共查询到20条相似文献,搜索用时 31 毫秒
1.
L. Bouzaïene L. Sfaxi M. Baira H. Maaref C. Bru-Chevallier 《Journal of nanoparticle research》2011,13(1):257-262
Self-assembled InAs/GaAs (001) quantum dots (QDs) were grown by molecular beam epitaxy using ultra low-growth rate. A typical
dot diameter of around 28 ± 2 nm and a typical height of 5 ± 1 nm are observed based on atomic force microscopy image. The
photoluminescence (PL) spectra, their power and temperature dependences have been studied for ground (GS) and three excited
states (1–3ES) in InAs QDs. By changing the excitation power density, we can significantly influence the distribution of excitons
within the QD ensemble. The PL peak energy positions of GS and ES emissions bands depend on an excitation light power. With
increasing excitation power, the GS emission energy was red-shifted, while the 1–3ES emission energies were blue-shifted.
It is found that the full width at half maximum of the PL spectra has unusual relationship with increasing temperature from
9 to 300 K. The temperature dependence of QD PL spectra shown the existence of two stages of PL thermal quenching and two
distinct activation energies corresponding to the temperature ranges I (9–100 K) and II (100–300 K). 相似文献
2.
Epitaxially grown self-assembled InAs quantum dots (QDs) have found applications in optoelectronics. Efforts are being made
to obtain efficient quantum-dot lasers operating at longer telecommunication wavelengths, specifically 1.3 μm and 1.55 μm.
This requires narrow emission linewidth from the quantum dots at these wavelengths. In InAs/GaAs single layer quantum dot
(SQD) structure, higher InAs monolayer coverage for the QDs gives rise to larger dots emitting at longer wavelengths but results
in inhomogeneous dot-size distribution. The bilayer quantum dot (BQD) can be used as an alternative to SQDs, which can emit
at longer wavelengths (1.229 μm at 8 K) with significantly narrow linewidth (∼16.7 meV). Here, we compare the properties of
single layer and bilayer quantum dots grown with higher InAs monolayer coverage. In the BQD structure, only the top QD layer
is covered with increased (3.2 ML) InAs monolayer coverage. The emission line width of our BQD sample is found to be insensitive
towards post growth treatments. 相似文献
3.
V. Donchev E. S. Moskalenko K. F. Karlsson P. O. Holtz B. Monemar W. V. Schoenfeld J. M. Garcia P. M. Petroff 《Physics of the Solid State》2006,48(10):1993-1999
It is demonstrated that the microphotoluminescence (μPL) spectrum of a single InAs/GaAs self-assembled quantum dot (QD) undergoes
considerable changes when the primary laser excitation is complemented with an additional infrared laser. The primary laser,
tuned slightly below the GaAs band gap, provides electron-hole pairs in the wetting layer (WL), as well as excess free electrons
from ionized shallow acceptors in the GaAs barriers. An additional IR laser with a fixed energy well below the QD ground state
transition generates excess free holes from deep levels in GaAs. The excess electron and hole will experience diffusion separately,
due to the time separation between the two events of their generation, to eventually become captured into the QD. Although
the generation rates of excess carries are much lower than that of the electron-hole pair generation in the WL, they considerably
influence the QD emission at low temperatures. The integrated PL intensity increases by several times as compared to single-laser
excitation, and the QD exciton spectrum is redistributed in favor of a more neutral charge configuration. The dependence of
the observed phenomenon on the powers of the two lasers and the temperature has been studied and is consistent with the model
proposed. The concept of dual excitation could be successfully applied to different low-dimensional semiconductor structures
in order to manipulate their charge state and emission intensity.
The text was submitted by the authors in English. 相似文献
4.
K. Veselinov F. Grillot P. Miska E. Homeyer P. Caroff C. Platz J. Even X. Marie O. Dehaese S. Loualiche A. Ramdane 《Optical and Quantum Electronics》2006,38(4-6):369-379
Quantum dot (QD) lasers exhibit many interesting and useful properties such as low threshold current, temperature insensitivity
or chirpless behavior. In order to reach the standards of long-haul optical transmissions, 1.55 μm InAs QD lasers on InP substrate
have been developed. Based on time resolved photoluminescence (PL) measurements, carrier dynamics behavior is at first investigated.
Electroluminescence (EL) results are then shown at room temperature exhibiting a laser emission centered at 1.61 μm associated
to a threshold current density as low as 820 A/cm2 for a six InAs QD stacked layers. Finally, a rate equation model based on the reservoir theory is used to model both time-resolved
photoluminescence (TRPL) and electroluminescence results. It is shown that carrier dynamic calculations are in a good agreement
with measurements since the saturation effect occurring at high injected power is clearly predicted.
P. Miska: Previously at Laboratoire d’Etude des Nanostructures à Semiconducteurs. 相似文献
5.
W. Ouerghui A. Melliti M.A. Maaref J. Bloch 《Physica E: Low-dimensional Systems and Nanostructures》2005,28(4):519-524
We report systematic temperature-dependent measurements of photoluminescence spectra in self-assembled InGaAs/InAs/GaAs quantum dots (QDs). We have studied the rise in temperature of the ground-state homogeneous linewidth.A theoretical model is presented and accounts for the phonon-assisted broadening of this transition in individual QD. We have estimated the homogeneous linewidth of an individual QD from PL spectra of self-organized InAs/GaAs QDs by isolating the PL of each individual QD and fitting the narrow line associated with self-organized QDs through a Lorentzian convoluted by a Gaussian. We have observed a strong exciton–LO–phonon coupling (γLO) which becomes the dominating contribution to the linewidth above the temperature of 45 K. We have also derived the activation energy (ΔE) of the exciton–LO–phonon coupling, zero temperature linewidth (Γ0) and the exciton-LA-phonon coupling parameter (γAc). We report that our values are close to the values found in the literature for single InGaAs QD and InAs QD. 相似文献
6.
Lasers operating at 1.3 μm have attracted considerable attention owing to their potential to provide efficient light sources for next-generation high-speed communication systems. InAs/GaAs quantum dots (QDs) were pointed out as a reliable low-cost way to attain this goal. However, due to the lattice mismatch, the accumulation of strain by stacking the QDs can cause dislocations that significantly degrade the performance of the lasers. In order to reduce this strain, a promising method is the use of InAs QDs embedded in InGaAs layers. The capping of the QD layer with InGaAs is able to tune the emission toward longer and controllable wave-lengths between 1.1 and 1.5 μm. In this work, using the effective-mass envelope-function theory, we investigated theoretically the optical properties of coupled InAs/GaAs strained QDs based structures emitting around 1.33 μm. The calculation was performed by the resolution of the 3D Schrödinger equation. The energy levels of confined carriers and the optical transition energy have been investigated. The oscillator strengths of this transition have been studied with and without taking into account the strain effect in the calculations. The information derived from the present study shows that the InGaAs capping layer may have profound consequences as regards the performance of an InAs/GaAs QD based laser. Based on the present results, we hope that the present work make a contribution to experimental studies of InAs/GaAs QD based structures, namely the optoelectronic applications concerning infrared and mid-infrared spectral regions as well as the solar cells. 相似文献
7.
M. Bennour L. Bouza?ene F. Saidi L. Sfaxi H. Maaref 《Journal of nanoparticle research》2011,13(12):6527-6535
We have investigated the temperature dependence of photoluminescence (PL) peak position of InAs self-assembled quantum dots (QDs) grown on GaAs(11N)A (N = 3, 5) substrates. The interband transition energy is calculated by the resolution of the 3D Schrödinger equation for a parallelepipedic InAs QD, with a width of about 8 nm and a height around 3 nm. Experimentally, it was found that the PL spectra quenches at about 160 K. In addition, the full width at half maximum (FWHM) has an abnormal evolution with varying temperature. The latter effect maybe due to the carrier repopulation between QDs. The disorientation of the GaAs substrate and the low width of terraces which was presented in the high index surfaces have an important contribution in the PL spectra. Despite the non-realist chosen shape of QD and the simplest adopted model, theoretical and experimental results revealed a clear agreement. 相似文献
8.
M. Geddo R. Ferrini G. Guizzetti M. Patrini S. Franchi P. Frigeri G. Salviati L. Lazzarini 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(1):19-24
We report on a photoreflectance investigation in the 0.8-1.5 eV photon energy range and at temperatures from 80 to 300 K on
stacked layers of InAs/GaAs self-assembled quantum dots (QDs) grown by Atomic-Layer Molecular Beam Epitaxy. We observed clear
and well-resolved structures, which we attribute to the optical response of different QD families. The dependence of the ground
state transition energy on the number of stacked QD layers is investigated and discussed considering vertical coupling between
dots of the same column. It is shown that Coulomb interaction can account for the observed optical response of QD families
with different morphology coexisting in the same sample.
Received 17 November 1999 相似文献
9.
The microstructural and the optical properties of multiple closely stacked InAs/GaAs quantum dot (QD) arrays were investigated by using atomic force microscopy (AFM), transmission electron microscopy (TEM), and photoluminescence (PL) measurements. The AFM and the TEM images showed that high-quality vertically stacked InAs QD self-assembled arrays were embedded in the GaAs barriers. The PL peak position corresponding to the interband transitions from the ground electronic subband to the ground heavy-hole band (E1-HH1) of the InAs/GaAs QDs shifted to higher energy with increasing GaAs spacer thickness. The activation energy of the electrons confined in the InAs QDs increased with decreasing with GaAs spacer thickness due to the coupling effect. The present results can help to improve the understanding of the microstructural and the optical in multiple closely stafcked InAs/GaAs QD arrays. 相似文献
10.
F. Guffarth R. Heitz A. Schliwa K. Ptschke D. Bimberg 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):326
A pronounced modulation is observed in the photoluminescence (PL) spectrum of self-organized InAs/GaAs quantum dots (QDs), recorded at low excitation densities. The clearly distinguishable peaks are identified as a multimodal distribution of the ground state transition energy, originating from a discrete, stepwise variation of the structural properties of the QDs, which is associated with an increase of the QD height in monolayer (ML) steps. The observation of a ML splitting implies a flat QD shape with well-defined upper and lower interfaces as well as negligible indium segregation. The electronic properties of the InAs/GaAs QDs were investigated by PL and PL-excitation spectroscopy and are discussed based on realistic calculations for flat InAs/GaAs QDs with a truncated pyramidal shape based on an extended 8-band k·p model. The calculations predict a red shift of the ground state transition with each additional ML, which saturates for heights above 9 ML, is in good agreement with experiment. 相似文献
11.
《Physica E: Low-dimensional Systems and Nanostructures》2009,41(10):3160-3165
The influence of layer-by-layer temperature and substrate rotation on the optical property and uniformity of self-assembled InAs/In0.2Ga0.8As/GaAs quantum dots (QDs) gown with an As2 source was investigated. An improvement in the optical property of QDs was obtained by the precise control and optimization of growth temperature utilized for each layer, i.e., InAs QDs, InGaAs quantum wells, GaAs barriers and AlGaAs layers, respectively. By using a substrate rotation, the QD density increased from ∼1.4×1010 to ∼3.2×1010 cm−2 and its size also slightly increased, indicating a good quality of QDs. It is found that the use of an appropriate substrate rotation during growth improves the room-temperature (RT) optical property and uniformity of QDs across the wafer. For the QD sample with a substrate rotation of 6 rpm, the RT photoluminescence (PL) intensity is much higher and the standard deviation of RT-PL full-width at half-maximum is decreased by 35% compared to that grown without substrate rotation. 相似文献
12.
Light absorption by GaAs/AlAs heterostructures with a layer of self-assembled InAs quantum dots (QDs) at resonant tunneling
through an energy-selected QD has been investigated. A high sensitivity of the current through this selected tunneling channel
to the absorption of single photons with a wavelength λ ≲ 860 nm up to a temperature of 50 K is demonstrated; this sensitivity
is caused by the Coulomb effect of the photoexcited holes captured by surrounding QDs on the resonance conditions. It is shown
that single-photon absorption can discretely change the current through the system under study by a factor of more than 50.
The captured-hole lifetimes have been measured, and a model has been developed to qualitatively describe the experimental
data. It is also demonstrated that the InAs monolayer can effectively absorb photons. The properties of the heterostructure
studied can be used not only to detect photons but also to design logical valves and optical memory devices. 相似文献
13.
The intermixing of Sb and As atoms induced by rapid thermal annealing (RTA) was investigated for type II GaSb/GaAs self-assembled quantum dots (QD) formed by molecular beam epitaxy growth. Just as in InAs/GaAs QD systems, the intermixing induces a remarkable blueshift of the photoluminescence (PL) peak of QDs and reduces the inhomogeneous broadening of PL peaks for both QD ensemble and wetting layer (WL) as consequences of the weakening of quantum confinement. Contrary to InAs/GaAs QDs systems, however, the intermixing has led to a pronounced exponential increase in PL intensity for GaSb QDs with annealing temperature up to 875 °C. By analyzing the temperature dependence of PL for QDs annealed at 700, 750 and 800 °C, activation energies of PL quenching from QDs at high temperatures are 176.4, 146 and 73.9 meV. The decrease of QD activation energy with annealing temperatures indicates the reduction of hole localization energy in type II QDs due to the Sb/As intermixing. The activation energy for the WL PL was found to drastically decrease when annealed at 800 °C where the QD PL intensity surpassed WL. 相似文献
14.
The effect of temperature on the self-assembled InAs quantum dots (QDs) grown on GaAs substrate under arsenic shutter closed condition has been studied. From atomic force microscopy (AFM), it was found that the size of InAs dots exhibited a transition from single-sized uniformly distributed quantum dot (QD) at a growth temperature of 490°C to two groups of different sizes QDs at 510°C. Since the desorption rate of In atoms from the substrate surface is very high at 510°C, a growth model is proposed that attributes the larger sized QDs to the enhanced capture of desorbed In atoms by a local random protrusion which initiates a regenerative capture and growth process and leads to explosive growth. 相似文献
15.
Reflection high-energy electron diffraction, atomic force microscopy, transmission electron microscopy, and double-crystal X-ray curves showed that high-quality InAs quantum dot (QD) arrays inserted into GaAs barriers were embedded in an Al0.3Ga0.7As/GaAs heterostructure. The temperature-dependent photoluminescence (PL) spectra of the InAs/GaAs QDs showed that the exciton peak corresponding interband transition from the ground electronic subband to the ground heavy-hole subband (E1-HH1) was dominantly observed and that the peak position and the full width at half maximum corresponding to the interband transitions of the PL spectrum were dependent on the temperature. The activation energy of the electrons confined in the InAs/GaAs QDs was 115 meV. The electronic subband energy and the energy wave function of the Al0.3Ga0.7As/GaAs heterostructures were calculated by using a self-consistent method. The electronic subband energies in the InAs/GaAs QDs were calculated by using a three-dimensional spatial plane wave method, and the value of the calculated (E1-HH1) transition in the InAs/GaAs QDs was in reasonable agreement with that obtained from the PL measurement. 相似文献
16.
D.M. Schaadt S. Krauss R. Koch K.H. Ploog 《Applied Physics A: Materials Science & Processing》2006,83(2):267-269
We investigated the stress evolution during molecular-beam epitaxy of bilayer InAs/GaAs(001) quantum dot (QD) structures in
real time and with sub-monolayer precision using an in-situ cantilever beam setup. During growth of the InAs at 470 °C a stress
of 5.1 GPa develops in the wetting layer, in good agreement with the theoretical misfit stress. At a critical thickness of
1.5 monolayers the strain is relieved by the QD formation. In the case of InAs/GaAs bilayer structures, the second InAs layer
grows identical to the first for GaAs spacer thicknesses exceeding ∼13 nm. For thinner spacers the critical thickness for
the 2D/3D transition in the second layer decreases. The stress of the second InAs layer does not reach the value of the first,
indicating that InAs QDs grow on partially strained areas due to the strain field of the previous InAs layer.
PACS 68.35.-p; 68.35.Gy; 68.65.Hb; 81.07.Ta; 81.10.Aj 相似文献
17.
M. Inada I. Umezu P. O. Vaccaro S. Yamada A. Sugimura 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):317
We studied optical and electron transport properties of coupled InAs quantum dots (QDs) embedded in GaAs. Photoluminescence (PL) from the high dot density samples indicated asymmetry in the PL spectra when the ambient temperature is lower than about 50 K. Comparing this result with theoretical calculations, it is shown that this phenomenon is explained by the inter-dot electronic coupling effect. In the photo-conductance measurement, resonance peaks in the current–voltage characteristics were observed in the low-temperature region. The dependence of the resonance voltage on the magnetic field intensity was studied to extract the g-factor. It is also shown that the resonances are attributed to the current corresponding to the electron transport through QDs. According to these results, it is concluded that the inter-dot electronic coupling in the self-assembled InAs/GaAs QD systems occurs when the inter-dot spacing is as low as several nanometers and the ambient temperature is less than about 50 K. 相似文献
18.
《Superlattices and Microstructures》1999,25(1-2):97-104
We report on studies of excitation transfer processes in vertically self-organized pairs of unequal-sized quantum dots (QDs), created in InAs/GaAs bilayers having differing InAs deposition amounts in the first (seed) and subsequent layer. The former and latter enable independent control, respectively, of the density and the size distribution of the second layer QDs. This approach allows us to enhance the average volume and improve the uniformity of InAs QDs, resulting in low-temperature photoluminescence at 1.028 eV with a linewidth of 25 meV for 1.74 ML (seed)/3.00 ML InAs stacking. The optical properties of the formed pairs of unequal-sized QDs with clearly discernible ground-state transition energy depend on the spacer thickness and composition. Photoluminescence results provide evidence for nonresonant energy transfer from the smaller QDs in the seed layer to the larger QDs in the second layer in such asymmetric QD pairs. Transfer times down to 20 ps (36 ML GaAs spacer) are estimated, depending exponentially on the GaAs spacer thickness. 相似文献
19.
Zongyou Yin Xiaohong Tang Wei Liu Sentosa Deny Jinghua Zhao Daohua Zhang 《Journal of nanoparticle research》2007,9(5):877-884
InAs quantum dots (QDs) have been formed on GaAs (001) substrate by metal-organic vapor phase epitaxy (MOVPE) under the safer
growth conditions: using tertiarybutylarsine (TBA) to replace AsH3 as the arsenic source and replacing hydrogen by pure nitrogen as the carrier gas. Effects of growth conditions on the QD
formation have been investigated. It is observed that the wetting layer is stabilized with some material being transferred
to form the QDs due to the strain relaxation process during the QD formation. Dot size dispersion becomes broader when the
post-growth interruption is more than 20 s. Compared with normal one-step grown QDs, dot density increases greatly by 213%
after employing two-step deposition for QD growth. This is explained by considering the indium-flux-dependent nucleation density
at step 1 and kinetically self-limiting growth at step 2. The two photoluminescence (PL) emission peaks, 1.203 μm and 1.094 μm,
from the two-step grown QDs are attributed to E1–HH1 and E1–LH1 transitions of the QDs, respectively. The measured results agree well with those received by an 8 k·p theoretical calculation.
The narrow PL linewidth of ~50 nm shows high quality of the QDs. This paves the way to develop safer MOVPE process, using
TBA/N2 instead of AsH3/H2, to grow QDs for device application. 相似文献