共查询到20条相似文献,搜索用时 15 毫秒
1.
T. Nakaoka S. Kako Y. Arakawa 《Physica E: Low-dimensional Systems and Nanostructures》2006,32(1-2):148
We have experimentally and theoretically investigated quantum confined Stark effect in hexagonal self-assembled GaN/AlN quantum dots. We have observed a blueshift of up to 100 meV for vertical electric field applied against the built-in electric field while we have observed a redshift for the electric field along the built-in field. The experimental result is compared with a charge self-consistent effective mass calculation, taking into account strain, piezoelectric charge, and pyroelectric charge. The tunability of the emission energy and the exciton binding energy is discussed. 相似文献
2.
Mechanisms of the generation and the radiative and nonradiative recombination of carriers in structures with GaN quantum dots in the AlN matrix are studied experimentally and theoretically. Absorption, stationary and nonstationary photoluminescence of quantum dots at different temperatures are investigated. It is found that the photoluminescence intensity considerably decreases with the temperature while the photoluminescence kinetics weakly depends on the temperature. The photoluminescence kinetics is shown to be determined by radiative recombination inside quantum dots. A mechanism of nonradiative recombination is proposed, according to which the main reason for the thermal quenching of photoluminescence is nonradiative recombination of charge carriers, generated by optical transitions between quantum dots and wetting layer states. 相似文献
3.
B. Daudin C. Adelmann N. Gogneau E. Sarigiannidou E. Monroy F. Fossard J. L. Rouvire 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):540
The conditions to grow GaN quantum dots (QDs) by plasma-assisted molecular beam epitaxy will be examined. It will be shown that, depending on the Ga/N ratio value, the growth mode of GaN deposited on AlN can be either of the Stranski–Krastanow (SK) or of the Frank–Van der Merwe type. Accordingly, quantum wells or QDs can be grown, depending on the desired application. In the particular case of modified SK growth mode, it will be shown that both plastic and elastic strain relaxation can coexist. Growth of GaN QDs with N-polarity will also be discussed and compared to their counterpart with Ga polarity. 相似文献
4.
5.
In this work, a numerical approach to investigate the room temperature luminescence emission from core/shell nanowire is presented where GaN quantum discs (QDiscs), periodically distributed in AlxGa1−xN nanowire, is considered as core and AlxGa1−xN as shell. Thin disc shaped (Ring shaped) n-doped region has been placed at the GaN/ AlxGa1−xN (AlxGa1−xN /air) interface in AlxGa1−xN region in axial (radial) directions. To obtain energy levels and related wavefunctions, self-consistent procedure has been employed to solve Schrodinger-Poisson equations with considering the spontaneous and piezoelectric polarization. Then luminescence spectrum is studied in details to recognize the parameters influent in luminescence. The results show that the amount of doping, size of QDiscs and theirs numbers have remarkable effects on the band to band luminescence emission. Our numerical calculations gives some insights into the luminescence emission of core/shell nanowire and exhibits a useful tool to analyze findings in experiments. 相似文献
6.
M.A. Migliorato D. Powell E.A. Zibik L.R. Wilson M. Fearn J.H. Jefferson M.J. Steer M. Hopkinson A.G. Cullis 《Physica E: Low-dimensional Systems and Nanostructures》2005,26(1-4):436
Atomistic simulations that use the Tersoff empirical potential accurately reproduce the effects of the presence of compositional disorder in strained semiconductor alloys. This method is applied to InGaAs quantum dot islands, for which gradients in the In composition distribution have been observed and accurately measured, and we demonstrate that the internal piezoelectric fields contribute strongly to the nature of the electron wavefunctions. The theoretical predictions are supported by experimental evidence: intersubband absorption measurements confirm that the p-states degeneracy for the electron first excited state is lifted and a minimum splitting of at least 5 meV is to be generally expected. 相似文献
7.
D. P. Williams A. D. Andreev D. A. Faux E. P. O'Reilly 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):358
We present a simple analytical approach to calculate the built-in strain-induced and spontaneous piezoelectric fields in nitride-based quantum dots (QDs) and then apply the method to describe the variation of exciton, biexciton and charged exciton energy with dot size in GaN/AlN QDs. We first present the piezoelectric potential in terms of a surface integral over the QD surface, and confirm that, due to the strong built-in electric field, the electrons are localised near the QD top and the holes are localised in the wetting layer just below the dot. The strong localisation and smaller dielectric constant results in much larger Coulomb interactions in GaN/AlN QDs than in typical InAs/GaAs QDs, with the interaction between two electrons, Jee, or two holes, Jhh, being about a factor of three larger. The electron–hole recombination energy is always blue shifted in the charged excitons, X− and X+, and the biexciton, and the blue shift increases with increasing dot height. We conclude that spectroscopic studies of the excitonic complexes should provide a useful probe of the structural and piezoelectric properties of GaN-based QDs. 相似文献
8.
The energy levels of zinc-blende GaN quantum dots (QDs) are studied within the framework of the effective-mass envelope-function approximation. The dependence of the energy of electron and hole states on the quantum dot (QD) size is presented. The selection rules for optical transitions are given and the oscillator strengths of the dipole-allowed transitions for various QD radii are calculated with the wavefunctions of quantized energy levels. The theoretical absorption spectrum of GaN QDs is in good agreement with the existing experimental result. 相似文献
9.
Qingwen Deng Xiaoliang Wang Cuibai Yang Hongling Xiao Cuimei Wang Haibo Yin Qifeng HouJinmin Li Zhanguo WangXun Hou 《Physica B: Condensed Matter》2011,406(1):73-76
In this work, the structure of InxGa1−xN/GaN quantum dots solar cell is investigated by solving the Schrödinger equation in light of the Kronig-Penney model. Compared to p-n homojunction and heterojunction solar cells, the InxGa1−xN/GaN quantum dots intermediate band solar cell manifests much larger power conversion efficiency. Furthermore, the power conversion efficiency of quantum dot intermediate band solar cell strongly depends on the size, interdot distance and gallium content of the quantum dot arrays. Particularly, power conversion efficiency is preferable with the location of intermediate band in the middle of the potential well. 相似文献
10.
Konrad Bellmann Farsane Tabataba‐Vakili Tim Wernicke Andre Strittmatter Gordon Callsen Axel Hoffmann Michael Kneissl 《固体物理学:研究快报》2015,9(9):526-529
GaN quantum dots (QDs) are realized on (0001) AlN templates by growing a thin GaN layer on an AlN buffer layer and applying a subsequent desorption step without ammonia present. A growth interruption (GRI), which is commonly applied after the GaN growth allowing for QD formation, is systematically investigated regarding the temperature, duration and initial GaN coverage. Without GRI the initial GaN layer exhibits a two‐dimensional nonuniform growth at the step edges. In this study, the surface morphology only changes significantly if the GRI is performed without ammonia exposure. Thus, an initial two‐dimensional GaN layer can be shaped into three‐dimensional nanostructures. Presented coverage studies by atomic force microscopy (AFM) show desorption as the main driving force for island evolution. By tailoring the growth parameters, GaN QDs can be achieved. Uncapped GaN samples exhibit QDs with 1.2 nm in height and 30 nm in diameter. Additionally, capped GaN QDs exhibit excitonic luminescence lines at about 4.3 eV with FWHM down to 2 meV and an excitonic fine structure splitting of 7 meV. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
11.
12.
L. Doyennette A. Vardi F. Guillot L. Nevou M. Tchernycheva A. Lupu R. Colombelli G. Bahir E. Monroy F.H. Julien 《Superlattices and Microstructures》2006,40(4-6):262
We have demonstrated GaN/AlN quantum dots (QD) photodetectors, relying on intraband absorption and in-plane carrier transport in the wetting layer. The devices operate at room temperature in the wavelength range 1.3–1.5 μm. Samples with 20 periods of Si-doped GaN QD layers, separated by 3 nm-thick AlN barriers, have been grown by plasma-assisted molecular-beam epitaxy on an AlN buffer on a c-sapphire substrate. Self-organized dots are formed by the deposition of 5 monolayers of GaN under nitrogen-rich conditions. The dot height is 1.2±0.6 to 1.3±0.6 nm and the dot density is in the range 1011–1012 cm−2. Two ohmic contacts were deposited on the sample surface and annealed in order to contact the buried QD layers. The dots exhibit TM polarized absorption linked to the s–pz transition. The photocurrent at 300 K is slightly blue-shifted with respect to the s–pz intraband absorption. The responsivity increases exponentially with temperature and reaches a record value of 10 mA/W at 300 K for detectors with interdigitated contacts. 相似文献
13.
The ground-state binding energy of a hydrogenic donor impurity in wurtzite (WZ) GaN/AlGaN coupled quantum dots (QDs) is calculated by means of a variational method, considering the strong built-in electric fields caused by the piezoelectricity and spontaneous polarizations. The strong built-in electric fields induce an asymmetrical distribution of the ground-state binding energy with respect to the center of the coupled QDs. If the impurity is located at the low dot, the ground-state binding energy is insensitive to the interdot barrier width of WZ GaN/AlGaN coupled QDs. 相似文献
14.
O. Yilmazoglu D. Pavlidis Yu. M. Litvin S. Hubbard I. M. Tiginyanu K. Mutamba H. L. Hartnagel V. G. Litovchenko A. Evtukh 《Applied Surface Science》2003,220(1-4):46-50
Whisker structures and quantum dots fabricated by photoelectrochemical (PEC) etching of undoped and doped metalorganic chemical vapor deposition (MOCVD)-grown GaN (2×1017 or 3×1018 cm−3) are investigated in relation with their field-emission characteristics. Different surface morphologies, corresponding to different etching time and photocurrent, results in different field-emission characteristics with low turn-on voltage down to 4 V/μm and the appearance of quantum-size effect in the I–V curves. 相似文献
15.
J.P. Garayt J.M. Grard F. Enjalbert L. Ferlazzo S. Founta E. Martinez-Guerrero F. Rol D. Araujo R. Cox B. Daudin B. Gayral Le Si Dang H. Mariette 《Physica E: Low-dimensional Systems and Nanostructures》2005,26(1-4):203
We report single dot spectroscopy of cubic GaN/AlN self-assembled quantum dots. Typical linewidths of the zero-phonon line between 2 and 8 meV are observed and interpreted in terms of charge fluctuations around a given quantum dot. The phonon sideband contribution in this emission, even at low temperature, reveals the importance of the acoustic phonon broadening mechanism which controls the exciton dephasing and may impose the real limits to the optical properties of GaN single QDs emission. 相似文献
16.
S. Lee M. Dobrowolska J.K. Furdyna 《Physica E: Low-dimensional Systems and Nanostructures》2005,26(1-4):271
We have investigated a series of double-layer structures consisting of a layer of self-assembled non-magnetic CdSe quantum dots (QDs) separated by a thin ZnSe barrier from a ZnCdMnSe diluted magnetic semiconductor (DMSs) quantum well (QW). In the series, the thickness of the ZnSe barrier ranged between 12 and 40 nm. We observe two clearly defined photoluminescence (PL) peaks in all samples, corresponding to the CdSe QDs and the ZnCdMnSe QW, respectively. The PL intensity of the QW peak is observed to decrease systematically relative to the QD peak as the thickness of the ZnSe barrier decreases, indicating a corresponding increase in carrier tunneling from the QW to the QDs. Furthermore, polarization-selective PL measurements reveal that the degree of polarization of the PL emitted by the CdSe QDs increases with decreasing thickness of the ZnSe barriers. The observed behavior is discussed in terms of anti-parallel spin interaction between carriers localized in the non-magnetic QDs and in the magnetic QWs. 相似文献
17.
J. Gomis J. Martínez-Pastor B. Alén D. Granados J. M. García P. Roussignol 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(4):471-477
We present a study of the primary optical transitions
and recombination dynamics in InGaAs self-assembled quantum
nanostructures with different shape. Starting from the same
quantum dot seeding layer, and depending on the overgrowth
conditions, these new nanostructures can be tailored in shape and
are characterized by heights lower than 2 nm and base lengths
around 100 nm. The geometrical shape strongly influences the
electronic and optical properties of these nanostructuctures. We
measure for them ground state optical transitions in the range
1.25–1.35 eV and varying energy splitting between their excited
states. The temperature dependence of the exciton recombination
dynamics is reported focusing on the intermediate temperature
regime (before thermal escape begins to be important). In this
range, an important increase of the effective photoluminescence
decay time is observed and attributed to the state filling and
exciton thermalization between excited and ground states. A rate
equation model is also developed reproducing quite well the
observed exciton dynamics. 相似文献
18.
Y. Turki-Ben Ali R. Bennaceur 《Physica E: Low-dimensional Systems and Nanostructures》2005,28(4):347-354
The aim of this work is to analyze theoretically the correlation energies for neutral, positively, negatively charged exciton and bi-exciton. So, we propose a model consistent with experimental observations that is small InAs truncated pyramids with circular base lying on wetting layer, both buried into GaAs matrix.In a first step and in contrast to other works, we are able to evaluate coulombic interactions between electron and hole, two electrons and two holes by perturbative method at the second order. In a second step, the correlation energies of many-body complexes X, X-, X+ and XX are investigated as a function of quantum dots basis radius rc and the applied electric field.Our main goal is to provide realistic estimation for the correlation energies of excitons, charged excitons and bi-excitons while retaining at the same time a transparent formalism, which could easily be transposed to structures of actual interest.The present work provides evidence of the stability of excitons, charged excitons and bi-excitons in InAs/GaAs quantum dots. Calculated correlation energies of many-body complexes are consistent with those reported by recent photoluminescence measurements. 相似文献
19.
《Comptes Rendus Physique》2008,9(8):816-829
We present here a review of the peculiar optical properties of GaN/AlN quantum dots. These systems show unusually large exciton binding energies and band-offsets. Moreover, when grown along the (0001) axis in the wurtzite phase, the optical properties are dominated by huge on-axis internal electric fields, leading to a very low oscillator strength and complex dynamical behavior. It is also possible to grow GaN quantum dots in the cubic phase or along nonpolar axis of the wurtzite cell. We discuss properties of ensembles of quantum dots, as well as of single quantum dots studied by micro-photoluminescence. To cite this article: P. Lefebvre, B. Gayral, C. R. Physique 9 (2008). 相似文献
20.
采用模拟计算的方法,运用量子点模型对GaN基LED器件中不同尺寸量子点的电致发光光谱进行模拟分析,并对器件结构中电子空穴浓度,辐射复合强度进行了研究.分析结果显示,随着量子点尺寸的增大,量子点发光波长存在红移,当圆柱状量子点半径从1.8nm增长到13nm时,波长红移309.6meV,在量子阱中生长单一尺寸的量子点可以达到不同波长的单色发光器件,而在不同量子阱中生长不同尺寸的量子点可以实现多波长发光,以及单颗LED的白色显示,并通过调节量子点的分布密度达到调节各发光波长强度的目的.结果表明,量子点分布密度调节之后多波长发光均匀性得到有效改善. 相似文献