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1.
The carrier recombination dynamics in an ensemble of GaN/AlN quantum dots is studied. The model proposed for describing this dynamics takes into account the transition of carriers between quantum dots and defects in a matrix. Comparison of the experimental and calculated photoluminescence decay curves shows that the interaction between quantum dots and defects slows down photoluminescence decay in the ensemble of GaN/AlN quantum dots. 相似文献
2.
The mechanisms of temperature quenching of steady-state photoluminescence are studied for structures with hexagonal GaN quantum dots embedded in the AlN matrix. The structures are grown by molecular beam epitaxy. The study is conducted for structures with differently sized quantum dots, for which the peak of the photoluminescence band is in the range from 2.5 to 4.0 eV. It is found that the activation energy of thermal quenching of photoluminescence varies from 27 to 110 meV, as the quantum-dot height is decreased from 5 to 2 nm. A model is suggested to interpret the results. According to the model, the photo-luminescence signal is quenched because of the transfer of charge carriers from energy levels in the quantum dots to defect levels in the matrix. 相似文献
3.
G. I. Tselikov V. Yu. Timoshenko J. Plenge E. Rühl A. M. Shatalova G. A. Shandryuk A. S. Merekalov R. V. Tal’roze 《Semiconductors》2013,47(5):647-649
The photoluminescence properties of cadmium-selenide (CdSe) quantum dots with an average size of ~3 nm, embedded in a liquid-crystal polymer matrix are studied. It was found that an increase in the quantum-dot concentration results in modification of the intrinsic (exciton) photoluminescence spectrum in the range 500–600 nm and a nonmonotonic change in its intensity. Time-resolved measurements show the biexponential decay of the photoluminescence intensity with various ratios of fast and slow components depending on the quantum-dot concentration. In this case, the characteristic lifetimes of exciton photoluminescence are 5–10 and 35–50 ns for the fast and slow components, respectively, which is much shorter than the times for colloidal CdSe quantum dots of the same size. The observed features of the photoluminescence spectra and kinetics are explained by the effects of light reabsorption, energy transfer from quantum dots to the liquid-crystal polymer matrix, and the effect of the electronic states at the CdSe/(liquid crystal) interface. 相似文献
4.
The exciton spin alignment is measured in an ensemble of self-organized cubic GaN/AlN quantum dots. By picosecond time-resolved photoluminescence experiments, we show that the exciton linear polarization does not decay with time from 20 to 300 K. 相似文献
5.
The optical emission of non-polar GaN/AlN quantum dots has been investigated. The presence of stacking faults inside these quantum dots is evidenced in the dependence of the photoluminescence with temperature and excitation power. A theoretical model for the electronic structure and optical properties of non-polar quantum dots, taking into account their realistic shapes, is presented which predicts a substantial reduction of the internal electric field but a persisting quantum confined Stark effect, comparable to that of polar GaN/AlN quantum dots. Modeling the effect of a 3 monolayer stacking fault inside the quantum dot, which acts as zinc-blende inclusion into the wurtzite matrix, results in an additional 30% reduction of the internal electric field and gives a better account of the observed optical features. 相似文献
6.
The optical emission of non-polar GaN/AlN quantum dots has been investigated. The presence of stacking faults inside these quantum dots is evidenced in the dependence of the photoluminescence with temperature and excitation power. A theoretical model for the electronic structure and optical properties of non-polar quantum dots, taking into account their realistic shapes, is presented which predicts a substantial reduction of the internal electric field but a persisting quantum confined Stark effect, comparable to that of polar GaN/AlN quantum dots. Modeling the effect of a 3 monolayer stacking fault inside the quantum dot, which acts as zinc-blende inclusion into the wurtzite matrix, results in an additional 30% reduction of the internal electric field and gives a better account of the observed optical features. 相似文献
7.
We report the characteristics of ternary InAlP and InGaP self-assembled quantum dots grown by metalorganic chemical vapor
deposition. The structural and optical properties of these ternary quantum dots are compared with the characteristics of binary
InP quantum dots grown under similar conditions. Because these ternary quantum dots have different bandgaps, strain, and composition
compared to binary InP quantum dots, the ternary quantum-dot optical and physical properties are markedly different. The quantum-dot
structures are grown uncapped (exposed QDs) and capped (embedded QDs) and characterized by atomic force microscopy (AFM) and
photoluminescence (PL). InAlP quantum dots have higher densities and smaller sizes and InGaP quantum dots have smaller densities,
as compared with InP quantum dots grown under similar conditions. Also, a random and broad size distribution is observed for
InGaP quantum dots and the luminescence from InGaP dots is broader than for InP quantum dots. 相似文献
8.
GaN-based structures with InGaN quantum dots in the active region emitting in the near-ultraviolet region are studied. In this study, two types of structures, namely, with InGaN quantum dots in a GaN or AlGaN matrix, are compared. Photoluminescence spectra are obtained for both types of structures in a temperature range of 80–300 K and at various pumping densities, and electroluminescence spectra are obtained for light-emitting (LED) structures with various types of active region. It is shown that the structures with quantum dots in the AlGaN matrix are more stable thermally due to the larger localization energy compared with quantum dots in the GaN matrix. Due to this, the LED structures with quantum dots in an AlGaN matrix are more effective. 相似文献
9.
《Microelectronics Journal》1999,30(4-5):353-356
We observe in strained GaN self-assembled quantum dots grown on an AlN layer, a dramatic modification of the optical emission spectra as the dot size varies. In “large” quantum dots with an average height of 4.1 nm, the photoluminescence (PL) peak is centered at 2.95 eV, nearly 0.5 eV below the bulk GaN bandgap. We attribute this enormous redshift to a giant 5.5 MV cm−1 piezoelectric field present in our dots. Temperature-dependent PL studies reveal the strongly zero-dimensional character of this QD system and are consistent with an intrinsic PL mechanism. 相似文献
10.
G. G. Tarasov Z. Ya. Zhuchenko M. P. Lisitsa Yu. I. Mazur Zh. M. Wang G. J. Salamo T. Warming D. Bimberg H. Kissel 《Semiconductors》2006,40(1):79-83
Self-assembled quantum dots (QDs) in double-layer InAs/GaAs structures are studied by resonant photoluminescence and photoluminescence excitation spectroscopy. A weakly correlated (50%) double-layer system with an array of vertically coupled QDs (asymmetric quantum-dot molecules) was formed in a structure consisting of the 1.8-monolayer-thick first and the 2.4-monolayer-thick second InAs layers separated by 50 monolayers of GaAs. The nature of discrete quantum states in this system was studied and resonances corresponding to vertically coupled QDs were clearly observed for the first time. 相似文献
11.
A. N. Kosarev V. V. Chaldyshev V. V. Preobrazhenskii M. A. Putyato B. R. Semyagin 《Semiconductors》2016,50(11):1499-1505
The photoluminescence of InAs semiconductor quantum dots overgrown by GaAs in the low-temperature mode (LT-GaAs) using various spacer layers or without them is studied. Spacer layers are thin GaAs or AlAs layers grown at temperatures normal for molecular-beam epitaxy (MBE). Direct overgrowth leads to photoluminescence disappearance. When using a thin GaAs spacer layer, the photoluminescence from InAs quantum dots is partially recovered; however, its intensity appears lower by two orders of magnitude than in the reference sample in which the quantum-dot array is overgrown at normal temperature. The use of wider-gap AlAs as a spacer-layer material leads to the enhancement of photoluminescence from InAs quantum dots, but it is still more than ten times lower than that of reference-sample emission. A model taking into account carrier generation by light, diffusion and tunneling from quantum dots to the LT-GaAs layer is constructed. 相似文献
12.
Spontaneous and piezoelectric polarization in hexagonal GaN/AlGaN heterostructures give rise to large built-in electric fields.
The effect of the builtin electric field in GaN/AlxGa1−xN quantum wells was investigated for x=0.2 to 0.8 by photoluminescence studies. The quantum well structures were grown by
molecular beam epitaxy on (0001) sapphire substrates. Cross-sectional transmission electron microscopy performed on the samples
revealed abrupt interfaces and uniform layer thicknesses. The low temperature (4 K) photoluminescence peaks were progressively
red-shifted due to the quantum confined Stark effect depending on the AlN mole fraction in the barriers and the thickness
of the GaN quantum well. Our results verify the existence of very large built-in electric fields of up to 5 MV/cm in GaN/Al0.8Ga0.2N quantum wells. 相似文献
13.
A. F. Tsatsul’nikov A. Yu. Egorov A. E. Zhukov A. R. Kovsh V. M. Ustinov N. N. Ledentsov M. V. Maksimov B. V. Volovik A. A. Suvorova N. A. Bert P. S. Kop’ev 《Semiconductors》1997,31(7):722-725
The modification produced in the structural and optical properties of vertically coupled In0.5Ga0.5As quantum dots in a GaAs matrix by increasing the number of deposited layers of quantum dots has been investigated. It was
shown that the deposition of a sequence of In0.5Ga0.5As quantum-dot planes separated by narrow (of the order of the height of the quantum dots) GaAs layers gives rise to an interaction
between neighboring vertically coupled quantum dots. This interaction shifts the photoluminescence line due to the recombination
of nonequilibrium carriers via states of the quantum dots into the region of lower photon energies.
Fiz. Tekh. Poluprovodn. 31, 851–854 (July 1997) 相似文献
14.
Grandjean N. Ilegems M. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》2007,95(9):1853-1865
General properties of III-V nitride-based quantum dots (QDs) are presented, with a special emphasis on InGaN/GaN QDs for visible optoelectronic devices. Stranski-Krastanov GaN/AlN dots are first discussed as a prototypical system. It is shown that the optical transition energies are governed by a giant quantum-confined Stark effect, which is the consequence of the presence of a large built-in internal electric field of several MV/cm. Then we move to InGaN/GaN QDs, reviewing the different fabrication approaches and their main optical properties. In particular, we focus on InGaN dots that are formed spontaneously by In composition fluctuations in InGaN quantum wells. Finally, some advantages and limitations of nitride laser diodes with active regions based on InGaN QDs are discussed, pointing out the requirements on dot uniformity and density in order to be able to exploit the expected quantum confinement effects in future devices. 相似文献
15.
D. S. Abramkin K. S. Zhuravlev T. S. Shamirzaev A. V. Nenashev A. K. Kalagin 《Semiconductors》2011,45(2):179-187
The problem of how the probability of trapping of charge carriers into quantum dots via the wetting layer influences the steady-state
and time-dependent luminescence of the wetting layer and quantum dots excited via the matrix is analyzed in the context of
some simple models. It is shown that the increase in the integrated steady-state luminescence intensity of quantum dots with
increasing area fraction occupied by the quantum dots in the structure is indicative of the suppression of trapping of charge
carriers from the wetting layer into the quantum dots. The same conclusion follows from the independent decays of the time-dependent
luminescence signals from the wetting layer and quantum dots. The processes of trapping of charge carriers into the InAs quantum
dots in the AlAs matrix at 5 K are studied experimentally by exploring the steady-state and time-dependent photoluminescence.
A series of structures with different densities of quantum dots has been grown by molecular-beam epitaxy on a semi-insulating
GaAs (001) substrate. It is found that the integrated photoluminescence intensity of quantum dots almost linearly increases
with increasing area occupied with the quantum dots in the structure. It is also found that, after pulsed excitation, the
photoluminescence intensity of the wetting layer decays more slowly than the photoluminescence intensity of the quantum dots.
According to the analysis, these experimental observations suggest that trapping of excitons from the wetting layer into the
InAs/AlAs quantum dots at 5 K is suppressed. 相似文献
16.
The importance of fully coupled and semi-coupled piezoelectric models for quantum dots are compared. Differences in the strain of around 30% and in the electron energies of up to 30 meV were found possible for GaN/AlN dots. 相似文献
17.
V. G. Talalaev J. W. Tomm N. D. Zakharov P. Werner B. V. Novikov G. É. Cirlin Yu. B. Samsonenko A. A. Tonkikh V. A. Egorov N. K. Polyakov V. M. Ustinov 《Semiconductors》2004,38(6):696-701
Tunnel-coupled pairs of InAs quantum dots (quantum molecules) were formed by molecular beam epitaxy in a GaAs matrix. Optical and structural properties of the obtained quantum molecules were studied. Four molecular exciton states forming a photoluminescence spectrum were revealed. The photoluminescence decay times indicate the possibility of interlevel radiative recombination from the second excited state, which is of particular importance for designing mid-infrared devices. 相似文献
18.
N. S. Volkova A. P. Gorshkov A. V. Zdoroveishchev O. V. Vikhrova B. N. Zvonkov 《Semiconductors》2013,47(12):1583-1586
The effect of the incorporation of an InGaAs quantum well into structures with InAs/GaAs quantum dots grown by gas-phase epitaxy on their optoelectronic properties is analyzed in the mode with increased growth-interruption time. It is established that the quantum-dot energy spectrum is weakly sensitive to variations in the thickness and composition of the double InGaAs/GaAs coating layer. The deposition of a quantum well onto a layer of quantum dots decreases the emission-barrier effective height in them. The conditions under which the quantum well can be used for protecting the quantum-dot active layer against penetration by defects generated during structure-surface anodic oxidation are determined. 相似文献
19.
The effect of doping with copper on the photoluminescence properties of cadmium selenide quantum dots 4 nm in dimension is
studied. The quenching of the excitonic photoluminescence band related to the quantum dots and the appearance of an impurity
photoluminescence band in the near-infrared region are observed after doping of the quantum dots with copper. It is established
that, on doping of the quantum dots, the photoluminescence kinetics undergoes substantial changes. The photoluminescence kinetics
of the undoped quantum dots is adequately described by a sum of exponential relaxation relations, whereas the photoluminescence
kinetics experimentally observed in the region of the impurity band of the copper-doped samples follows stretched exponential
decay, with the average lifetimes 0.3–0.6 μs at the photon energies in the range of 1.47–1.82 eV. The experimentally observed
changes in the photoluminescence properties are attributed to transformation of radiative centers in the quantum dots when
doped with copper atoms. 相似文献
20.
Ya. V. Terent’ev A. A. Toropov B. Ya. Meltser A. N. Semenov V. A. Solov’ev I. V. Sedova A. A. Usikova S. V. Ivanov 《Semiconductors》2010,44(2):194-197
GaAs/GaSb type-II quantum-dot heterostructures were grown by molecular-beam epitaxy. The circularly polarized photoluminescence
of these samples in a magnetic field up to 4.7 T in the Faraday configuration was investigated. It was found that the emission
from quantum dots in a magnetic field is σ−-polarized, which corresponds to the electron-spin component along the magnetic-field vector of +1/2. The degree of polarization
increases with increasing excitation intensity. The observed effect is explained in terms of spin injection from the GaSb
matrix, where spin orientation appears owing to the Zeeman splitting of the conduction band. An increase in the degree of
polarization occurs due to a reduction in the charge-carrier radiative lifetime in type-II quantum dots with increasing excitation
level. 相似文献