Quantum-confined Stark effects of InAs/GaAs self-assembled quantum dot

Quantum-confined Stark effects in InAs/GaAs self-assembled quantum dots are investigated theoretically in the framework of effective-mass envelope function theory. The electron and hole energy levels and optical transition energies are calculated in the presence of perpendicular and parallel electric field. In our calculation, the effect of finite offset, valence band mixing, and strain are all taken into account. The results show that the perpendicular electric field weakly affects the electron ground state and hole energy levels. The energy levels are affected strongly by the parallel electric field. For the electron, the energy difference between the ground state and the first excited state decreases as electric field increases. The optical transition energies have clear redshifts in electric field. The theoretical results agree well with the available experimental data. Our calculated results are useful for the application of quantum dots to photoelectric devices. (C) 2000 American Institute of Physics. [S0021-8979(00)11001-7].

1.3μm InGaAs/InAs/GaAs Self-Assembled Quantum Dot Laser Diode Grown by Molecular Beam Epitaxy

The growth of multi-layer InGaAs/InAs/GaAs self-assembled quantum dots （QDs） by molecular beam epitaxy （MBE） is investigated,and a QD laser diode lasing at 1.33μm in continuous operation mode at room temperature is reported. The full width at half maximum of the band edge emitting peaks of the photoluminescence （PL） spectra at room temperature is less than 35meV for most of the multi-layer QD samples,revealing good,reproducible MBE growth conditions. Moreover,atomic force microscopy images show that the QD surface density can be controlled in the range from 1×10^10 to 7 ×10^10 cm^-2 . The best PL properties are obtained at a QD surface density of about 4×10^10cm^-2. Edge emitting lasers containing 3 and 5 stacked QD layers as the active layer lasing at room temperature in continuous wave operation mode are reported.

Single-photon emission at liquid nitrogen temperature from a single InAs/GaAs quantum dot

We report on the single photon emission from single InAs/GaAs self-assembled Stranski-Krastanow quantum dots up to 80K under pulsed and continuous wave excitations. At temperature 80 K, the second-order correlation function at zero time delay, g((2))(0), is measured to be 0.422 for pulsed excitation. At the same temperature under continuous wave excitation, the photon antibunching effect is observed. Thus, our experimental results demonstrate a promising potential application of self-assembled InAs/GaAs quantum dots in single photon emission at liquid nitrogen temperature.

Shape stability of InAs self-assembled islands on vicinal GaAs(001) substrates

We have grown InAs self-assembled islands on vicinal GaAs( 001) substrates. Atomic force microscopy and photoluminescence studies show that the islands have a clear bimodal size distribution. While most of the small islands whose growth is limited by the width of one multi-atomic step have compact symmetric shapes, a large fraction of the large islands limited by the width of one step plus one terrace have asymmetric shapes which are elongated along the multi-atomic step lines. These results can be attributed to the shape-related energy of the islands at different states of their growth. (C) 2008 Elsevier B. V. All rights reserved.

Size self-scaling effect in stacked InAs/InAlAs nanowire multilayers

Size self-scaling effect in stacked InAs/In0.52Al0.48As nanowires on InP substrates is revealed, i.e., the base width and height of the InAs nanowires have clear proportional dependence on thickness of the InAlAs spacer layer used in different samples. The photoluminescence wavelength from different samples, which varies between 1.3 and 1.9 mum, is also found closely correlated to the size self-scaling effect. This phenomenon can be well explained in the context of formation mechanism and growth features of the InAs/InAlAs nanowire arrays. The finding illustrates a degree of freedom to control the structural and optical properties of strained self-organized nanostructures. (C) 2004 American Institute of Physics.

InAs nanostructure grown with different growth rate in InAlAs matrix on InP (001) substrate

InAs self-organized nanostructures in In0.52Al0.48As matrix have been grown on InP (001) substrates by molecular beam epitaxy. The morphologies of the nanostructures are found to be strongly dependent on the growth rate of the InAs layer. By increasing the growth rate from 0.005 to 0.35 ML/s, the morphology of the nanostructure changes from wire to elongated dot and then changes back to wire again. Polarized photoluminescence of the InAs quantum wires and quantum dots are performed at 77 K, which are characterized by strong optical anisotropies. (C) 2003 Elsevier B.V. All rights reserved.

InAs/GaAs quantum-dot superluminescent diodes with 110 nm bandwidth

Broadband superluminescent diodes are fabricated by using InAs/GaAs self-assembled quantum dots as an active region. The devices exhibited properties of 110 run bandwidth with the centre of 1.1 mu m and above 30 mW output under pulse injection at room temperature.

A narrow photoluminescence linewidth of 19.2 meV at 1.35 mu m from In0.5Ga0.5As/GaAs quantum island structure grown by molecular beam epitaxy

A self-organized In0.5Ga0.5As/GaAs quantum island structure emitting at 1.35 mum at room temperature has been successfully fabricated by molecular beam epitaxy via cycled (InAs)(1)/GaAs)(1)monolayer deposition method. The photoluminescence measurement shows that a very narrow linewidth of 19.2 meV at 300 K has been reached for the first time, indicating effective suppression of inhomogeneous broadening of optical emission from the In0.5Ga0.5As island structure due to indium segregation reduction by introducing an AlAs layer and the strain reduction by inserting an In0.2Ga0.8As layer overgrown on the top of islands. The mound-like morphology of the islands elongated along the [1 (1) over bar0] azimuth are observed by the atomic force microscopy measurement, which reveals the fact that strain in the islands is partially relaxed along the [1 (1) over bar0] direction. Our results present important information for the fabrication of 1.3 mum wavelength quantum dot devices.

InAs self-assembled nanostructures grown on InP(001)

The 6-period stacked layers of self-assembled InAs quasi-quantum wires(qQWRs) and quantum dots(QDs) embedded into InAlAs on InP(001) substrates have been prepared by solid molecular beam epitaxy. The structures are characterized by atomic force microscopy(AFM) and transmission electron microscopy(TEM). From AFM we have observed for the first time that InAs qQWRs and QDs coexist, and we explained this phenomenon from the view of the energy related to the islands. Cross-sectional TEM shows that InAs qQWRs are vertically aligned every other layer along the growth direction [001], which disagrees with conventional vertical self-alignment of InAs QDs on GaAs substrate.

Size quantization effects in InAs self-assembled islands on InP(001) at the onset of 2D-to-3D transition

Photoluminescence spectroscopy has been used to investigate self-assembled InAs islands in InAlAs grown on InP(0 0 1) by molecular beam epitaxy, in correlation with transmission electron microscopy. The nominal deposition of 3.6 monolayers of InAs at 470 degrees C achieves the onset stage of coherent island formation. In addition to one strong emission around 0.74 eV, the sample displaces several emission peaks at 0.87, 0.92. 0.98, and 1.04 eV. Fully developed islands that coexist with semi-finished disk islands account for the multipeak emission. These results provide strong evidence of size quantization effects in InAs islands. (C) 1999 Elsevier Science B.V. All rights reserved.

Self-Heating Effect on the Two-State Lasing Behaviors in 1.3-mu m InAs-GaAs Quantum-Dot Lasers

Experimental and theoretical study of the self-heating effect on the two-state lasing behaviors in 1.3-mu m self-assembled InAs-GaAs quantum dot (QD) lasers is presented. Lasing spectra under different injected currents, light-current (L-I) curves measured in continuous and pulsed regimes as well as a rate-equation model considering the current heating have been employed to analyze the ground-state (GS) and excited-state (ES) lasing processes. We show that the self-heating causes the quenching of the GS lasing and the ES lasing by the increased carrier escape rate and the reduced maximum modal gain of GS and ES.

Interplay effects of temperature and injection power on photoluminescence of InAs/GaAs quantum dot with high and low areal density

In this report, we have investigated the temperature and injection power dependent photoluminescence in self-assembled InAs/GaAs quantum dots (QDs) systems with low and high areal density, respectively. It was found that, for the high-density samples, state filling effect and abnormal temperature dependence were interacting. In particular, the injection power-induced variations were most obvious at the temperature interval where carriers transfer from small quantum dots (SQDs) to large quantum dots (LQDs). Such interplay effects could be explained by carrier population of SQDs relative to LQDs, which could be fitted well using a thermal carrier rate equation model. On the other hand, for the low density sample, an abnormal broadening of full width at half maximum (FWHM) was observed at the 15-100 K interval. In addition, the FWHM also broadened with increasing injection power at the whole measured temperature interval. Such peculiarities of low density QDs could be attributed to the exciton dephasing processes, which is similar to the characteristic of a single quantum dot. The compared interplay effects of high-and low-density QDs reflect the difference between an interacting and isolated QDs system.

Investigation of gain recovery for InAs/GaAs quantum dot semiconductor optical amplifiers by rate equation simulation

The gain recoveries in quantum dot semiconductor optical amplifiers (QD SOAs) are numerically studied by rate equation simulation. Similar to the optical pump-probe experiment, the injection of double 150 fs optical pulses is used to simulate the gain recovery of a weak continuous signal under different injection levels, inhomogeneous broadenings, detuning wavelengths, and pulse signal energies for the QD SOAs. The obtained gain recoveries are then fitted by a response function with multiple exponential terms to determine the response times. The gain recovery can be described by three exponential terms with the time constants, which can be explained as carrier relaxation from the excited state to the ground state, carrier captured by the excited state from the wetting layer, and the supply of the wetting layer carriers. The fitted lifetimes decrease with the increase of the injection currents under gain unsaturation, slightly decrease with the decrease of inhomogeneous broadening of QDs, and increase with the increase of detuning wavelength between continuous signal and pulse signal and the increase of the pulse energy.

The fabrication and properties of InAs/GaAs columnal islands

A columnal islands system, which was composed of three layers of self-assembled InAs/GaAs quantum dots (QDs), has been fabricated by solid-source molecular beam epitaxy (MBE) through S-K mode on a (100) semi-insulating GaAs substrate. The effects of the thickness of GaAs space layer, the growth interruption time and the amount of InAs deposition on the emission wavelength of columnal islands were presented. The image of atomic force microscopy (AFM) indicated the columnal islands with high uniformity in size and shape. At room temperature, the emission wavelength of columnal islands with different effective heights was achieved 1.32 and 1.4 mum; however, the emission wavelength of single-layer QDs with normal height was just 1. l mum. It provides a useful and intuitive approach to artificially control the emission wavelength of a QD material system.

Changing planar thin film growth into self-assembled island formation by adjusting experimental conditions

Illustrated in this paper are two examples of altering planar growth into self-assembled island formation by adapting experimental conditions. Partial oxidation, undersaturated solution and high temperature change Frank-Van der Merwe (FM) growth of Al0.3Ga0.7As in liquid phase epitaxy (LPE) into isolated island deposition. Low growth speed, high temperature and in situ annealing in molecular beam epitaxy (MBE) cause the origination of InAs/GaAs quantum dots (QDs) to happen while the film is still below critical thickness in Stranski-Krastanow (SK) mode. Sample morphologies are characterized by scanning electron microscopy (SEM) or atomic force microscopy (AFM). It is suggested that such achievements are of value not only to fundamental researches but also to spheres of device applications as well. (c) 2004 Elsevier B.V. All rights reserved.