共查询到20条相似文献,搜索用时 62 毫秒
1.
V. G. Talalaev B. V. Novikov A. S. Sokolov I. V. Strom J. W. Tomm N. D. Zakharov P. Werner G. E. Cirlin A. A. Tonkikh 《Semiconductors》2007,41(2):197-204
Photoluminescence of multilayer structures with InAs quantum dots grown in the p-n junction in GaAs by molecular-beam epitaxy is studied. Formation of vertical columns of quantum dots is verified by the data of transmission electron microscopy. It is shown that a natural increase in the size of quantum dots from layer to layer brings about their vertical coalescence at the upper part of a column. An unbalance of electronic levels caused by the enlargement of quantum dots was compensated by an external electric field, so that the resonance of ground electronic states in the column was attained. The onset of resonances was checked by the methods of steady-state and time-resolved photoluminescence. It is shown that, in the case of a resonance, the photoluminescence intensity and the radiative lifetime of excitons increase (up to 0.6–2 ns), while the time of tunneling of charge carriers becomes shorter (shorter than 150 ps). Outside the resonances, tunneling of electrons is appreciably enhanced owing to the involvement of longitudinal optical phonons. If only these phonons are involved, the time of nonresonance tunneling between quantum dots becomes shorter than the time of relaxation of charge carriers from the barrier (100 and 140 ps, respectively). 相似文献
2.
The photoluminescence spectra of CdS quantum dots grown in a borosilicate glass by sol-gel technology are recorded and analyzed. It is shown that the photoluminescence spectra of the samples are related to annihilation of free (interior) excitons in the ground state and excited state. Emission associated with the surface states of the quantum dots is detected in the region around 2.7 eV for the first time. The emission is due to recombination of electrons localized at the surface with heavy holes in the free states of the quantum dots. Resonance excitation of the structures makes it possible to reveal the specific features of the localized surface states responsible for the photoluminescence band. The properties of the band are, to a large extent, similar to the properties of the emission bands of both three-dimensional media (amorphous semiconductors and substitution alloys) and two-dimensional systems (quantum wells and superlattices). 相似文献
3.
4.
Fiore A. Oesterle U. Stanley R.P. Houdre R. Lelarge F. Ilegems M. Borri P. Langbein W. Birkedal D. Hvam J.M. Cantoni M. Bobard F. 《Quantum Electronics, IEEE Journal of》2001,37(8):1050-1058
We present a comprehensive study of the structural and emission properties of self-assembled InAs quantum dots emitting at 1.3 μm. The dots are grown by molecular beam epitaxy on gallium arsenide substrates. Room-temperature emission at 1.3 μm is obtained by embedding the dots in an InGaAs layer. Depending on the growth structure, dot densities of 1-6×1010 cm-2 are obtained. High dot densities are associated with large inhomogeneous broadenings, while narrow photoluminescence (PL) linewidths are obtained in low-density samples. From time-resolved PL experiments, a long carrier lifetime of ≈1.8 ns is measured at room temperature, which confirms the excellent structural quality. A fast PL rise (τrise=10±2 ps) is observed at all temperatures, indicating the potential for high-speed modulation. High-efficiency light-emitting diodes (LEDs) based on these dots are demonstrated, with external quantum efficiency of 1% at room temperature. This corresponds to an estimated 13% radiative efficiency. Electroluminescence spectra under high injection allow us to determine the transition energies of excited states in the dots and bidimensional states in the adjacent InGaAs quantum well 相似文献
5.
A. I. Khrebtov V. G. Talalaev P. Werner V. V. Danilov M. V. Artemyev B. V. Novikov I. V. Shtrom A. S. Panfutova G. E. Cirlin 《Semiconductors》2013,47(10):1346-1350
The possibility of fabricating a composite system based on colloidal CdSe/ZnS quantum dots and GaAs nanowires is demonstrated and the structural and emission properties of this system are investigated by electron microscopy and photoluminescence spectroscopy techniques. The good wettability and developed surface of the nanowire array lead to an increase in the surface density of quantum dots and, as a consequence, in the luminosity of the system in the 600-nm wavelength region. The photoluminescence spectrum of the quantum dots exhibits good temperature stability in the entire range 10–295 K. The impact of surface states on energy relaxation and the role of exciton states in radiative recombination in the quantum dots are discussed. 相似文献
6.
Hong-Wen Ren Selvakumar V. Nair Jeong-Sik Lee Shigeo Sugou Yasuaki Matsumoto 《Journal of Electronic Materials》2000,29(5):520-524
Coupled quantum dot-pairs were fabricated by growing InP self-assembled islands as stressors on InGaAs/GaAs double quantum
wells. State filling in the photoluminescence spectra was used to resolve the quantum states in the coupled dots. The total
strain field below the stressor decays exponentially with a penetration depth of about 25 nm, within which a dot-pair can
be fabricated. Strong coupling is observed at a barrier width less than 4 nm separating the dot-pair. By increasing the indium
composition in the lower well in order to match its dot level with one in the upper dot with identical quantum numbers, resonant
coupling between the electron states with identical quantum numbers in the two dots can be achieved. Decoupling of the hole
states and exchange of the electron bonding states from dominating the upper dot to the lower one are clearly resolved from
the state energies and their spacings. 相似文献
7.
The results of studies of samples containing ZnSe quantum dots with a density corresponding to or considerably higher than
the exciton percolation threshold, at which quantum dots form conglomerates, are reported. Excitonic emission from a percolation
cluster of bound quantum dots as a fractal object is observed for the first time. Analysis of the structure of the photoluminescence
spectra shows that the spectra are determined by the contribution of exciton states that belong to different structural elements
of the percolation cluster, specifically, to the skeleton (backbone), dangling (dead) ends, and internal hollow spaces. A
qualitative model is proposed to interpret the dependence of the exciton energy in these structural elements on the concentration
of quantum dots in the material. 相似文献
8.
在该研究中,通过激光全息和湿法腐蚀的方法在InAs/GaAs量子点材料上制备光子晶体,研究了由激光二极管激发制备了光子晶体的InAs / GaAs量子点材料的光致发光光谱.发现具有光子晶体的量子点材料的光谱显示出多峰结构,光子晶体对短波长部分的发光增强和调制比对长波长部分的增强和调制更明显.InAs / GaAs量子点的光致发光光谱通过刻蚀形成的光子晶体结构得到了调控,并且量子点的激发态发光得到了明显增强. 相似文献
9.
测量了自组织多层In0.55Al0.45As/Al0.5Ga0.5As量子点的变温光致发光谱,同时观察到来自浸润层和量子点的发光,首次直接观察到了浸润层和量子点之间的载流子热转移.分析发光强度随温度的变化发现浸润层发光的热淬灭包括两个过程:低温时浸润层的激子从局域态热激发到扩展态,然后被量子点俘获;而温度较高时则通过势垒层的X能谷淬灭.利用速率方程模拟了激子在浸润层和量子点间的转移过程,计算结果与实验符合得很好 相似文献
10.
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
11.
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
12.
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
13.
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
14.
K. V. Maremyanin D. I. Kryzhkov S. V. Morozov S. M. Sergeev D. I. Kuritsyn D. M. Gaponova V. Ya. Aleshkin Yu. G. Sadof’ev 《Semiconductors》2014,48(11):1463-1466
The time-resolved photoluminescence of GaAs/AlGaAs quantum-cascade structures under intense pulse excitation is studied. Aside from optical transitions between the ground electron and hole states of a system of two tunnel-coupled quantum wells, the photoluminescence spectrum at short times after the excitation pulse exhibits features corresponding to transitions between the excited states of these wells, which are not observed in time-integrated photoluminescence spectra. It is shown that, due to a high pump level, the electron gas is initially strongly heated, which makes it possible to observe band-to-band transitions between both the ground and excited states. Nonequilibrium carriers cool down with a characteristic relaxation time of ~125 ps. 相似文献
15.
Temperature dependent photoluminescence and cathodoluminescence of selfassembled CdSe/ZnSe quantum dots grown by metalorganic
vapor phase deposition were investigated. We found an unusual large red shift and a narrowing of the photoluminescence peak
with temperature increases. Cathodoluminescence studies of a small number of quantum dots showed that the broad peak observed
in the photoluminescence spectra is, in fact, made up of a series of narrower peaks, coming from quantum dots of different
sizes. While the intensity of luminescence from small dots drops monotonously with temperature rises, that from the large
dots displays a peculiar behavior. It actually increases within the temperature range of 140–170 K, the same range in which
the photoluminescence peak shows narrowing. The simultaneous increase of luminescence from some quantum dots and decrease
from others are believed to be responsible for the red shift and narrowing of the observed photoluminescence peak. A simple
analytically solvable rate equation model was used to understand the spectral data. We suggest that the unusual behaviors
observed can be understood as resulting from a transfer of thermally activated carriers from small to large quantum dots. 相似文献
16.
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
17.
N. V. Sibirev V. G. Talalaev A. A. Tonkikh G. E. Cirlin V. G. Dubrovskiĭ N. D. Zakharov P. Werner 《Semiconductors》2006,40(2):224-228
The energy band diagram of the multilayered Ge0.8Si0.2/Ge0.1Si0.9 heterostructures with vertically correlated quantum dots is analyzed theoretically. With regard to fluctuations of the thickness layer in the columns of quantum dots and to the exciton-phonon coupling, it is shown that the electron states constitute a miniband. The hole wave functions remain localized in the quantum dots. The spectrum of optical transitions calculated for a 20-layered structure at room temperature is in good agreement with the experimental photoluminescence spectrum that involves an intense band at about 1.6 μm. From theoretical considerations and experimental measurements, specific evidence for the miniband in the superlattice is deduced; it is found that the overlap integrals of the wave functions of electrons and holes and the integrated intensity of the photoluminescence band of the Ge quantum dots are described by quadratic functions of the number of the structure periods. 相似文献
18.
A. S. Shkolnik A. V. Savelyev L. Ya. Karachinsky N. Yu. Gordeev R. P. Seisyan G. G. Zegrya S. Pellegrini G. S. Buller V. P. Evtikhiev 《Semiconductors》2008,42(3):291-297
The results of time-resolved photoluminescence studies of heterostructures containing monolayer arrays of InAs/GaAs quantum dots are presented. A two-component time dependence of intensity of photoluminescence from the ground state of quantum dots, with characteristic times of the slow component up to hundreds of nanoseconds and those of rapid one several nanoseconds, is studied. It is shown that the slow component is determined by the transport of nonequilibrium charge carriers between the quantum dots. At low temperatures, the time of the slow component is determined by tunneling, and at high temperatures by thermal escape of nonequilibrium charge carriers. The ratio of the contributions of tunneling and thermal escape is determined by the degree of isolation of quantum dots. A theoretical model is constructed that describes the effect of the dynamics of carrier transport on the emergence and decay of the slow component of photoluminescence. 相似文献
19.
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
20.
C. E. Stutz Qianghua Xie R. L. Jones J. L. Brown 《Journal of Electronic Materials》2000,29(11):L29-L31
The accumulation of charge in InGaAs quantum dots has been measured at room temperature by the photoelectrochemical capacitance-voltage
(CV) technique for the first time. A carrier per quantum dot ratio greater than four has been observed. The use of atomic
force microscopy and low temperature and room temperature photoluminescence (PL) confirm the existence of quantum dots. Also,
a possible excited state is indicated by room temperature PL in a sample with small quantum dots. 相似文献