Control of unpolarized emission in closely stacked InAs quantum dot structure

Fortunato, Laura; Todaro, M. T.; Tasco, V.; Giorgi, Milena De; Vittorio, Massimo De; Cingolani, R.; Passaseo, A.

doi:10.1016/j.spmi.2009.09.004

Cited by 9 publications

(13 citation statements)

References 14 publications

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“…The value of DOP depends on the chosen direction for the TE-mode in the plane of quantum dot. While the previous studies of polarization response of quantum dots provide only one value of DOP corresponding to a chosen direction for the TEmode 3,4,12,33 , we associate DOP with the direction of TE-mode, for example TE 110 → DOP 110 and TE1 10 → DOP1 10 , and show that the DOP depends highly on the chosen direction. Only one DOP value is not sufficient to fully characterize the polarization response of quantum dots systems.…”

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confidence: 71%

Experimental and atomistic theoretical study of degree of polarization from multilayer InAs/GaAs quantum dot stacks

Usman¹,

et al. 2011

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Recent experimental measurements, without any theoretical guidance, showed that isotropic polarization response can be achieved by increasing the number of QD layers in a QD stack. Here we analyse the polarization response of multi-layer quantum dot stacks containing up to nine quantum dot layers by linearly polarized PL measurements and by carrying out a systematic set of multi-million atom simulations. The atomistic modeling and simulations allow us to include correct symmetry properties in the calculations of the optical spectra: a factor critical to explain the experimental evidence. The values of the degree of polarization (DOP) calculated from our model follows the trends of the experimental data. We also present detailed physical insight by examining strain profiles, band edges diagrams and wave function plots. Multi-directional PL measurements and calculations of the DOP reveal a unique property of InAs quantum dot stacks that the TE response is anisotropic in the plane of the stacks. Therefore a single value of the DOP is not sufficient to fully characterize the polarization response. We explain this anisotropy of the TE-modes by orientation of hole wave functions along the [110] direction. Our results provide a new insight that isotropic polarization response measured in the experimental PL spectra is due to two factors: (i) TM001-mode contributions increase due to enhanced intermixing of HH and LH bands, and (ii) TE110-mode contributions reduce significantly due to hole wave function alignment along the [110] direction. We also present optical spectra for various geometry configurations of quantum dot stacks to provide a guide to experimentalists for the design of multi-layer QD stacks for optical devices. Our results predict that the QD stacks with identical layers will exhibit lower values of the DOP than the stacks with non-identical layers.

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confidence: 71%

Experimental and atomistic theoretical study of degree of polarization from multilayer InAs/GaAs quantum dot stacks

Usman¹,

et al. 2011

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“…[1][2][3][4] The optical properties of QDs are of critical importance because they can be used to control the polarization sensitivity of devices. Several approaches have been explored in order to achieve polarization-insensitive emission from QDs, including covering the QDs with a strain reducing layer, 5 growing multiple electronically coupled layers of QDs [6][7][8] and columnar QDs, 9,10 and forming a type-II band alignment using GaAsSb barriers. 11 However, to date, there has not been much theoretical guidance available to help people fully understand the optical properties of these QDs.…”

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confidence: 99%

Experimental and theoretical study of polarization-dependent optical transitions in InAs quantum dots at telecommunication-wavelengths (1300-1500 nm)

Usman

Heck

Clarke

et al. 2011

Journal of Applied Physics

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The design of some optical devices such as semiconductor optical amplifiers for telecommunication applications requires polarization-insensitive optical emission at the long wavelengths (1300-1550 nm). Self-assembled InAs/GaAs quantum dots (QDs) typically exhibit ground state optical emission at wavelengths shorter than 1300 nm with highly polarization-sensitive characteristics, although this can be modified by using low growth rates, the incorporation of strainreducing capping layers or growth of closely-stacked QD layers. Exploiting the strain interactions between closely stacked QD layers also allows greater freedom in the choice of growth conditions for the upper layers, so that both a significant extension in their emission wavelength and an improved polarization response can be achieved due to modification of the QD size, strain and composition. In this paper we investigate the polarization behavior of single and stacked QD layers using room temperature sub-lasing-threshold electroluminescence and photovoltage measurements as well as atomistic modeling with the NEMO 3-D simulator. A reduction is observed in the ratio of the transverse electric (TE) to transverse magnetic (TM) optical mode response for a GaAs-capped QD stack compared to a single QD layer, but when the second layer of the two-layer stack is InGaAs-capped an increase in the TE/TM ratio is observed, in contrast to recent reports for single QD layers.

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“…Thus, a directional degree of polarization (DOP) should be measured (or calculated) to fully characterize the polarization response of quantum dot stacks. Previous theoretical and experimental studies have considered only a single value of DOP: either [110] The electronic structure of single and stacked InAs quantum dots (QDs) has been extensively studied in the last couple of decades for the design of optical devices [1][2][3][4][5][6][7][8] and devices suited to quantum information processing. [9][10][11][12] Recent efforts are focused to achieve isotropic polarization response of ground state optical intensity (GSOI) at telecommunication wavelengths (1300-1500 nm).…”

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“…[9][10][11][12] Recent efforts are focused to achieve isotropic polarization response of ground state optical intensity (GSOI) at telecommunication wavelengths (1300-1500 nm). 2,[4][5][6][7] The polarization response of QD samples is characterized in terms of degree of polarization:…”

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In-plane polarization anisotropy of ground state optical intensity in InAs/GaAs quantum dots

Usman¹

2011

Journal of Applied Physics

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The design of optical devices such as lasers and semiconductor optical amplifiers for telecommunication applications requires polarization insensitive optical emissions in the region of 1500 nm. Recent experimental measurements of the optical properties of stacked quantum dots have demonstrated that this can be achieved via exploitation of inter-dot strain interactions. In particular, the relatively large aspect ratio (AR) of quantum dots in the optically active layers of such stacks provide a two-fold advantage, both by inducing a red shift of the gap wavelength above 1300 nm, and increasing the TM001-mode, thereby decreasing the anisotropy of the polarization response. However, in large aspect ratio quantum dots (AR > 0.25), the hole confinement is significantly modified compared with that in lower AR dots-this modified confinement is manifest in the interfacial confinement of holes in the system. Since the contributions to the ground state optical intensity (GSOI) are dominated by lower-lying valence states, we therefore propose that the room temperature GSOI be a cumulative sum of optical transitions from multiple valence states. This then extends previous theoretical studies of flat (low AR) quantum dots, in which contributions arising only from the highest valence state or optical transitions between individual valence states were considered. The interfacial hole distributions also increases in-plane anisotropy in tall (high AR) quantum dots (TE110 not equal TE-110), an effect that has not been previously observed in flat quantum dots. Thus, a directional degree of polarization (DOP) should be measured (or calculated) to fully characterize the polarization response of quantum dot stacks. Previous theoretical and experimental studies have considered only a single value of DOP: either [110] or [-110]. (C) 2011 American Institute of Physics. [doi:10.1063/1.3657783

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Control of unpolarized emission in closely stacked InAs quantum dot structure

Cited by 9 publications

References 14 publications

Experimental and atomistic theoretical study of degree of polarization from multilayer InAs/GaAs quantum dot stacks

Experimental and atomistic theoretical study of degree of polarization from multilayer InAs/GaAs quantum dot stacks

Experimental and theoretical study of polarization-dependent optical transitions in InAs quantum dots at telecommunication-wavelengths (1300-1500 nm)

In-plane polarization anisotropy of ground state optical intensity in InAs/GaAs quantum dots

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