Room-temperature stimulated emission of excitons in ZnO/(Mg, Zn)O superlattices

Ohtomo, Akira; Tamura, Kentaro; Kawasaki, Masashi; Makino, T.; Segawa, Y.; Tang, Zikang; Wong, George K.; Matsumoto, Yuji; Koinuma, Hideomi

doi:10.1063/1.1315340

Cited by 255 publications

(139 citation statements)

References 17 publications

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“…1,2 Additional functional devices ͑i.e., nanophotonic devices 3-6 ͒ can be realized by controlling the exciton excitation in QDs. ZnO is a promising material for room-temperature operation, owing to its large exciton binding energy [7][8][9] and recent achievements in the fabrication of nanorod heterostructures. 10,11 This study used time-resolved near-field spectroscopy to demonstrate the switching dynamics that result from controlling the optical near-field energy transfer in ZnO nanorod double-quantum-well structures ͑DQWs͒.…”

mentioning

confidence: 99%

Nanophotonic switch using ZnO nanorod double-quantum-well structures

Yatsui¹,

Sangu²,

Kawazoe³

et al. 2007

Applied Physics Letters

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The authors report on time-resolved near-field spectroscopy of ZnO / ZnMgO nanorod double-quantum-well structures ͑DQWs͒ for a nanometer-scale photonic device. They observed nutation of the population between the resonantly coupled exciton states of DQWs. Furthermore, they demonstrated switching dynamics by controlling the exciton excitation in the dipole-inactive state via an optical near field. The results of time-resolved near-field spectroscopy of isolated DQWs described here are a promising step toward designing a nanometer-scale photonic switch and related devices. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2743949͔ Systems of optically coupled quantum dots ͑QDs͒ should be applicable to quantum information processing. 1,2 Additional functional devices ͑i.e., nanophotonic devices 3-6 ͒ can be realized by controlling the exciton excitation in QDs. ZnO is a promising material for room-temperature operation, owing to its large exciton binding energy 7-9 and recent achievements in the fabrication of nanorod heterostructures. 10,11 This study used time-resolved near-field spectroscopy to demonstrate the switching dynamics that result from controlling the optical near-field energy transfer in ZnO nanorod double-quantum-well structures ͑DQWs͒. We observed nutation of the population between the resonantly coupled exciton states of DQWs, where the coupling strength of the near-field interaction decreased exponentially as the separation increased.To evaluate the energy transfer, three samples were prepared ͓Fig. 1͑a͔͒: ͑1͒ single-quantum-well structures ͑SQWs͒ with a well-layer thickness of L w = 2.0 nm ͑SQWs͒, ͑2͒ DQWs with L w = 3.5 nm with 6 nm separation ͑1-DQWs͒, and ͑3͒ three pairs of DQWs with L w = 2.0 nm with different separations ͑3, 6, and 10 nm͒, where each DQW was separated by 30 nm ͑3-DQWs͒. These thicknesses were determined by the transmission electron microscopy ͑TEM͒ measurement. ZnO / ZnMgO quantum-well structures ͑QWs͒ were fabricated on the ends of ZnO nanorods with a mean diameter of 80 nm using catalyst-free metal organic vapor phase epitaxy. 10 The average concentration of Mg in the ZnMgO layers used in this study was determined to be 20 at. %.The far-field photoluminescence ͑PL͒ spectra were obtained using a He-Cd laser ͑ = 325 nm͒ before detection using near-field spectroscopy. The near-field photoluminescence ͑NFPL͒ spectra were obtained using a He-Cd laser ͑ = 325 nm͒, collected with a fiber probe with an aperture diameter of 30 nm, and detected using a cooled chargecoupled device through a monochromator. Blueshifted PL peaks were observed at 3.499͑I S ͒, 3.429͑I 1D ͒, and 3.467 ͑I 3D ͒ eV in the far-and near-field PL spectra ͓Fig. 2͑a͔͒. We believe that these peaks originated from the respective ZnO QWs because their energies are comparable to the predicted ZnO well-layer thicknesses of 1.7͑I S ͒, 3.4͑I 1D ͒, and 2.2 ͑I 3D ͒ nm, respectively, calculated using the finite square-well potential of the quantum confinement effect in ZnO SQWs. 10 To confirm the near-field energy trans...

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confidence: 99%

Nanophotonic switch using ZnO nanorod double-quantum-well structures

Yatsui¹,

Sangu²,

Kawazoe³

et al. 2007

Applied Physics Letters

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“…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][3][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.…”

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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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“…9(c), which now concerns the threshold. The SE energy is 100 meV lower than that of the absorption peak [28,39]. We discuss the energy difference between the SE and absorption peaks.…”

Section: Nonlinear Optical Propertiesmentioning

confidence: 98%

“…These must be overcome for an optoelectrical device to be operable at RT [27]. The XRD patterns of the MQWs on SCAM showed Bragg diffraction peaks and clear intensity oscillations due to Laue patterns corresponding to the layer thickness [28]. This indicates a high crystallinity and a high degree of thickness homogeneity.…”

Section: Linear Optical Propertiesmentioning

confidence: 99%

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Optical properties of ZnO-based quantum structures

Makino

2005

Superlattices and Microstructures

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The optical properties of ZnO quantum wells, which have potential application of short-wavelength semiconductor laser utilizing a high-density excitonic effect, were investigated. Stimulated emission of excitons was observed at temperatures well above room temperature due to the adoption of the lattice-matched substrates. The mechanism of stimulated emission from ZnO quantum wells is discussed in this paper.

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Room-temperature stimulated emission of excitons in ZnO/(Mg, Zn)O superlattices

Cited by 255 publications

References 17 publications

Nanophotonic switch using ZnO nanorod double-quantum-well structures

Nanophotonic switch using ZnO nanorod double-quantum-well structures

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

Optical properties of ZnO-based quantum structures

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