Effect of the InAlAs and InGaAs combination strain-reducing layer on 1.3 mu m emission self-assembled InAs/GaAs quantum dots

Self-assembled InAs quantum dots (QDs) with differing deposition thicknesses covered by InxAl1-xAs (x = 0.2, 0.3) and In0.2Ga0.8As combination strain-reducing layers (CSRLs) were grown by molecular beam epitaxy. Their structural and optical properties were investigated by atomic force microscopy and photoluminescence spectroscopy, respectively. The emission peak position of InAs QDs capped by CSRL can reach 1.34 mum at room temperature with a relatively larger energy splitting of 93 meV between the ground and first excited states.

Dependence of elastic strain field on the self-organized ordering of quantum dot superlattices

A systematic investigation of the strain distribution of self-organized, lens-shaped quantum dot in the case of growth direction on (001) substrate was presented. The three-dimensional finite element analysis for an array of dots was used for the strain calculation. The dependence of the strain energy density distribution on the thickness of the capping layer was investigated in detail when the elastic characteristics of the matrix material were anisotropic. It is shown that the elastic anisotropic greatly influences the stress, strain, and strain energy density in the quantum dot structures. The anisotropic ratio of the matrix material and the combination with different thicknesses of the capping layer, may lead to different strain energy density minimum locations on the capping layer surface, which can result in various vertical ordering phenomena for the next layer of quantum dots, i.e. partial alignment, random alignment, and complete alignment.

The research and progress of micro-fabrication technologies of two-dimensional photonic crystal

The novel material of photonic crystal makes it possible to control a photon, and the photonic integration will have breakthrough progress due to the application of photonic crystal. It is based on the photonic crystal device that the photonic crystal integration could be realized. Therefore, we should first investigate photonic crystal devices based on the active and the passive semiconductor materials, which may have great potential application in photonic integration. The most practical and important method to fabricate two-dimensional photonic crystal is the micro-manufacture method. In this paper, we summarize and evaluate the fabrication methods of two-dimensional photonic crystal in near-infrared region, including electron beam lithography, selection of mask, dry etching, and some works of ours. This will be beneficial to the study of the photonic crystal in China.

Exciton energy of the InAs/GaAs self-assembled quantum dot in a semiconductor microcavity

We report on the theoretical study of the interaction of the quantum dot (QD) exciton with the photon waveguide models in a semiconductor microcavity. The InAs/GaAs self-assembled QD exciton energies are calculated in a microcavity. The calculated results reveal that the electromagnetic field reduces the exciton energies in a semiconductor microcavity. The effect of the electromagnetic field decreases as the radius of the QD increases. Our calculated results are useful for designing and fabricating photoelectron devices.

Analysis of the temperature-induced transition to current self-oscillations in doped GaAs/AlAs superlattices

We observed the decrease of the hysteresis effect and the transition from the stable to the dynamic domain regime in doped superlattices with increasing temperature. The current-voltage characteristics and the behaviours of the domain boundary are dominated by the temperature-dependent lineshape of the electric field dependence of the drift velocity (V(F)), As the peak-valley ratio in the V(F) curve decreases with increasing temperature, the hysteresis will diminish and temporal current self-oscillations will occur. The simulated calculation, which takes the difference in V(F) curves into consideration, gives a good agreement with the experimental results.

Effects of seed layer on the realization of larger self-assembled coherent InAs/GaAs quantum dots

The size and shape evolution of self-assembled InAs quantum dots (QDs) influenced by 2.0 ML InAs seed layer has been systematically investigated for 2.0, 2.5, and 2.9 ML deposition on GaAs(100) substrate. Based on comparisons with the formation of large incoherent InAs islands on single-layer samples at late growth stage, the larger coherent InAs quantum dots at 2.9 ML deposition has been observed on the second InAs layer. A simple model analysis accounting for the surface strain distribution influenced by buried islands gives a stronger increment of critical QD diameter for dislocation nucleation on the second layer in comparison with the single-layer samples. Additionally, the inhibition of dislocation nucleation in InGaAs/GaAs large islands can also be explained by our theoretical results. (C) 2000 American Institute of Physics. [S0021-8979(00)08922-2].

Anomaly of the current self-oscillation frequency in the sequential tunneling of a doped GaAs/AlAs superlattice

An anomalous behavior of the current self-oscillation frequency is observed in the dynamic de voltage bands, emerging from each sawtoothlike branch of the current-voltage characteristic of a doped GaAs/A1As superlattice in the transition process from static to dynamic electric field domain formations. Varying the applied de voltage at a fixed temperature, we find that the frequency increases while the averaged current decreases. Inside each voltage band, the frequency has a strong voltage dependence in the temperature range where the averaged current changes with the applied de voltage. This dependence can be understood in terms of motion of the system along a limit cycle.

Temperature and excitation power dependence of the optical properties of InAs self-assembled quantum dots grown between two Al0.5Ga0.5As confining layers

We have investigated the temperature and excitation power dependence of photoluminescence properties of InAs self-assembled quantum dots grown between two Al0.5Ga0.5As quantum wells. The temperature evolutions of the lower-and higher-energy transition in the photoluminescence spectra have been observed. The striking result is that a higher-energy peak appears at 105 K and its relative intensity increases with temperature in the 105-291 K range. We demonstrate that the higher-energy peak corresponds to the excited-state transition involving the bound-electron state of quantum dots and the two-dimensional hole continuum of wetting layer. At higher temperature, the carrier transition associated with the wetting layer dominates the photoluminescence spectra. A thermalization model is given to explain the process of hole thermal transfer between wetting layer and quantum dots. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

Temperature dependence of the optical properties of InAs/GaAs self-organized quantum dots with bimodal size distribution

In this work we report the optical and microscopic properties of self-organized InAs/GaAs quantum dots grown by molecular beam epitaxy on (1 0 0) oriented GaAs substrates. A distinctive double-peak feature of the PL spectra from quantum dots has been observed, and a bimodal distribution of dot sizes has also been confirmed by scanning tunneling microscopy (STM) image for uncapped sample. The power-dependent photoluminescence (PL) study demonstrates that the distinctive PL emission peaks are associated with the ground-state emission of islands in different size branches. The temperature-dependent PL study shows that the PL quenching temperature for different dot families is different. It is shown that the coupling between quantum dots plays a key role in unusual temperature dependence of QD photoluminescence. In addition, we have tuned the emission wavelength of InAs QDs to 1.3 mu m at room temperature. (C) 2000 Elsevier Science B.V. All rights reserved.

Effect of dopant on the uniformity of InAs self-organized quantum dots

Low-temperature photoluminescence studies have been performed on Si-doped and Be-doped self-organized InAs/GaAs quantum dot (QD) samples to investigate the effect of doping. When Si or Be is doped into the sample, a remarkable decrease in line-width is observed. We relate this phenomenon to a model that takes the Si or Be atoms as the nucleation centers for the formation of QDs. When Si or Be is doped, more small uniform quantum dots are formed. The result will be of significance for the application of self-organized InAs quantum dots in semiconductor devices.

Self-organization of the InGaAs GaAs quantum dots superlattice

The mechanism of self-organization of quantum dots (QDs) during the growth of InGaAs/GaAs multilayers on GaAs (1 0 0) was investigated with cross-sectional transmission electron microscopy (XTEM), and double-crystal X-ray diffraction (DCXD). We found that the QDs spacing in the first layer can affect the vertical alignment of QDs. There seems to exist one critical lateral QD spacing, below which merging of QDs with different initial size is found to be the dominant mechanism leading to perfect vertical alignment. Once the critical value of QDs spacing is reached, the InGaAs QDs of the first layer are simply reproduced in the upper layers. The X-ray rocking curve clearly shows two sets of satellite peaks, which correspond to the QDs superlattice, and multi-quantum wells (QW) formed by the wetting layers around QDs. (C) 1999 Elsevier Science B.V. All rights reserved.

Self-organization of the InGaAs GaAs quantum dots superlattice

The mechanism of self-organization of quantum dots (QDs) during the growth of InGaAs/GaAs multilayers on GaAs (1 0 0) was investigated with cross-sectional transmission electron microscopy (XTEM), and double-crystal X-ray diffraction (DCXD). We found that the QDs spacing in the first layer can affect the vertical alignment of QDs. There seems to exist one critical lateral QD spacing, below which merging of QDs with different initial size is found to be the dominant mechanism leading to perfect vertical alignment. Once the critical value of QDs spacing is reached, the InGaAs QDs of the first layer are simply reproduced in the upper layers. The X-ray rocking curve clearly shows two sets of satellite peaks, which correspond to the QDs superlattice, and multi-quantum wells (QW) formed by the wetting layers around QDs. (C) 1999 Elsevier Science B.V. All rights reserved.

Self-Assembly of Rod-Terminally Tethered Three-Armed Star-Shaped Coil Block Copolymer: Investigation of the Presence of the Branching in the Coil to the Self-Assembled Behavior

Self-assembled behavior of rod-terminally tethered three-armed star-shaped coil block copolymer melts was studied by applying self-consistent-field lattice techniques in three-dimensional (3D) space. Similar to rod-coil diblock copolymers, five morphologies were observed, i.e., lamellar, perforated lamellar, gyroidlike, cylindrical and sphericallike structures, while the distribution of the morphologies in the phase diagram was dramatically changed with respect to that Of rod-coil diblock copolymers.