Near-Field Optical Mapping of Exciton Wave Functions in a GaAs Quantum Dot

Matsuda, Kazunari; Saiki, Takanao; Nomura, Sakashi; Mihara, M.; Aoyagi, Yoshinobu; Nair, Selvakumar V.; Takagahara, Toshihide

doi:10.1103/physrevlett.91.177401

Cited by 165 publications

(83 citation statements)

References 27 publications

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“…10 Near-field spectroscopy has made a remarkable contribution to investigations of the optical properties in nanocrystallite, 11 and has resulted in the observation of nanometer-scale optical images, such as the local density of exciton states. 12 However, reports on semiconductor quantum structure are limited to naturally formed quantum dots ͑QDs͒. 12-14 Here we report low-temperature near-field spectroscopy of artificially fabricated ZnO SQWs on the end of a ZnO nanorod.…”

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confidence: 99%

Near-field measurement of spectral anisotropy and optical absorption of isolated ZnO nanorod single-quantum-well structures

Yatsui

Ohtsu

Yoo

et al. 2005

Applied Physics Letters

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We report low-temperature near-field spectroscopy of isolated ZnO / ZnMgO single-quantum-well structures ͑SQWs͒ on the end of ZnO nanorod to define their potential for nanophotonics. First, absorption spectra of isolated ZnO / ZnMgO nanorod SQWs with the Stokes shift as small as 3 meV and very sharp photoluminescent peaks indicate that the nanorod SQWs are of very high optical quality. Furthermore, we performed polarization spectroscopy of isolated ZnO SQWs, and observed valence-band anisotropy of ZnO SQWs in photoluminescence spectra directly. Since the exciton in a quantum structure is an ideal two-level system with long coherence times, our results provide criteria for designing nanophotonic devices. © 2005 American Institute of Physics. ͓DOI: 10.1063/1.1990247͔ ZnO nanocrystallites are a promising material for realizing nanometer-scale photonic devices, 1 i.e., nanophotonic devices, at room temperature, owing to their large exciton binding energy 2-4 and large oscillator strength. 5 Furthermore, the recent demonstration of semiconductor nanorod quantumwell structures enables us to fabricate nanometer-scale electronic and photonic devices on single nanorods. [6][7][8][9] Recently, ZnO / ZnMgO nanorod heterostructures were fabricated and the quantum confinement effect even from the singlequantum-well structures ͑SQWs͒ was observed. 10 Near-field spectroscopy has made a remarkable contribution to investigations of the optical properties in nanocrystallite, 11 and has resulted in the observation of nanometer-scale optical images, such as the local density of exciton states. 12 However, reports on semiconductor quantum structure are limited to naturally formed quantum dots ͑QDs͒. 12-14 Here we report low-temperature near-field spectroscopy of artificially fabricated ZnO SQWs on the end of a ZnO nanorod.ZnO / ZnMgO SQWs were fabricated on the ends of ZnO stems with a mean diameter of 40 nm and a length of 1 m using catalyst-free metalorganic vapor phase epitxy, in which the ZnO nanorods were grown vertically from a sapphire ͑0001͒ substrate in the c orientation. 10,15 The Mg concentration in the ZnMgO layers averaged 20 at. %. Two samples were prepared for this study: their ZnO well layer thickness L w , were 2.5 and 3.75 nm, while the thicknesses of the ZnMgO bottom and top barrier layers in the SQWs were fixed at 60 and 18 nm, respectively. After growing the ZnO / ZnMgO nanorod SQWs, they were dispersed so that they were laid down on a flat sapphire substrate to isolate them from each other ͓Fig. 1͑a͔͒.The far-field photoluminescence ͑PL͒ spectra were obtained using a He-Cd laser ͑ = 325 nm͒ before dispersion of the ZnO / ZnMgO nanorod SQWs. The emission signal was collected with the acromatic lens ͑f =50 mm͒. To confirm that the optical qualities of individual ZnO / ZnMgO SQWs were sufficiently high, we used a collection-mode near-field optical microscope ͑NOM͒ using a He-Cd laser ͑ = 325 nm͒ for excitation, and a UV fiber probe with an aperture diameter of 30 nm. The excitation source was focused on a nanorod ...

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mentioning

confidence: 99%

Near-field measurement of spectral anisotropy and optical absorption of isolated ZnO nanorod single-quantum-well structures

Yatsui

Ohtsu

Yoo

et al. 2005

Applied Physics Letters

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“…8). Such a doublet structure is similar to that observed in the micro-luminescence of natural GaAs and InAs quantum dots [9][10][11][12][13][14], and can be assigned to neutral (X) and charged excitons and/or biexcitons (XX1). A further increase in the excitation power leads to the appearance of additional low energy lines which we attribute to the formation of more complex excitonic molecules (lines XX2 and XX3).…”

Section: Micro-luminescence Experimentsmentioning

confidence: 58%

“…Quadratic and cubic dependences were observed for the XX1 and XX3 lines, respectively. Such behavior was already observed for GaAs QDs [9,14] and per analogy, the excitonic emission can be attributed to the recombination of the neutral exciton, biexciton, tri-exciton, and higher order excitonic complexes [15]. In the high excitation regime the subsequent emissions saturate when the emissions of more complex structures gain in intensity.…”

Section: Micro-luminescence Experimentsmentioning

confidence: 77%

Emission from Mesoscopic-Size Islands Formed in a GaAs/AlAs Double Layer Structure

et al. 2004

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The nature of sharp emission lines which are present in macro--luminescence experiments on a type-II GaAs/AlAs double quantum well structure is discussed. The experiments, which also include micro-luminescence measurements, allowed us to conclude that the sharp emission lines observed originate from lateral GaAlAs islands of a few µm in diameter. They serve as efficient type-I recombination centers for indirect excitons and/or carriers which diffuse in the GaAs/AlAs QW structure and strongly affect the emission processes observed in macro-luminescence experiments. These traps can easily be filled with electron-hole pairs, giving rise to the formation of neutral excitons as well as more complex excitonic molecules. Magnetoluminescence spectra from single islands resemble those observed for natural quantum dots formed in narrow GaAs quantum wells.

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“…This technique has been used to study the charge build-up in the quantum wells [2], transport and accumulation of optically excited minority carriers in the same device [3] and more recently as an imaging spectroscopy to map out the center-of-mass wave functions of an exciton confined in a GaAs quantum dot [4]. The PL signal, which provide the most important information on the mechanisms of operation of resonant tunneling diodes, arise from recombination between electrons, which tunnel into the quantum well (QW), and holes photocreated in the n + GaAs region of the structure and then tunneled into the QW.…”

Section: Introductionmentioning

confidence: 99%

Influence of minority carrier transport in the optical properties of double barrier diodes

et al. 2006

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The aim of this work is to study the importance of minority carrier transport in double barrier diodes (DBD). We propose a theoretical model capable to describe the photoluminescence properties observed in GaAs − Al 0.35 Ga 0.65 As double barrier diodes with the increase of temperature. In this model, we considered that the minority carries (holes) photocreated at the contact of the structure diffuse, drift and then tunnel to the well. To study the influence of previous transport mechanisms, we solved the continuity equation under the influence of an applied bias and an excitation laser light. The theoretical photocurrent and photoluminescence calculations agree quite well with the experimental observations. Within the approaches of our model, we are able to simulate the minority holes mobility from the photocurrent measurements suggesting the use of the experimental technique as a probe of the carrier mobility.

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Near-Field Optical Mapping of Exciton Wave Functions in a GaAs Quantum Dot

Cited by 165 publications

References 27 publications

Near-field measurement of spectral anisotropy and optical absorption of isolated ZnO nanorod single-quantum-well structures

Near-field measurement of spectral anisotropy and optical absorption of isolated ZnO nanorod single-quantum-well structures

Emission from Mesoscopic-Size Islands Formed in a GaAs/AlAs Double Layer Structure

Influence of minority carrier transport in the optical properties of double barrier diodes

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