J.M.R. Cruz

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.

Carrier kinetics in quantum dots through continuous wave photoluminescence modeling: A systematic study on a sample with surface dot density gradient

A systematic study is presented of continuous wave (cw) photoluminescence (PL) of self-assembled quantum dots (QDs) grown on GaAs (001) by molecular-beam epitaxy as a function of excitation intensity and QD density. The sample used in this work was grown under nonisotropic indium flux that resulted in a QD density gradient across the sample surface ranging from 0 to 1.8×1011 cm−2. The carrier kinetics in the sample is described by a set of coupled rate equations through which the cw PL data from the GaAs barrier, wetting layer (WL), and QDs were simulated as a function of the excitation intensity and QD density. By comparing the PL data with our simulations we infer that carrier capture into the QD occurs directly from GaAs barrier. Auger and phonon-assisted carrier capture from the WL were found to give negligible contribution. With an increase of the QD density we observe an increase of the nonradiative recombination rates of the barrier and at the WL, which we tentatively correlate with the increase of...

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.

Asymmetric carrier transport in InGaAs quantum wells and wires grown on tilted InP substrates

Abstract The influence of the interface morphology upon the electron–hole transport in intrinsic In 0.53 Ga 0.47 As/InP quantum structures was investigated by scanning the photoluminescence PL intensity profile on the sample surface. The results suggest that the carrier diffusion is very sensitive to both 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.

Photoexcited carrier diffusion in self-assembled InAs/GaAs quantum dots with different dot densities

Abstract The carrier dynamics in self-assembled InAs/GaAs quantum dots (QDs) has been investigated as a function of the lateral dot density. We investigated the influence of the QD density on the process of carrier transfer among the QDs. We have found evidence that potential barriers at the wetting layer and dot interfaces are responsible to decrease the carrier capture in low density QDs. This effect can be observed on the increased carrier transport.

Photoquenching indications of a thermally triggered transition between two different EL2 metastable states in GaAs

In this work we report the observation of two different EL2 metastable states in GaAs and the effect of the optical/thermal history of the sample on the behavior of the photoquenching kinetics. In one thermal/optical preparation, the photoquenching curve presented two time constants that have already been interpreted as an indication of two different metastable states. With another preparation, the initial rise in transmittance displayed only one time constant, and we observed that a temperature increase to 83K triggered a second photoquenching process. We associated this new photoquenching with a transition from the first to the second metastable state. The experimental data is explained in terms of a new proposal for the microscopic structure of the EL2 complex.

Observation of the spectral dependence of the spatial photocarrier redistribution in InAs/GaAs quantum dots

Abstract In this work we have studied the behavior of the spatial photocarrier distribution in InAs/GaAs self-assembled QDs as a function of the emission energy. Our results show that the spread of this distribution presents an energy dependence very similar to the observed spectral dependence of the photoluminescence (PL) decay time obtained by time resolved experiments.