Influence of interdot electronic coupling on photoluminescence spectra of self-assembled InAs/GaAs quantum dots

The influence of interdot electronic coupling on photoluminescence (PL) spectra of self-assembled InAs/GaAs quantum dots (QDs) has been systematically investigated combining with the measurement of transmission electron microscopy. The experimentally observed fast red-shift of PL energy and an anomalous reduction of the linewidth with increasing temperature indicate that the QD ensemble can be regarded as a coupled system. The study of multilayer vertically coupled QD structures shows that a red-shift of PL peak energy and a reduction of PL linewidth are expected as the number of QD layers is increased. On the other hand, two layer QDs with different sizes have been grown according to the mechanism of a vertically correlated arrangement. However, only one PL peak related to the large QD ensemble has been observed due to the strong coupling in InAs pairs. A new possible mechanism to reduce the PL linewidth of QD ensemble is also discussed.

Growth mechanism of InGaAlAs waveguides by narrow stripe selective MOVPE

Growth mechanism of InGaAlAs waveguides by narrow stripe selective MOVPE has been studied. Both the InGaAlAs bulk waveguides and the InGaAlAs MQW waveguides were successful grown on the patterned substrates at optimized growth conditions. The mask stripe width varied from 0 to 40 mu m, while the window region width between a pair of mask stripes was fixed 2.5 mu m. These selectively grown waveguides were covered by specific InP layers, which can keep the InGaAlAs waveguides from being oxidized during the fabrication of devices. In particular, there exhibit strong dependences of the photoluminescence (PL) spectrum on the mask stripe width for the samples. The results were explained in considering both the migration effect from a masked region (MMR) and the lateral vapor diffusion effect (LVD).

Short range scattering mechanism of type-II GaSb/GaAs quantum dots on the transport properties of two-dimensional electron gas

We have studied the scattering process of AlGaAs/GaAs two-dimensional electron gas with the nearby embedded GaSb/GaAs type-II quantum dots (QDs) at low temperature. Quantum Hall effect and Shubnikov-de Haas oscillation were performed to measure the electron density n(2D), the transport lifetime tau(t) and the quantum lifetime tau(q) under various biased gate voltage. By comparing measured results of QDs sample with that of reference sample without embedded QDs, mobilities (transport mobility mu(t) and quantum mobility mu(q)) dominated by GaSb QDs scattering were extracted as functions of n(2D). It was found that the ratios of tau(t) to tau(q) were varying within the range of 1-4, implying the scattering mechanism belonging to the sort of short-range interaction. In the framework of Born approximation, a scattering model considering rectangular-shaped potential with constant barrier height was successfully applied to explain the transport experimental data. In addition, an oscillating ratio of tau(t)/tau(q) with the increasing n(2D) was predicted in the model.

Enhanced photoluminescence of Nd2O3 nanoparticles modified with silane-coupling agent: Fluorescent resonance energy transfer analysis

A liquid laser medium with a lifetime of 492 mu s and a fluorescent quantum efficiency of 52.5% has been presented by stably dispersing dimethyl dichorosilane-modified Nd2O3 nanoparticles in dimethylsulfoxide. Its optical properties and mechanism were investigated and explained by fluorescence resonance energy transfer theory. The calculation result shows that the quenching of Nd-III F-4(3/2)-> I-4(11/2) transition via O-H vibrational excitation can be eventually neglected. The main reason is that the silane-coupling agent molecules remove the -OH groups on Nd2O3 nanoparticles and form a protective out layer. (c) 2007 American Institute of Physics.

PHOTOLUMINESCENCE INVESTIGATIONS OF CD1-XMNXTE UNDER HYDROSTATIC-PRESSURE

The photoluminescence of Cd1-xMnxTe with x=0.25, 0.40, and 0.60 is investigated at 77 K and different pressures. The pressure coefficients of the photoluminescence bands Cd0.75Mn0.25Te and Cd0.6Mn0.4Te are found to be positive and the magnitudes are about 8 X 10(-3) eV/kbar, which is in good agreement with the pressure coefficients of the interband transition. The pressure coefficient of the photoluminescence bands for Cd0.4Mn0.6Te is found to be -6 X 10(-3) eV/kbar, which is quite different from the pressure coefficient of the interband transition. The possible transition mechanism is discussed in terms of group theory and crystal field theory.

Photoluminescence enhancement of (NH4)(2)S-x passivated InP surface by rapid thermal annealing

Photoluminescence enhancement of (NH4)(2)S-x passivated InP surface followed by rapid thermal annealing (RTA) has been investigated by using photoluminescence (PL), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS), An increase in PL intensity of up to 10 times was observed after sulfur passivation and RTA treatment compared to unpassivated InP surface. XPS measurement results show that introduction of RTA process can enhance the sulfur remaining on the passivated surface to bond to indium but no evidence of S-P bond is noticeable. Passivation enhancement mechanism is discussed.

Photoluminescence and activation on SI-GaAs by Si+ implantation and following rapid thermal annealing

Photoluminescence (PL) and electrical characteristics of SI-GaAs, Si+-implanted and following rapid thermal annealing (RTA), were investigated, The PL spectra of Si-GA-C-As, Ga-i-Si-As, and V-As-Si-As were obtained. This paper concentrates on the PL peak at 1.36 eV which was proven as an emission of the Si-Ga-V-Ga combination by Si+ + P+ dual implantation. The results indicate that the peak at 1.36 eV appears when the ratio of As:Ga increased during the processing. Also high activation was obtained for the sample under the same conditions. More discussion on the mechanism of Si+ implanted SI-GaAs has been made based on the Morrow model [J. Appl. Phys, 64 (1988) 1889].

PHOTOLUMINESCENCE SPECTRUM STUDY OF THE GAAS/SI EPILAYER GROWN BY USING A THIN AMORPHOUS SI FILM AS BUFFER LAYER

Recently, we reported successful growth of high-quality GaAs/Si epilayers by using a very thin amorphous Si film as buffer layer. In this paper, the impurity properties of this kind of GaAs/Si epilayers have been studied by using PL spectrum, SIMS and Hall measurement. Compared to a typical PL spectrum of the GaAs/Si epilayers grown by conventional two-step method, a new peak was observed in our PL spectrum at the energy of 1.462 eV, which is assigned to the band-to-silicon acceptor recombination. The SIMS analysis indicates that the silicon concentration in this kind of GaAs/Si epilayers is about 10(18) cm(-3). But its carrier concentration (about 4 x 10(17) cm(-3)) is lower than the silicon concentration. The lower carrier concentration in this kind of GaAs/Si epilayer can be interpreted both as the result of higher compensation and as the result of the formation of the donor-defect complex. We also found that the high-quality and low-Si-concentration GaAs/Si epilayers can be regrown by using this kind of GaAs/Si epilayer as substrate. The FWHM of the X-ray (004) rocking curve from this regrowth GaAs epilayer is 118 '', it is much less than that of the first growth GaAs epilayer (160 '') and other reports for the GaAs/Si epilayer grown by using conventional two-step method (similar to 200 '').

Yellow luminescence mechanism and persistent photoconductivity in n-GaN single crystal films grown on alpha-Al2O3(0001) substrates by LP-MOCVD

Unintentionally doped and Si-doped single crystal n-GaN films have been grown on alpha-Al2O3 (0001) substrates by LP-MOCVD. Room temperature photoluminescence measurement showed that besides the bandedges, the spectrum of an undoped sample was a broad deep-level emission band peaking from 2.19 to 2.30eV, whereas the spectrum for a Si-doped sample was composed of a dominant peak of 2.19eV and a shoulder of 2.32eV. At different temperatures, photoconductance buildup and its decay were also observed for both samples.. The likely origins of persistent photoconductivity and yellow luminescence, which might be associated with deep defects inclusive of either Ga vacancy(V-Ga)/Ga vacancy complex induced by impurities or N antisite (N-Ga), will be proposed.

Mechanism on exciton-mediated energy transfer in erbium-doped silicon

Exciton-mediated energy transfer model in Er-doped silicon was presented. The emission intensity is related to optically active Er concentration, lifetime of excited Er3+ ion and spontaneous emission. The thermal quenching of the Er luminescence in Si is caused by thermal ionization of Er-bound exciton complex and nonradiative energy back-transfer processes, which correspond to the activation energy of 6.6 and 47.4 meV, respectively. Er doping in silicon introduces donor states, a large enhancement in the electrical activation of Er (up to two orders of magnitude) is obtained by co-implanting Er with O. It appears that the donor states are the gateway to the optically active Er. (C) 2000 Elsevier Science B.V. All rights reserved.

Influence of interdot electronic coupling on photoluminescence spectra of self-assembled InAs/GaAs quantum dots

The influence of interdot electronic coupling on photoluminescence (PL) spectra of self-assembled InAs/GaAs quantum dots (QDs) has been systematically investigated combining with the measurement of transmission electron microscopy. The experimentally observed fast red-shift of PL energy and an anomalous reduction of the linewidth with increasing temperature indicate that the QD ensemble can be regarded as a coupled system. The study of multilayer vertically coupled QD structures shows that a red-shift of PL peak energy and a reduction of PL linewidth are expected as the number of QD layers is increased. On the other hand, two layer QDs with different sizes have been grown according to the mechanism of a vertically correlated arrangement. However, only one PL peak related to the large QD ensemble has been observed due to the strong coupling in InAs pairs. A new possible mechanism to reduce the PL linewidth of QD ensemble is also discussed.

Photoluminescence of inert-gas ion implanted sapphire after 230-MeV Pb ion irradiation

In the present work the photoluminescence (PL) character of sapphire implanted with 110-keV He, Ar or Ne ions and subsequently irradiated with 230-MeV Pb was studied. The implantation was performed at 320 and 600 K using fluences from 5.0 x 10(16) to 2.0 x 10(17) ions/cm(2). The Pb ion irradiation was carried out at 320 K. The obtained PL spectra showed peaks at 375, 413 and 450 nm with maximum intensity at an implantation fluence of 5.0 x 10(16) ions/cm(2) and a new peak at 390 nm appeared in the He-implanted and subsequently Pb-irradiated samples. Infrared spectra showed a broadening of the absorption band between 460 and 510 nm indicating strongly damaged regions formed in the Al2O3 samples. A possible PL mechanism is discussed.

Self-assembled 3D Architectures of LuBO3 : Eu3+: Phase-selective synthesis, growth mechanism, and tunable luminescent properties

Rhombohedral-calcite and hexagonal-vaterite types of LuBO:Eu3+ microparticles with various complex self-assembled 3D architectures have been prepared selectively by an efficient surfactant- and template-free hydrothermal process for the first time. X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectrometry, transmission electron microscopy, high-resolution transmission electron microscopy, selected area electron diffraction, photoluminescence, and cathodoluminescence spectra as well as kinetic decays were used to characterize the samples.

SrF2 hierarchical flowerlike structures: Solvothermal synthesis, formation mechanism, and optical properties

We present a solvothermal route to the synthesis of SrF2 hierarchical flowerlike structures based on thermal decomposition of single source precursor (SSP) of strontium trifluoroacetate in benzylamine solvent. These flowerlike superstructures are actually composed of numerous aggregated nanoplates, and the growth process involves the initial formation of spherical nanoparticles and subsequent transformation into nanoplates. which aggregated together to form microdisks and finally flowerlike superstructures. The results demonstrate the important role of benzylamine in the formation of well-defined SrF2 superstructures, not only providing size and shape control to form nanoplates but also contributing to the self-assembly behavior of nanoplates to build into flower-like superstructures. Additionally, the photoluminescence properties of the obtained SrF2 superstructures are studied.

Anticancer Drug-DNA Interactions Measured Using a Photoinduced Electron-Transfer Mechanism Based on Luminescent Quantum Dots

A sensing system based on the photoinduced electron transfer of quantum dots (QDs) was designed to measure the interaction of anticancer drug and DNA, taking mitoxantrone (MTX) as a model drug. MTX adsorbed on the surface of QDs can quench the photoluminescence (PL) of QDs through the photoinduced electron-transfer process; and then the addition of DNA will bring the restoration of QDs PL intensity, as DNA can bind with MTX and remove it from QDs. Sensitive detection of MTX with the detection limit of 10 nmol L-1 and a linear detection range from 10 nmol L-1 to 4.5 mu mol L-1 was achieved. The dependence of PL intensity on DNA amount was successfully utilized to investigate the interactions between MTX and DNA. Both the binding constants and the sizes of binding site of MTX-DNA interactions were calculated based on the equations deduced for the PL recovery process. The binding constant obtained in our experiment was generally consistent with previous reports. The sensitive and speedy detection of MTX as well as the avoidance of modification or immobilization process made this system suitable and promising in the drug-DNA interaction studies.