Electrical and optical properties of InAs/GaAs quantum dots doped by high energy Mn implantation

Mn ions were doped into InAs/GaAs quantum dots samples by high energy. implantation and subsequent annealing. The optical and electric properties of the samples have been studied. The photoluminescence intensity of the samples annealed rapidly is stronger than that of the samples annealed for long time. By studying the relationship between the photoluminescence peaks and the implantation dose, it can be found that the photoluminescence peaks of the quantum dots show a blueshift firstly and then move to low energy with the implantation. dose increasing. The latter change in the photoluminescence peaks is probably attributed to that Mn ions entering the InAs quantum dots, which release the strain of the quantum dots. For the samples implanted by heavy dose (annealed rapidly) and the samples annealed for long time, the resistances versus temperature curves reveal anomalous peaks around 40 K.

Effects of rapid thermal annealing on the emission properties of highly uniform self-assembled InAs/GaAs quantum dots emitting at 1.3 mu m

The authors report the effects of rapid thermal annealing (RTA) on the emission properties of highly uniform self-assembled InAs quantum dots (QDs) emitting at 1.3 mu m grown on GaAs substrate by metal organic chemical vapor deposition. Postgrowth RTA experiments were performed under N-2 flow at temperatures ranging from 600 to 900 degrees C for 30 s using GaAs proximity capping. Surprisingly, in spite of the capping, large blueshifts in the emission peak (up to about 380 meV at 850 degrees C) were observed (even at low annealing temperatures) along with enhanced integrated photoluminescence (PL) intensities. Moreover, pronounced peak broadenings occurred at low annealing temperatures (< 700 degrees C), indicating that RTA does not always cause peak narrowing, as is typically observed with traditional QDs with large inhomogeneous PL linewidths. The mechanism behind the large peak blueshift was studied and found to be attributed to the as-grown QDs with large size, which cause a larger dot-barrier interface and greater strain in and near the QD regions, thereby greatly promoting Ga-In intermixing across the interface during RTA. The results reported here demonstrate that it is possible to significantly shift the emission peak of the QDs by RTA without any additional procedures, even at lower annealing temperatures. (c) 2007 American Institute of Physics.

Anomalous temperature dependence of photoluminescence peak energy in InAs/InAlAs/InP quantum dots

We have observed an unusual temperature sensitivity of the photoluminescence (PL) peak energy for InAs quantum dots grown on InAs quantum wires (QDOWs) on InP substrate. The net temperature shift of PL wavelength of the QDOWs ranges from 0.8 to -4. angstrom/degrees C depending upon the Si doping concentration in the samples. This unusual temperature behavior can be mainly ascribed to the stress amplification in the QDOWs when the thermal strain is transferred from the surrounding InAs wires. This offers an opportunity for realizing quantum dot laser devices with a temperature insensitive lasing wavelength. (c) 2006 Elsevier Ltd. All rights reserved.

Size and shape evolution of self-assembled coherent InAs/GaAs quantum dots influenced by seed layer

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(1 0 0) substrate. Based on comparisons with the evolution of InAs islands on single layer samples at late growth stage, the bimodal size distribution of InAs islands at 2.5-ML InAs coverage and the formation of larger InAs quantum dots at 2.9-ML deposition have been observed on the second InAs layer. The further cross-sectional transmission electron microscopy measurement indicates the larger InAs QDs: at 2.9-ML deposition on the second layer are free of dislocation. In addition, the interpretations for the size and shape evolution of InAs/GaAs QDs on the second layer will be presented. (C) 2001 Elsevier Science B.V. All lights reserved.

InAs self-assembled quantum dots grown on an InP (311)B substrate by molecular beam epitaxy

Self-assembled InAs quantum dots (QDs) have been grown by solid-source molecular beam epitaxy on a (311)B InP substrate. Transmission electron microscopy clearly shows that a high density of smaller InAs islands can be obtained by using such a high index substrate. After introducing a lattice-matched underlying In0.52Al0.24Ga0.24As layer, the InAs QDs are much more uniform in size and form two-dimensional well ordered arrays. The photoluminescence (PL) spectra also confirm that the InAs QDs grown on underlying In0.52Al0.24Ga0.24As have a better quality than those grown in the In0.52Al0.48As matrix. A simple calculation indicates that the redshift of the PL peak energy mainly results from InAs QDs on underlying In0.52Al0.24Ga0.24As of large size. (C) 2001 American Institute of Physics.

Effects of interdiffusion on the luminescence of InAs/GaAs quantum dots covered by InGaAs overgrowth layer

We have studied the effects of postgrowth rapid thermal annealing on the optical properties of 3-nm-height InAs/GaAs quantum dots covered by 3-nm-thick InxGa1-xAs (x = 0, 0.1, and 0.2) overgrowth layer. At higher annealing temperature (T greater than or equal to 750 degreesC), the photoluminescence peak of InGaAs layer has been observed at lower-energy side of the InAs quantum-dot peak. In addition, the blueshift in photoluminescence (PL) emission energy is found to he similar for all samples with increasing the annealing temperature from 650 to 850 degreesC. However, the trend of narrowing of photoluminescence linewidth is significantly different for InAs quantum dots with different In mole fractions in InGaAs overgrowth layer. These results suggest that the intermixing in the lateral direction plays an important role in helping to understand the modification of optical properties induced by rapid thermal annealing. (C) 2000 Elsevier Science B.V. All rights reserved.

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].

Influence of InxGa1-xAs (0 <= x <= 0.3) cap layer on structural and optical properties of self-assembled InAs/GaAs quantum dots

Optical and structural properties of self-organized InAs/GaAs quantum dots (QDs) with InxGa1-xAs or GaAs cover layers grown by molecular beam epitaxy (MBE) have been characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM) and photoluminescence (PL) measurements. The TEM and AFM images show that the surface stress of the InAs QDs was suppressed by overgrowth of a InxGa1-xAs covering layer on the top of the QDs and the uniformity of the QDs preserved. PL measurements reveal that red shifts of the PL emission due to the reduction of the surface strain of the InAs islands was observed and the temperature sensitivity of the PL emission energy was suppressed by overgrowth of InxGa1-xAs layers compared to that by overgrowth of GaAs layers.

Structural and optical properties of self-assembled InAs/GaAs quantum dots covered by InxGa1-xAs (0 <= x <= 0.3)

Optical and structural investigations of InAs quantum dots (QDs) covered by InxGa1-xAs (0 less than or equal to x less than or equal to 0.3) overgrowth layer have been systematically reported. The decrease of strain in the growth direction of InAs quantum dots covered by InGaAs layer instead of GaAs is demonstrated by transmission electron microscopy experiments. In addition, the atomic force microscopy measurement shows that the surface of InAs islands with 3-nm-thick In0.2Ga0.8As becomes flatter. However, the InGaAs islands nucleate on the top of quantum dots during the process of InAs islands covered with In0.3Ga0.7As. The significant redshift of the photoluminescence peak energy and reduction of photoluminescence linewidth of InAs quantum dots covered by InGaAs are observed. The energy gap change of InAs QDs covered by InGaAs could be explained in terms of reducing strain, suppressing compositional mixing, and increasing island height. (C) 2000 American Institute of Physics. [S0021-8979(00)04018-4].

Electronic characteristics of InAs self-assembled quantum dots

Deep-level transient spectroscopy and photoluminescence studies have been carried out on structures containing self-assembled InAs quantum dots formed in GaAs matrices. The use of n- and p-type GaAs matrices allows us to study separately electron and hole levels in the quantum dots by the deep-level transient spectroscopy technique. From analysis of deep-level transient spectroscopy measurements it follows that the quantum dots have electron levels 130 meV below the bottom of the GaAs conduction band and heavy-hole levels at 90 meV above the top of the GaAs valence band. Combining with the photoluminescence results, the band structures of InAs and GaAs have been determined. (C) 2000 Elsevier Science B.V. All rights reserved.

Effect of In-mole-fraction in InGaAs overgrowth layer on self-assembled InAs/GaAs quantum dots

We have studied the optical and structural properties of InAs/GaAs QDs covered by InxGa1-xAs (0 less than or equal to x less than or equal to 0.3) layer using transmission electron microscopy, photoluminescence (PL) spectra and atomic force microscopy. We find that the strain reduces in the growth direction of InAs islands covered by InGaAs instead of GaAs layer. Significant redshift of PL peak energy and narrowing of PL linewidth are observed for the InAs QDs covered by 3 nm thick InGaAs layer. In addition, atomic force microscopy measurements indicate that the InGaAs islands will nucleate on top of InAs quantum dots, when 3 nm In0.3Ga0.7As overgrowth layer is deposited. This result can well explain the PL intensify degradation and linewidth increment of quantum dots with a higher In-mole-fraction InGaAs layer. The energy gap change of InAs QDs covered by InGaAs may be explained in terms of reducing strain, suppressing compositional mixing and increasing island height. (C) 2000 Elsevier Science B.V. All rights reserved.

The structural and photoluminescence properties of self-organized quantum dots in InAs/In0.53Ga0.47As multilayer on InP substrate

Self-organized InAs/In0.53Ga0.47As quantum dot (QD) multilayers were grown on InP substrate by molecular beam epitaxy. The structural and optical properties were characterized by using cross-sectional transmission electron microscopy (TEM) and photoluminescence (PL), respectively. Vertically aligned InAs quantum dots multilayer on InP substrate is demonstrated for the first time. Photoluminescence with a line width of similar to 26 meV was observed from the QDs multilayer. (C) 2000 Elsevier Science B.V. All rights reserved.

Optical properties of InAs self-organized quantum dots in n-i-p-i GaAs superlattices

The optical properties of InAs quantum dots in n-i-p-i GaAs superlattices are investigated by photoluminescence (PL) characterization. We have observed an anomalously large blueshift of the PL peak and increase of the PL linewidth with increasing excitation intensity, much smaller PL intensity decrease, and faster PL peak redshift with increasing temperature as compared to conventional InAs quantum dots embedded in intrinsic GaAs barriers. The observed phenomena can all be attributed to the filling effects of the spatially separated photogenerated carriers. (C) 2000 American Institute of Physics. [S0003-6951(00)03515-4].

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.

Strain effect on the band structure of InAs/GaAs quantum dots

The strain effect on the band structure of InAs/GaAs quantum dots has been investigated. 1 mu m thick InGaAs cap layer was added onto the InAs quantum dot layer to modify the strain in the quantum dots. The exciton energies of InAs quantum dots before and after the relaxation of the cap layer were determined by photoluminescence. When the epilayer was lifted off from the substrate by etching away the sacrifice layer (AlAs) by HF solution, the energy of exciton in the quantum dots decreases due to band gap narrowing resulted from the strain relaxation. This method can be used to obtain much longer emission wavelength from InAs quantum dots.