Local Strain Effects in Near-Field Spectra of Single Semiconductor Quantum Dots.

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E7.4.1

Local Strain Effects in Near-Field Spectra of Single Semiconductor Quantum Dots. A. M. Mintairov1, P. A. Blagnov2, O. V. Kovalenkov2, C. Li3, J. L. Merz1, S. Oktyabrsky4, K. Sun1, V. Tokranov4, A. S. Vlasov2, D. A. Vinokurov2. 1

Electrical Engineering Department, University of Notre Dame, Notre Dame, IN 46556, USA Ioffe Physico-Technical Institute, RAS, 194021 St. Petersburg, Russia 3 Aerospace and Mechanical Engineering Department, University of Notre Dame, IN 46556, USA 4 UAlbany Inst. for Materials University at Albany-SUNY, 251 Fuller Rd. Albany, NY 12203 2

ABSTRACT Experimental and theoretical investigations of high-energy shifts of single InAs, InGaAs, InAlAs and InP quantum dot (QD) emission lines induced by contact pressure exerted by a nearfield optical fiber tip are reported. “Pressure” coefficients of 0.65-3.5 meV/nm have been measured for ground state emission lines in agreement with numerical calculations. We show that the observed increase of the tip-induced energy shift with increasing aperture diameter is caused by a decrease of the uniaxial strain component. We also report the effect of emission instability of single QD emission intensity under tip-induced pressure. INTRODUCTION Near-field scanning optical microscopy (NSOM) allows one to extend the spatial resolution of optical experiments far beyond the light diffraction limit, which opens new possibilities for nanoscale characterization. In the present paper we report the results of numerical calculations of the shift of the ground state emission energy of self-organized quantum dots (QDs) induced by the pressure produced by a near-field tip [1]. Comparison with experiments shows that the observed dependence of the shifts on tip diameter can be quantitatively described in terms of contributions of hydrostatic and uniaxial strain components. Unexpectedly, a strong instability of the emission intensity of single QDs has also been observed. EXPERIMENTAL DETAILS We studied the InP/GaInP, InGaAs/GaAs and InAlAs/AlAs QD samples described in [1]. The structural and elastic parameters of each sample are presented in Table 1. It should be noted that InGaAs/GaAs and InAlAs/AlAs samples have a bimodal distribution of QD sizes, which is Table.1 Structural and elastic parameters of QD samples. Matrix material*)

QD material

Density, µm-2

Base, nm

Height, nm

Young’s modulus (Y) (matrix/QD), kbar GaInP InP 20 100 10 820/611 InAs 100 7 5 861/514 GaAs/AlAs InAlAs 50 14 5 861/720 InAs 300 10 5 861/514 AlAs/GaAs InGaAs 150 22 5 861/720 *)The thickness of the cap layer for all structures is 40 nm

Poisson’s ratio (ν) (matrix/QD) 0.34/0.36 0.32/0.35 0.32/0.34 0.32/0.35 0.32/0.34

Deformation potentials [2] a/b, eV 6.5/1.8 6/1.8 7.6/2 6/1.8 7.6/2

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