmetric n-type GaAs/AlAs/AlGaAs resonant tunneling diode on both the laser excitation intensity and the applied bias voltage. The sign of the circular polarization can be reversed by increasing the light excitation intensity when the structure is biased with voltages slightly larger than the first electron resonance. The variation of polarization is associated with a large density of photogenerated holes accumulated in the quantum well, which is enhanced due to the asymmetry of the structure. [ABSTRACT FROM AUTHOR]

The authors investigate the circular polarization of the electro- and photoluminescence emissions from the quantum well and contact layers of a nonmagnetic GaAs–AlAs p-i-n resonant tunneling diode under an external magnetic field. The contact emission evidences the formation of a spin polarized two-dimensional electron gas at the n-accumulation layer. The quantum well electroluminescence presents a strong σ- degree of polarization, even for null Zeeman splitting energies, and a slight bias dependence. The observed circular polarization is mainly attributed to the spin polarization of the electrons injected into the quantum well from the two-dimensional electron gas. [ABSTRACT FROM AUTHOR]