Emission from the higher-order excitons in ZnO films grown by laser molecular-beam epitaxy

Tsukazaki, Atsushi; Ohtomo, A.; Kawasaki, Masashi; Makino, T.; Chia, C. H.; Segawa, Y.; Koinuma, Hideomi

doi:10.1063/1.1748847

Cited by 37 publications

(22 citation statements)

References 24 publications

(22 reference statements)

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“…Here, the energy spacing of 47 meV of the peak at 3.423 eV from the FX ðn¼1Þ A at 3.376 eV matches exactly 3/4 of the exciton binding energy in ZnO. Therefore, the transition at 3.423 eV, also reported in the literature, [14][15][16]19,20 is attributed to the (n ¼ 2) state of the A-exciton. A magnification of the (n ¼ 2) spectrum is shown enlarged on a linear scale in the inset of Fig.…”

supporting

confidence: 84%

“…15,16 In this letter, we study the dynamics of the intraexcitonic processes by means of ultrafast emission spectroscopy with sub-picosecond time resolution. We apply a rateequation model to analyze the various relaxation channels and to investigate the influence of temperature and excitation density.…”

mentioning

confidence: 99%

“…These observations are confirmed by the temperature dependence of the (n ¼ 2) emission found in the literature. 16 The extracted (n ¼ 2) to (n ¼ 1) relaxation times are shown in Figs. 4(a) and 4(b) as a function of excitation density and temperature, respectively.…”

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Intra-excitonic relaxation dynamics in ZnO

Chernikov

Koch

Laumer

et al. 2011

Applied Physics Letters

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The temperature and carrier-density dependent excitonic relaxation in bulk ZnO is studied by means of time-resolved photoluminescence. A rate-equation model is used to analyze the population dynamics and the transitions between different exciton states. Intra-excitonic (n ¼ 1) to (n ¼ 2) relaxation is clearly identified at low excitation densities and lattice temperatures with a characteristic time constant of 6 6 0.5 ps. V C 2011 American Institute of Physics.[doi:10.1063/1.3668102] Over the last decades, ZnO has attracted much interest in the scientific community mainly due to its potential application for optoelectronic devices in the ultraviolet (UV) spectral regime. In addition, properties associated with the large exciton binding energy of 60 meV and the strong electron-phonon coupling are of fundamental interest. Recently, high quality ZnO samples have become available due to improved growth methods.2-6 These advances allow for accurate studies of the electro-optical properties of the material and are important steps towards the realization of ZnO-based technology. Significant research effort has been directed towards the growth and applications of quantum well structures, 7,8 ternary ZnO-based compounds, [9][10][11][12] electron-phonon interaction, 13 and exciton-polaritons.14 Even steady-state investigations of the excited excitonic states have become possible. 15,16 In this letter, we study the dynamics of the intraexcitonic processes by means of ultrafast emission spectroscopy with sub-picosecond time resolution. We apply a rateequation model to analyze the various relaxation channels and to investigate the influence of temperature and excitation density.All time-resolved photoluminescence (PL) measurements are performed using a streak-camera setup 12 yielding spectral and time resolutions of 0.15 nm and 500 fs, respectively; a pulsed 100 fs-Ti:sapphire laser is used as an excitation source. The investigated sample is a 300 nm thick c-plane ZnO layer grown by plasma-assisted molecular beam epitaxy.11 The emission signal is collected normally to the sample surface in reflection geometry. Structural analysis by high resolution x-ray diffraction was carried out and the lattice parameters were extracted from reciprocal space maps recorded at the asymmetric (20.5) reflex. The c-lattice parameter was determined to (5.2046 6 0.001) and the a-lattice parameter to (3.2515 6 0.001). Comparison to data reported in literature reveals that the present ZnO layer can be considered as unstrained. transition is attributed to the luminescence of the free B-excitons. Also, an additional, distinct emission peak is found at 3.423 eV. In a simplified picture, the excitonic level scheme resembles the energy structure of a hydrogen atom.1 In this case, the energy of an excited states is proportional to E b n 2 , where E b is the binding energy and n is the quantum number of the corresponding state. Thus, the energy of the first excited state with (n ¼ 2) is 1/4 E b and the separation between the (n ¼ 1) and (n ¼ 2) states eq...

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Intra-excitonic relaxation dynamics in ZnO

Chernikov

Koch

Laumer

et al. 2011

Applied Physics Letters

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“…115,116 These values were record breaking even if compared with bulk single crystals of ZnO. The keys are to employ lattice-matched ScAlMgO 4 substrates, 117 to insert lattice-mismatch engineered and ultrasmooth ZnO buffer layer, 118,119 and to employ laser heating of substrate for clean and ultrahigh temperature above 1000°C. 13 The growth temperature (T g ) optimization was carried out by temperature gradient shown in Figure 4c.…”

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confidence: 99%

Exploration of Electronic Functionalities in Metal Oxides by Combinatorial Lattice Engineering

Kawasaki

2013

Bulletin of the Chemical Society of Japan

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A review is given for our originally-developed thin film technology, "combinatorial lattice engineering." This is extended from a conventional pulsed laser deposition, where the surface of a sintered oxide tablet (target) is irradiated with focused laser pulses and the evaporated precursors are condensed on a heated substrate to grow single crystalline thin films. By this method, it has become possible to concurrently synthesize many oxide thin films on a substrate at different locations (segments) with such diversities as composition, growth conditions, and the sequence of heterostructures. By inserting a masking system between the target and substrate and computer controlling the mask motion as well as target switching, one can integrate many oxide thin film segments on the substrate. Starting from the background of and demand for this technology as well as the advancement of the key ingredient technology, i.e., atomically regulated epitaxial growth of oxide thin films, the concept and examples of this combinatorial lattice engineering are introduced highlighting the representative demonstration on magnetic, photonic, and electronic functionalities, especially emphasizing the benefit of this combinatorial technology. In addition, further progress of device physics triggered by the combinatorial discoveries are introduced, for example, electric field control of magnetism, bright ultraviolet light emitting devices, and quantum effects in oxide semiconductors.

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“…Nonequilibrium growth conditions vary with the preparing technique, such as pulsed laser deposition (PLD), 13,14 sputtering, 15 metalorganic vapor phase epitaxy (MOVPE), 16 and molecular beam epitaxy (MBE), 17 leading to a different Mg saturation concentration. Accordingly, it is worth applying various preparation methods to explore the Mg saturation content and thermal stability of the MgZnO alloys in order to better understand this material.…”

Section: +mentioning

confidence: 99%

Composition Dependence on Structural and Optical Properties of Mg_xZn_1-xO Thin Films Prepared by Sol-Gel Method

Kim¹,

Noh²,

Yim³

et al. 2011

Bulletin of the Korean Chemical Society

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The Mg x Zn 1-x O thin films with the various content ratio ranging from 0 to 0.4 were prepared by sol-gel spincoating method. To investigate the effects of content ratio on the structural and optical properties of the Mg x Zn 1-x O thin films, scanning electron microscopy (SEM), X-ray diffraction (XRD), and photoluminescence (PL) were carried out. With increase in the content ratio, the grain size of the Mg x Zn 1-x O thin films was increased, however, at the content ratio above 0.2, MgO particles with cubic structure were formed on the surface of the Mg x Zn 1-x O thin films, indicating that the Mg content exceeded its solubility limit in the thin films. The residual stress of the Mg x Zn 1-x O thin films is increased with increase in the Mg mole fraction. In the PL investigations, the bandgap and the activation energy of the Mg x Zn 1-x O thin films was increased with the Mg mole fraction.

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Emission from the higher-order excitons in ZnO films grown by laser molecular-beam epitaxy

Cited by 37 publications

References 24 publications

Intra-excitonic relaxation dynamics in ZnO

Intra-excitonic relaxation dynamics in ZnO

Exploration of Electronic Functionalities in Metal Oxides by Combinatorial Lattice Engineering

Composition Dependence on Structural and Optical Properties of Mg_xZn_1-xO Thin Films Prepared by Sol-Gel Method

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Emission from the higher-order excitons in ZnO films grown by laser molecular-beam epitaxy

Cited by 37 publications

References 24 publications

Intra-excitonic relaxation dynamics in ZnO

Intra-excitonic relaxation dynamics in ZnO

Exploration of Electronic Functionalities in Metal Oxides by Combinatorial Lattice Engineering

Composition Dependence on Structural and Optical Properties of MgxZn1-xO Thin Films Prepared by Sol-Gel Method

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Composition Dependence on Structural and Optical Properties of Mg_xZn_1-xO Thin Films Prepared by Sol-Gel Method