A. F. G. Monte

An experimental design for microluminescence

The description of a new experimental design for microluminescence is presented in this article. The design is based on the optical analysis of a magnified luminescent region and has been proven to be useful for studying the photon transport mechanism in a solid luminescent material. Lock-in detection and a liquid-nitrogen-cooled detector are used to obtain signal-to-noise ratio as good as 102. The performance of the system is discussed by using the measurements taken from a natural ruby crystal. Using transport theory to fit our data, we found the photon diffusion length in the ruby crystal to be on the order of 46 μm.

SPATIAL AND TEMPERATURE DEPENDENCE OF CARRIER RECOMBINATION IN AN INGAAS/INP HETEROSTRUCTURE

The microluminescence surface scan technique has been used to investigate ambipolar carrier diffusion, photon diffusion, and photocarrier recombination in a nominally undoped InGaAs bulk layer lattice matched to InP grown by vapor levitation epitaxy. Measurements taken at different temperatures between 75 and 300 K are discussed in terms of the relative contribution of the two distinct mechanisms to the spectrally integrated luminescence intensity, namely, photon diffusion and photocarrier diffusion.

Growth and characterisation of ZnO quantum dots in polyacrylamide

ZnO nanocrystals were successfully fabricated by wet-chemical method. Optical properties of excitons confined in ZnO nanocrystals were studied by measuring both optical absorption and photoluminescence spectra. Absorption due to free excitons was clearly observed whereas strong PL lines were recorded in the UV region at around the exciton absorption energy. Red-shift of optical features with increasing annealing time indicates an increase in quantum dot size.

Mean free path for excitation energy migration in Nd3+-doped glasses as a function of concentration

The energy-transfer process and the related migration mechanism of excitation energy, important in the optical dynamics of Nd-doped glasses, were investigated. In order to study the migration mechanism and transfer process, Nd3+-doped oxide glasses were produced with doping concentration (N) ranging from 0.1to1.9wt% as Nd2O3. A microluminescence technique was used to measure the spatial distribution of the emitting light as a function of the distance from the center of the laser-excitation spot with different Nd3+-ion concentrations. Efficient long-range migration of excitation energy of Nd3+ ions was observed at 1.1wt% of Nd2O3. The critical distance between Nd3+ ions, estimated from the observed migration length, shows that dipole-dipole interaction is not the dominant mechanism for energy transfer. The mean free path for migratory excitation energy in the investigated material, assisted by absorption and scattering by defects or phonons, is the most probable mechanism for energy transfer.

Synthesis and characterization of PbS quantum dots embedded in oxide glass

The fusion method was used to produce PbS quantum dots (QDs) embedded in S-doped glass matrix (SiO2-Na2CO3-Al2O3-PbO2-B2O3:S). Measurements of optical absorption (OA), photoluminescence (PL) and atomic force microscopy (AFM) have been carried out in order to characterize the produced QDs. A strong red-shift observed in the optical features with an increase of the annealing time indicates an increase in QD-size. The QD sizes predicted by k.p theoretical results were confirmed by AFM observation.

Symmetric and asymmetric fractal diffusion of electron–hole plasmas in semiconductor quantum wells

Abstract The diffusion of photogenerated electron–hole plasmas in intrinsic InP/InGaAs/InP single quantum wells was investigated by measurements of the photoluminescence intensity profile around the illuminated area. Two kinds of heterostructures were investigated, one grown on InP substrate with the growth face orthogonal to the [001] direction, and the other grown on InP substrate two degrees off that orientation. The data show that the particles present a fractal diffusion described by the Levy distribution with the exponent parameter α =1.3. In the tilted heterostructure, the diffusion is asymmetric and the particles density obeys a generalized Levy distribution recently predicted by Chaves [Phys. Lett. A 239 (1998) 13].

Experimental evidence of asymmetric carrier transport in InGaAs quantum wells and wires grown on tilted InP substrates

The influence of the interface morphology upon the electron–hole transport in intrinsic In0.53Ga0.47As/InP quantum structures was investigated by scanning the photoluminescence intensity profile on the sample surface. The results suggest that the carrier diffusion is very sensitive both to the roughness of the interfaces and the presence of finite-width terraces. It was found that the carrier density profile shows asymmetric diffusion normal to the terraces whereas it shows symmetric expansion along the terraces. Simulations of the asymmetry in the carrier density profile using a non-Fickian diffusion equation described by the Levy statistics show a excellent agreement with the experimental data.

Defect-limited carrier diffusion in In0.53Ga0.47As-InP single quantum well

Abstract The diffusion of electron–hole plasma in an intrinsic In0.53Ga0.47As single quantum well (SQW) was investigated by measurements of the PL intensity profile around the illuminated area. We found that the carrier diffusion length increases with the temperature, from 85 to 300 K, according to a defect-limited carrier diffusion. A change in the carrier expansion is observed at about 200 K, which appears to be correlated with the thermal activation of a defect center with activation energy of 120 meV. An Arrhenius function of the PL emission intensity confirms that a nonradiative recombination channel becomes visible with an energy of about 120 meV.

Nonlinear effects of the photocurrent in self-assembled InAs/GaAs quantum dots

We report photocurrent (PC) and its complemented photoluminescence investigations of carrier escape dynamics in multi-layered InAs/GaAs self-assembled quantum dots (QDs) subjected to vertical electric fields. We found a nonlinear dependence of PC on the laser excitation power. This unusual behavior can be tuned by bias voltage. Very well agreement between PC data and theoretical prediction ensures that the accumulation of holes trapped in QDs is responsible for this nonlinearity. It is expected that this laser controlled electronic transport might open many potential applications in optoelectronic devices.

Excitation Transfer through Quantum Dots Measured by Microluminescence: Dependence on the Quantum Dot Density

In this study, spatially resolved cw photoluminescence of self-assembled InAs quantum dots (QDs) on a GaAs matrix has been observed using the microluminescence surface scan technique. A sample containing QD densities from 0 up to 1600 dots/μm 2 was investigated. It was found that the QD density has a strong influence on the diffusion process and there is evidence of two different mechanisms operating at low and high QD concentration ranges that we interpret as photon recycling and interdot carrier tunneling, respectively.