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Optical Rectification and Second Harmonic Generation on Quasi-Realistic InAs/GaAs Quantum Dots: With Attention to Wetting Layer Effect  [PDF]
A. Khaledi-Nasab,M. Sabaiean,M. Sahrai,V. Fallahi
ISRN Condensed Matter Physics , 2013, DOI: 10.1155/2013/530259
Abstract: In this paper, we have performed a theoretical study on nonlinear optical rectification (OR) and second harmonic generation (SHG) for three-level dome-shaped InAs/GaAs quantum dots (QDs) in the presence of wetting layer (WL). We used the compact density matrix framework and effective mass approximation to investigate the second order nonlinear phenomena on InAs/GaAs QD. It is demonstrated that second harmonic generation (SHG), optical rectification (OR), and their mutual absorption and refractive index changes are quite sensitive to the size of QDs. The size variations have profound irregular behavior owing to distribution of envelope function on WL and QD simultaneously. Moreover it is found that ?nm is a critical radius where the regular variation takes place. It is shown that size variation causes blue shift until Critical radius ( ?nm) and after that, increasing the QD size lead to redshift in second order phenomena. 1. Introduction In the last few years the nonlinear optical properties of intersubband transitions in semiconducting materials have attracted remarkable attention due to the potential application in electronics and optoelectronics devices [1–13]. Among the semiconductor materials, zero-dimensional quantum dots (QDs) are very interesting; tunable features of QDs are one of the main reasons for this increasing performance of semiconductor QDs. The rapid advances in nanotechnology techniques such as molecular beam epitaxy (MBE) [14, 15], metal-organic chemical vapor deposition [16], and Stranski-Krastanov (S-K) [17] methods have made it possible to prepare different shape and geometry of QDs [14–18]. In QDs the carriers are confined by the confinement potential, named as quantum confinement effect in all spatial directions. Confinement provides the quantization of electronic energy levels based on the size of the dots; confinement leads to significant optical nonlinearities [11, 18]. Photons with proper energy can cause the intersublevel transitions involving large electric dipole moments [19, 20]. Among the nonlinear optical properties, the second-order nonlinear optical property plays a crucial role because it is the simplest and the lowest-order nonlinear effect; moreover, its magnitude is usually stronger than the other optical nonlinearities [21]. The second order nonlinear optical interaction of two incident fields with optical media leads to some phenomena’s like Second harmonic generation (SHG) and optical rectification (OR). To the best of our knowledge the early work on OR is dated back to 1962 by Xie and Bass et al. [21, 22] as
Size-dependent intersubband optical properties of dome-shaped InAs/GaAs quantum dots with wetting layer  [PDF]
Mohammad Sabaeian,Ali Khaledi-Nasab
Physics , 2013,
Abstract: In this work, the effect of size and wetting layer on subband electronic envelop functions, eigenenergies, linear and nonlinear absorption coefficients and refractive indices of a dome-shaped InAs/GaAs quantum dot were investigated. In our model, a dome of InAs quantum dot with its wetting layer embedded in a GaAs matrix was considered. A finite height barrier potential at the InAs/GaAs interface was assumed. To calculate envelop functions and eigenenergies, the effective one electronic band Hamiltonian and electron effective mass approximation were used. The linear and nonlinear optical properties were calculated by the density matrix formalism.
Wetting layer evolution and its temperature dependence during self assembly of InAs/GaAs quantum dots  [PDF]
Hongyi Zhang,Yonghai Chen,Guanyu Zhou,Chenguang Tang,Zhanguo Wang
Physics , 2012, DOI: 10.1186/1556-276X-7-600
Abstract: For InAs/GaAs(001) quantum dot (QD) system, the wetting layer (WL) evolution and its temperature dependence were studied using reflectance difference spectroscopy (RDS) and analyzed with a rate equation model. The WL thicknesses showed a monotonic increase at relatively low growth temperatures but a first increase and then decrease at higher temperatures, which were unexpected from the thermodynamic understanding. By adopting a rate equation model, the temperature dependence of QD growth was assigned as the origin of different WL evolutions. A brief discussion on the indium desorption was also given. Those results gave hints of the kinetic aspects of QD self-assembly.
Evolution of wetting layer in InAs/GaAs quantum dot system  [cached]
Chen YH,Ye XL,Wang ZG
Nanoscale Research Letters , 2006,
Abstract: For InAs/GaAs quantum dot system, the evolution of the wetting layer (WL) with the InAs deposition thickness has been studied by reflectance difference spectroscopy (RDS). Two transitions related to the heavy- and light-hole in the WL have been distinguished in RD spectra. Taking into account the strain and segregation effects, a model has been presented to deduce the InAs amount in the WL and the segregation coefficient of the indium atoms from the transition energies of heavy- and light-holes. The variation of the InAs amount in the WL and the segregation coefficient are found to rely closely on the growth modes. In addition, the huge dots also exhibits a strong effect on the evolution of the WL. The observed linear dependence of In segregation coefficient upon the InAs amount in the WL demonstrates that the segregation is enhanced by the strain in the WL.
Extremely Low Density InAs Quantum Dots with No Wetting Layer
HUANG She-Song,NIU Zhi-Chuan,NI Hai-Qiao,ZHAN Feng,ZHAO Huan,SUN Zheng,XIA Jian-Bai,

中国物理快报 , 2007,
Abstract: Extremely low density InAs quantum dots (QDs) are grown by molecularbeam droplet epitaxy. The gallium deposition amount is optimized tosaturate exactly the excess arsenic atoms present on the GaAs substratesurface during growth, and low density InAs/GaAs QDs (4×106cm -2) are formed by depositing 0.65 monolayers (MLs) of indium. This is much less than the critical deposition thickness (1.7ML), which is necessary to form InAs/GaAs QDs with the conventional Stranski--Krastanov growth mode. The narrowphotoluminescence linewidth of about 24meV is insensitive to cryostattemperatures from 10K to 250K. All measurements indicate that there isno wetting layer connecting the QDs.
InAs/GaAs (211)B quantum dots with negligible FSS for the generation of entangled photons  [PDF]
S. Germanis,A. Beveratos,G. E. Dialynas,G. Deligeorgis,P. G. Savvidis,Z. Hatzopoulos,N. T. Pelekanos
Physics , 2011,
Abstract: Polarization-resolved single dot spectroscopy performed on (211)B InAs/GaAs quantum dots reveals that the fine structure splitting of the excitonic levels in these dots is much lower compared to the usual (100)-grown InAs dots. Time-resolved measurements confirm the high oscillator strength of these dots, and thus their good quantum efficiency at 4 K, comparable with that of (100) InAs/GaAs dots. Last, photon correlation measurements demonstrate single photon emission out of the excitonic optical transition of these dots. All these features make this novel dot system very promising for implementing solid-state entangled photon sources.
Towards scalable entangled photon sources with self-assembled InAs/GaAs quantum dots  [PDF]
Jianping Wang,Ming Gong,G-C Guo,Lixin He
Physics , 2014, DOI: 10.1103/PhysRevLett.115.067401
Abstract: Biexciton cascade process in self-assembled quantum dots (QDs) provides an ideal system for deterministic entangled photon pair source, which is essential in quantum information science. The entangled photon pairs have recently be realized in experiments after eliminating the FSS of exciton using a number of different methods. However, so far the QDs entangled photon sources are not scalable, because the wavelengths of the QDs are different from dot to dot. Here we propose a wavelength tunable entangled photon emitter on a three dimensional stressor, in which the FSS and exciton energy can be tuned independently, allowing photon entanglement between dissimilar QDs. We confirm these results by using atomistic pseudopotential calculations. This provides a first step towards future realization of scalable entangled photon generators for quantum information applications.
Optical Characterisation of MOVPE Grown Vertically Correlated InAs/GaAs Quantum Dots  [PDF]
P. Hazdra,J. Voves,J. Oswald,K. Kuldova,A. Hospodkova,E. Hulicius,J. Pangrac
Physics , 2007,
Abstract: Structures with self-organised InAs quantum dots in a GaAs matrix were grown by the low pressure metal-organic vapour phase epitaxy (LP-MOVPE) technique. Photoluminescence in combination with photomodulated reflectance spectroscopy were used as the main characterisation methods for the growth optimisation. Results show that photoreflectance spectroscopy is an excellent tool for characterisation of QD structures wetting layers (thickness and composition) and for identification of spacers in vertically stacked QDs structures.
Effect of wetting layers on the strain and electronic structure of InAs self-assembled quantum dots  [PDF]
Seungwon Lee,Olga L. Lazarenkova,Fabiano Oyafuso,Paul von Allmen,Gerhard Klimeck
Physics , 2004, DOI: 10.1103/PhysRevB.70.125307
Abstract: The effect of wetting layers on the strain and electronic structure of InAs self-assembled quantum dots grown on GaAs is investigated with an atomistic valence-force-field model and an empirical tight-binding model. By comparing a dot with and without a wetting layer, we find that the inclusion of the wetting layer weakens the strain inside the dot by only 1% relative change, while it reduces the energy gap between a confined electron and hole level by as much as 10%. The small change in the strain distribution indicates that strain relaxes only little through the thin wetting layer. The large reduction of the energy gap is attributed to the increase of the confining-potential width rather than the change of the potential height. First-order perturbation calculations or, alternatively, the addition of an InAs disk below the quantum dot confirm this conclusion. The effect of the wetting layer on the wave function is qualitatively different for the weakly confined electron state and the strongly confined hole state. The electron wave function shifts from the buffer to the wetting layer, while the hole shifts from the dot to the wetting layer.
Composition profiling InAs quantum dots and wetting layers by atom probe tomography and cross-sectional scanning tunnelling microscopy  [PDF]
A. D. Giddings,J. G. Keizer,M. Hara,G. J. Hamhuis,H. Yuasa,H. Fukuzawa,P. M. Koenraad
Physics , 2010, DOI: 10.1103/PhysRevB.83.205308
Abstract: This study compares cross-sectional scanning tunnelling microscopy (XSTM) and atom probe tomography (APT). We use epitaxially grown self-assembled InAs quantum dots (QDs) in GaAs as an exemplary material with which to compare these two nanostructural analysis techniques. We studied the composition of the wetting layer and the QDs, and performed quantitative comparisons of the indium concentration profiles measured by each method. We show that computational models of the wetting layer and the QDs, based on experimental data, are consistent with both analytical approaches. This establishes a link between the two techniques and shows their complimentary behaviour, an advantage which we exploit in order to highlight unique features of the examined QD material.
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