Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session J22: Optical Properties and Interactions in Quantum Dots and Wells |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Michael Scheibner, University of California, Merced Room: 324 |
Tuesday, March 19, 2013 2:30PM - 2:42PM |
J22.00001: Temperature dependence of highly homogeneous excitonic spectra of site-controlled pyramidal quantum dots Valentina Troncale, Emanuele Pelucchi, Alok Rudra, Eli Kapon Site-controlled pyramidal quantum dots grown by MOVPE on patterned GaAs substrates offer many advantages such as emission wavelength, heterostructure tailoring and higher symmetry for efficient photon entanglement. We address the temperature dependence of X, 2X, X-, X$+$ exciton linewidths, providing insight on exciton-phonon interaction in this system. The investigated structures consist of GaAs/AlGaAs pyramidal QDs, positioned on 5$\mu$m centers, characterized using non-resonant micro-photolumionescence at low temperatures. PL spectra of individual QDs are highly reproducible, showing transitions excitons with inhomogeneous brodening as low as 2 meV, caused by slight thickness/composition fluctuations. Interferometric T-dependent linewidth measurements of the four excitonic transitions revealed values at T$=$0 K smaller than previously reported but larger than the estimated exciton radiative lifetime. We conclude that even at T$=$0 K the exciton decoherence time in GaAs QDs is not completely governed by a radiative lifetime and discuss this effect. [Preview Abstract] |
Tuesday, March 19, 2013 2:42PM - 2:54PM |
J22.00002: Carrier Dynamics in Site-Controlled InGaN/GaN Quantum Dots Tyler Hill, Lei Zhang, Hui Deng, Chu-Hsiang Teng, Brandon Demory, Pei-Cheng Ku We investigate the individual micro-photoluminescence and time resolved photoluminescence properties of several hundred site-controlled InGaN/GaN quantum dots fabricated ``top down'' by plasma etching. The optical properties of semiconductor quantum dots can be very inhomogeneous due to small fluctuations in dot size, compositions, growth conditions, or doping levels. Controlled variation of growth conditions combined with the knowledge of experimental uncertainties in the semiconductor properties allows for a statistical analysis to obtain quantitative correlations between the optical properties of the quantum dots and the growth conditions or structural properties. We find that, with an indium fraction of 10-15\%, quantum dots with diameters smaller than 33 nm show markedly different carrier dynamics than those with a diameter larger than 60nm: 1) fluctuations in indium mole fraction or monolayer fluctuations in the InGaN layer have a more significant effect on photoluminescence than changing dot diameter; 2) non-radiative decay related to surface recombination is the dominant decay channel in the system; 3) Increasing surface to volume ratio helps suppress the internal quantum efficiency of multi-exciton states, leading to more strongly antibunched photon sources. [Preview Abstract] |
Tuesday, March 19, 2013 2:54PM - 3:06PM |
J22.00003: Narrow optical line width from site-controlled InGaAs quantum dots Lily Yang, Michael Yakes, Timothy Sweeney, Samuel Carter, Chulsoo Kim, Mijin Kim, Allan Bracker, Daniel Gammon The incorporation of self-assembled quantum dots (QDs) in systematically scalable quantum devices requires a method of nucleating dots with nanometer-scale spatial accuracy while preserving their narrow optical line width. We have developed a technique combining e-beam lithography, wet etching, and molecular beam epitaxial (MBE) growth to deterministically position InGaAs QDs with spectrometer limited photoluminescence line widths. Our technique takes advantage of the anisotropy in GaAs growth to evolve an etched pattern of holes and lines into faceted structures in which dots nucleate. Using this technique, we were able to grow a buffer layer of pure GaAs up to 90 nm in thickness between the processed surface and the dot nucleation surface, effectively separating the QDs from unavoidable residual defects and impurities on the patterned surface that broaden their optical line widths. Additionally, we demonstrate control over the number of dots nucleating per site, from single to a chain of several, by varying the dimensions of the original pattern. Our dots are grown in a Schottky diode structure. Their PL spectrum shows discrete charging transitions, with narrow linewidths near the spectrometer's resolution limit of 20 micro eV. [Preview Abstract] |
Tuesday, March 19, 2013 3:06PM - 3:18PM |
J22.00004: Eliminating the fine structure splitting of excitons in self-assembled InAs/GaAs quantum dots via combined stresses Lixin He, Jianping Wang, Ming Gong, G.-C. Guo Eliminating the fine structure splitting (FSS) of excitons in self-assembled quantum dots (QDs) is essential to the generation of high quality entangled photon pairs. We show by a extended two-level model that the FSS of excitons in a general self-assembled InGaAs/GaAs QD can be fully suppressed via combined stresses along the [110] and [010] directions. The results of the model Hamiltonian are confirmed by atomic empirical pseudopotential calculations. For all the QDs we calculated, the FSS can be tuned to be vanishingly small ($<$ 0.1 $\mu$eV), which is sufficient small for high quality entangled photon emission. [Preview Abstract] |
Tuesday, March 19, 2013 3:18PM - 3:30PM |
J22.00005: Rabi-Kondo correlated state in a laser-driven quantum dot Moshe Goldstein, Bjoern Sbierski, Markus Hanl, Andreas Weichselbaum, Hakan Tureci, Leonid Glazman, Jan von Delft, Atac Imamoglu Spin exchange between a single-electron charged quantum dot and itinerant electrons leads to the emergence of Kondo screening. When the quantum dot is driven resonantly by a weak laser light, the resulting emission spectrum serves as a direct probe of these correlations. In the opposite limit of vanishing exchange interaction and strong laser drive, the quantum dot exhibits coherent Rabi oscillations between the single-spin and optically excited states at the ``bare'' frequency $\Omega$. Here we show that the interplay between strong exchange and non-perturbative laser coupling leads to the formation of a new non-equilibrium quantum-correlated state, featuring a second screening cloud. We elucidate the signatures of that state in the spectrum of luminescence. The spectrum consists of a delta-function peak at the laser light frequency (the peak weight scales as $\Omega^{2/3}$) and a broad peak red-shifted by the renormalized Rabi frequency $\Omega^{*} \propto \Omega^{4/3}$. The shape of the broad peak carries detailed information about the spin screening cloud. [Preview Abstract] |
Tuesday, March 19, 2013 3:30PM - 3:42PM |
J22.00006: Adiabatic rapid passage in single InGaAs quantum dots: Towards a method of ``incoherent control'' Peter Brereton, Megan Stanley, Alexandra Graham, Barbara Van Hattem, Pierre Corfdir, Isobel Houghton, Yanwen Wu, Mark Hopkinson, Richard Phillips Adiabatic rapid passage (ARP) using frequency-swept optical pulses was shown to invert an InGaAs quantum dot from the ground state to the neutral exciton state [1,2]. As in atomic systems, ARP couples the confined electronic states of a quantum dot to a pulse that is chirped to sweep through resonance. If the sweep rate is slow with respect to the instantaneous Rabi frequency but faster than any decay rates, the dressed state of the system will adiabatically switch from one bare state to the other. Damping of the ARP inversion suggests confirmation of theoretical predictions of the effect of phonon-assisted dephasing [3]. ARP allows a train of chirped pulses to control the population state of a quantum dot without the need for locking the relative phase of the pulses. Each pulse pair will effectively drive the state vector through a \(2\pi\) rotation on the Bloch sphere, regardless of the relative phase. Initial work toward this method of `incoherent control' is presented, showing an enhancement of the photocurrent under excitation with two chirped pulses separated by greater than the electron tunneling time. [1] Y. Wu, et al, PRL 106, 067401 (2011). [2] C.-M. Simon, et al PRL, 106, 166801 (2011). [3] A. Debnath, et al PRB, 86, 161304 (2012). [Preview Abstract] |
Tuesday, March 19, 2013 3:42PM - 3:54PM |
J22.00007: Investigation of exciton states under two color optical excitation in quantum dot molecules Ramana Thota, Eric Stinaff, Allan Bracker, Dan Gammon It has been shown that vertically stacked InAs quantum dots may form quantum dot molecules (QDMs) where the tunneling of the carriers results in molecular wavefunction formation. These states are potentially useful for the preparation and manipulation of entangled spins, necessary components for quantum information processing. It has also been previously shown that certain charged exciton states can be created optically resulting in a straightforward method for optical spin initialization. We will present a study of optical charge state creation in vertically stacked In$_{\mathrm{x}}$Ga$_{\mathrm{1-x}}$As quantum dots grown by molecular beam epitaxy. This includes using a two color micro-photoluminescence experiment where we tune one laser through the states associated with the quantum dot (resonant excitation) and keep the other laser fixed with its excitation at the energy of the wetting layer (non-resonant excitation). This technique may result in a method for enhancement of various charged and neutral exciton states. In particular we have investigated the doubly charged exciton state, where the ground state is two spins in a know configuration, as well as biexciton enhancement, possibly useful for generating entangle photon pairs. [Preview Abstract] |
Tuesday, March 19, 2013 3:54PM - 4:06PM |
J22.00008: Coulomb interaction signatures in self-assembled lateral quantum dot molecules Xinran Zhou, Jihoon Lee, Gregory Salamo, Miquel Royo, Juan Climente, Matthew Doty Lateral quantum dot molecules (LQDMs) consist of at least two closely spaced InGaAs quantum dots arranged along axes perpendicular to the growth direction. Coherent interactions between neighboring QDs can lead to the formation of delocalized states with unique and useful properties. LQDMs provide an opportunity for independent control of both coupling and charge occupancy, and are thus of interest for prototype devices that use the QDs as bit registers. The experimental evidence for the existence of delocalized states and inter-dot tunneling in LQDMs, limited by the large center-to-center distance and weak tunneling strength, has been indirect. We use photoluminescence spectroscopy to investigate the ground state of single LQDMs. We apply a voltage along the growth direction that allows us to control the total charge occupancy of the quantum dot molecule. Using a combination of computational modeling and experimental analysis, we assign the observed discrete spectral lines to specific charge distributions. We explain the dynamic processes that lead to these charge configurations through electrical injection and optical generation. Our systemic analysis provides experimental evidence of inter-dot tunneling of electrons as predicted in previous theoretical work. [Preview Abstract] |
Tuesday, March 19, 2013 4:06PM - 4:18PM |
J22.00009: Study of optical and electronic properties of self-assembled InAs/GaAs quantum rings Gabriel Linares, Samar Alsolamy, Morgan Ware, Yuriy Mazur, Zhiming Wang, Jihoon Lee, Greg Salamo, Eric Stinaff, Lilia Meza-Montes We will present a theoretical study of the properties of self assembled InAs/GaAs quantum rings. These nanostructures are grown by metal droplet epitaxy and do not follow the traditional strain driven growth model. For certain growth conditions, two quantum dots are formed on the ring structure which then, in a sense, acts as a wetting ring. A `wetting layer' of 2D InAs is formed by migrating InAs material away from the initial In droplet. We have calculated the eigenstates of electrons and holes inside of the nanostructure using \textbf{k\textbullet p }theory, within the 1 and 4 bands approximation. We include effects such as the strain, the concentration of Indium and external electric field. The wave functions are then used to calculate optical properties and the energies of various exciton states as a function of the indium concentration and distribution. These results are compared with photoluminescence data on existing structures grown under different conditions. The energies of the various states along with the possibility of energy transfer between the dots will be explored. [Preview Abstract] |
Tuesday, March 19, 2013 4:18PM - 4:30PM |
J22.00010: Luminescence studies of pairs of quantum dots formed on quantum rings by droplet epitaxy Samar Alsolamy, Morgan Ware, Yuriy Mazur, Zhiming Wang, Jihoon Lee, Greg Salamo, G. Linares, Lilia Meza-Montes, Eric Stinaff The use of metal droplet epitaxy may provide a novel method of growing laterally coupled nanostructures. We will present optical studies of InAs/GaAs nanostructures which result in twin quantum dots (QD) formed on a quantum ring (QR). Previous studies have investigated the coupling between vertically grown quantum dot pairs. Here we have used photoluminescence (PL) and photoluminescence excitation (PLE) to examine the possibility of energy transfer and coupling between quantum dot pairs in a single InGaAs quantum ring grown by droplet epitaxy. Power dependent photoluminescence spectra reveals a few peaks at low power, which are identified with emission from the ground state of the individual dots. As the power is increased we observe multi-exciton and excited state emission. We then perform PLE, tuning the excitation laser energy continuously from the high energy ring emission down to the individual dot states. We have observed resonant PLE emission in the QD/QR structures both at high energy and when resonant with the indentified ground states of one of the QDs which may indicate energy transfer and/or coupling between the dots. [Preview Abstract] |
Tuesday, March 19, 2013 4:30PM - 4:42PM |
J22.00011: Coulomb Enhancement of Superfluorescence Bursts from the Fermi Edge in Highly-Excited Quantum Wells Ji-Hee Kim, Tim Noe, Stephen A. McGill, Yongrui Wang, Aleksander K. W\'ojcik, Alexey A. Belyanin, Junichiro Kono Superfluorescence (SF) is a many-body process in which an ensemble of excited dipoles spontaneously develops macroscopic coherence and abruptly decays by producing a burst of coherent radiation. We have recently reported the first observation of SF from semiconductor quantum wells in the presence of a strong perpendicular magnetic field [1]. Here, we report on results of our systematic magnetic field dependent studies of light emission from high-density electron-hole systems with gain. We observed SF pulses even at 0 Tesla when the excitation power is high and the temperature is low. The SF radiation at 0 Tesla shows a continuous band of emission in time-resolved photoluminescence images, i.e., the photon energy of the emitted light changes continuously with time. We interpret this phenomenon in terms of Coulomb enhancement of gain near the Fermi energy in a high-density electron-hole system. In addition, we demonstrate that the delay between the pump pulse and the SF pulses is tunable through the magnetic field and excitation pump power. Finally, the delay is longer for a lower-energy Landau level at a given magnetic field, i.e., the SF bursts proceed in a sequential manner from higher to lower Landau levels. \\[4pt] [1] Noe \textit{et al.}, Nature 8, 219 (2012) [Preview Abstract] |
Tuesday, March 19, 2013 4:42PM - 4:54PM |
J22.00012: Comparative Study on Intersubband Absorption in AlGaN/GaN and AlInN/GaN Heterostructures Grown on Low-Defect Substrates Colin Edmunds, Liang Tang, Jiayi Shao, Donghui Li, Geoff Gardner, Michael Manfra, Oana Malis, Andrew Grier, Zoran Ikonic, Paul Harrison, Dimitri Zakharov Intersubband (ISB) devices utilizing III-nitrides have attracted attention for near- and far-infrared optoelectronic applications. However, the lattice mismatch between GaN and commonly used substrates results in a high defect density that hinders the vertical transport required for these devices. Furthermore, most devices in the literature utilize AlGaN/GaN heterostructures for which there is no lattice-matched alloy composition. Due to this lattice mismatch, AlGaN is not ideal for the development of complex devices such as quantum cascade lasers that often require active-region thicknesses on the order of microns for efficient operation. Fortunately, exact lattice matching occurs in AlInN/GaN heterostructures at roughly 18{\%} In composition. To investigate the challenges of lattice-matched nitrides, we presents a comparative study of ISB absorption in high-quality AlGaN/GaN and near lattice-matched AlInN/GaN heterostructures grown by molecular-beam epitaxy on low-defect free-standing GaN substrates. Experimental measurements of transition energy, integrated absorbance and linewidth were compared to theoretical predictions that included many-body effects, interface roughness and calculations of the transition lifetime. [Preview Abstract] |
Tuesday, March 19, 2013 4:54PM - 5:06PM |
J22.00013: Coulomb correlation effects and density dependence of radiative recombination rates in polar AlGaN quantum wells Greg Rupper, Sergey Rudin, Francesco Bertazzi, Gregory Garrett, Michael Wraback AlGaN narrow quantum wells are important elements of deep-ultraviolet light emitting devices. The electron-hole radiative recombination rates are important characteristics of these nanostructures. In this work we evaluated their dependence on carrier density and lattice temperature and compared our theoretical results with the experimentally determined radiative lifetimes in the c-plane grown AlGaN quantum wells. The bands were determined in the k$\cdot$p approximation for a strained c-plane wurtzite quantum well and polarization fields were included in the model. In order to account for Coulomb correlations at relatively high densities of photo-excited electron-hole plasma and arbitrary temperature, we employed real-time Green's function formalism with self-energies evaluated in the self-consistent T-matrix approximation. The luminescence spectrum was obtained from the susceptibility by summing over scattering in-plane directions and polarization states. The recombination coefficient was obtained from the integrated photo-luminescence. The density dependence of the radiative recombination rate shows effects of strong screening of the polarization electric field at high photo-excitation density. [Preview Abstract] |
Tuesday, March 19, 2013 5:06PM - 5:18PM |
J22.00014: Second quantum state transitions in GaAs/AlGaAs Bragg MQW photonic crystal probed by Optical Reflectance and Electroreflectance Yuechao Chen, Z. Liu, M.L. Nakarmi, V.V. Chaldyshev Electroreflectance spectroscopy measurement provides sharp and derivative-like spectral features in the energy region of excitonic transitions, while suppressing uninteresting background effects due to electro-modulation. We employed both electroreflectance and optical reflectance spectroscopies to probe excitonic transitions in a GaAs/AlGaAs multiple quantum well (MQW) structure. The sample used in this experiment consists of 60 periods of quantum well structures with GaAs well layer (13 nm) and AlGaAs barrier layer (94 nm), grown by solid source molecular beam expitaxy on a semi-insulating GaAs substrate. We performed electroreflectance and optical reflectance measurements by tuning the incident angle to coincide the second state of the heavy hole exciton (e2-hh2) transitions and the Bragg resonance. We observed a significant enhancement of excitonic features at the (e2-hh2) exciton transitions around incident angle of 23 degree in both techniques, revealing the double resonance condition. In the temperature dependent measurement of electroreflectance under the double resonance condition, we observed redshift of the excitonic features with increasing temperature. We will also discuss the effect of polarization in the electroreflectance measurements. [Preview Abstract] |
Tuesday, March 19, 2013 5:18PM - 5:30PM |
J22.00015: Equispaced level in the quantum well calculated for seven semiconductor ternary alloys conduction band Arthur Ejere, Godfrey Akpojotor A model of equispaced-level conduction band in semiconductor quantum well (QW) nanostructures is derived. The procedure starts with the effective-mass Schrodinger equation, with the local conduction-band edge as the potential experienced by an electron in the QW. Then the effective-mass Schrodinger equation with linear harmonic potential is made to coincide with it . In this study, an attempt has been made to model some semiconductor ternary alloys (A$_{\mathrm{x}}$B$_{\mathrm{1-x}}$C) using this procedure, thereby adding to the varieties of QW nanostructures designs in existence. Two models are derived, one with a confining potential that may be realized by appropriate grading of the semiconductor alloy and the other with a non-confining potential where the electron effective-mass tends to zero as z tends to infinity [m($z\to \pm \infty )\to 0)$. This latter type of model is not realizable. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700