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Time Correlated Single Photon Spectroscopy on Pyramidal Quantum Dots
Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
2015 (Engelska)Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Generation of non-classical light is both of fundamental interest and a common condition for quantum information applications (QIA). One feasible type of single photon emitter for QIA is based on semiconductor quantum dots (QDs), due to their atomic-like energy structure and their possibility to be integrated with other semiconductor devices on the same chip. Sitecontrolled QDs with highly linear polarized emission are a prerequisite for certain QIA and a close to room temperature operation is demanded for widespread applications.

III-nitride QD can have the deep connement potentials needed for high temperature operation, and the demonstration of single photon emission at room temperature was recently reported for a GaN QD [Nano Lett. 14, 982 (2014)]. Asymmetric III-nitride QD emits light with a high degree of linear polarization. To make site-controlled nitride-based QDs a promising approach is to deposit a thin layer of InGaN on top of hexagonal GaN micropyramids. QDs formed on the apex of the pyramids grown with this approach have been shown to exhibit single and sharp InGaN related emission lines with a high degree of linear polarization [Nano Lett. 11, 2415 (2011)]. A simple elongation of the pyramid base gives control of the polarization direction [Light: Sci. Appl. 3, e139 (2014)].

The work presented in this thesis deals with time correlation measurements, to measure, for the rst time, the single photon properties of these pyramidal QDs.

A time correlated single photon spectroscopy (TCSPS) setup was assembled, tested and used to perform measurements on these pyramidal QDs. The TCSPS apparatus measures the time dierences between subsequent photons emitted from the sample. In the spectrally ltered light of one emission line in the emission spectra, e.g. exciton emission, of a QD two or more photons cannot be emitted simultaneously, i.e. the photons are sent out one by one. A histogram of the ensemble of measured time dierences (~106 events) will then for the ideal case have no events for τ = 0, and very few for close to zero. This histogram, when normalized, is under certain conditions equal to the second order coherence function g(2)(τ ). In reality, however, there are photons coming from other sources close to the QD, i.e. background emission, that reach the detector and reduce the dip in the correlation histogram for small τ. There is also an statistical uncertainty in the measured time dierences and nally the nite bin width used in the histogram that deteriorate the measured correlation function. To understand the in uence on g(2)(τ) from background emission, instrument response function and the bin width, on the measurement on excitonic emission, simulations and calculations were made. The crucial variables were, for our samples and setup, the level of the background emission and the instrument response function.

A post growth process was developed to cover the lower parts of the pyramid sides as well as the area between the pyramids with a metal lm, to reduce the background emission. This reduces the background emission and largely improves the relative QD signal. As a result, signicant improved single photon characteristics were demonstrated.

A measurement of the second order coherence function for the excitonic autocorrelation at a temperature of 12 K, gave for zero time delay ( = 0) a value of g(2)(0) = 0.24 and the residual value of the second order coherence function (0.24) could be in full explained by the three variables, background emission, instrument response function and bin width. The g(2)(0) value for correlation measurements at higher temperatures of 50 K and 80 K is also fully explained by the three variables, showing that the emission from the QD itself is ideal up to 80 K.

This result underlines the great potential of these site controlled pyramidal dots as sources of fast polarized single photon emission, and provides the rst rigorous evidence of InGaN quantum dot formation on hexagonal GaN pyramids. We also show the rst proof of biexcitonic emission in this pyramidal QDs.

Ort, förlag, år, upplaga, sidor
Linköping: Linköping University Electronic Press, 2015. , s. 41
Serie
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1702
Nationell ämneskategori
Fysik
Identifikatorer
URN: urn:nbn:se:liu:diva-113348DOI: 10.3384/lic.diva-113348ISBN: 978-91-7519-143-0 (tryckt)OAI: oai:DiVA.org:liu-113348DiVA, id: diva2:781492
Presentation
2015-01-30, Planck, Fysikhuset, Campus Valla, Linköpints universtet, Linköping, 14:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2015-01-16 Skapad: 2015-01-16 Senast uppdaterad: 2016-06-07Bibliografiskt granskad
Delarbeten
1. Linearly polarized single photon antibunching from a site-controlled InGaN quantum dot
Öppna denna publikation i ny flik eller fönster >>Linearly polarized single photon antibunching from a site-controlled InGaN quantum dot
Visa övriga...
2014 (Engelska)Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, nr 8, s. 081901-1-081901-4Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

We report on the observation of linearly polarized single photon antibunching in the excitonic emission from a site-controlled InGaN quantum dot. The measured second order coherence function exhibits a significant dip at zero time difference, corresponding to g(m)(2) (0) = 0: 90 under continuous laser excitation. This relatively high value of g(m)(2) (0) is well understood by a model as the combination of short exciton life time (320 ps), limited experimental timing resolution and the presence of an uncorrelated broadband background emission from the sample. Our result provides the first rigorous evidence of InGaN quantum dot formation on hexagonal GaN pyramids, and it highlights a great potential in these dots as fast polarized single photon emitters if the background emission can be eliminated.

Ort, förlag, år, upplaga, sidor
American Institute of Physics (AIP), 2014
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:liu:diva-112065 (URN)10.1063/1.4893476 (DOI)000342753500022 ()
Anmärkning

Funding Agencies|Carl Trygger Foundation for Scientific Research; Swedish Research Council (VR); Nano-N consortium - Swedish Foundation for Strategic Research (SSF); Knut and Alice Wallenberg Foundation; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]; Font-D, at Linkoping University

Tillgänglig från: 2014-11-17 Skapad: 2014-11-13 Senast uppdaterad: 2017-12-05Bibliografiskt granskad
2. Polarized single photon emission and photon bunching from an InGaN quantum dot on a GaN micropyramid
Öppna denna publikation i ny flik eller fönster >>Polarized single photon emission and photon bunching from an InGaN quantum dot on a GaN micropyramid
2015 (Engelska)Ingår i: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 26, nr 6, s. 065702-Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

We report on excitonic single photon emission and biexcitonic photon bunching from an InGaN quantum dot formed on the apex of a hexagonal GaN micropyramid. An approach to suppress uncorrelated emission from the pyramid base is proposed, a metal lm is demonstrated to eectively screen background emission and thereby signicantly enhance the signal-to-background ratio of the quantum dot emission. As a result, the second order coherence function at zero time delay g(2)(0) is signicantly reduced (to g(2)(0) = 0.24, raw value) for the excitonic autocorrelation at a temperature of 12 K under continuous wave excitation, and a dominating single photon emission is demonstrated to survive up to 50 K. The deterioration of the g(2)(0)-value at elevated temperatures is well understood as the combined eect of reduced signal-to-background ratio and limited time resolution of the setup. This result underlines the great potential of site controlled pyramidal dots as sources of fast polarized single photons.

Ort, förlag, år, upplaga, sidor
Institute of Physics (IOP), 2015
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:liu:diva-113347 (URN)10.1088/0957-4484/26/6/065702 (DOI)000348448000018 ()
Tillgänglig från: 2015-01-16 Skapad: 2015-01-16 Senast uppdaterad: 2017-12-05Bibliografiskt granskad

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