Pressure dependence of the lattice dynamics of ZnO: An<i>ab initio</i>approach

Serrano, Joaquim Rigola; Romero, A. H.; Manjón, F. J.; Lauck, R.; Cardona, M.; Rubio, Ángel

doi:10.1103/physrevb.69.094306

Cited by 421 publications

(305 citation statements)

References 75 publications

(98 reference statements)

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“…The positive thermal-expansion contribution to the Zn-related term is a result of the negative average Grüneisen parameter for acoustic phonons. 30 As was already mentioned in Refs. 17 and 20, the contribution of the oxygen vibrations to the gap renormalization at T = 0 is about five times larger than that of the zinc vibrations.…”

Section: Band Gap ͑Sample͒supporting

confidence: 64%

Effect of temperature on isotopic mass dependence of excitonic band gaps in semiconductors: ZnO

Alawadhi

Tsoi

et al. 2007

Phys. Rev. B

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The temperature dependence of the A, B, and C excitons of ZnO, observed in modulated reflectivity spectra of 68 Zn 18 O and nat Zn nat O in the range 10-400 K, reveal the superposition of band-gap renormalization originating in electron-phonon interaction and volume changes associated with thermal expansion and ͑or͒ isotopic composition in combination with anharmonicity. At low temperatures, the A, B, and C excitons in natural ZnO reach limiting values depressed from their values for the infinitely massive isotopes ͑the latter are free from electron-phonon interaction and anharmonicity͒. The C excitons of 68 Zn 18 O and nat Zn nat O converge with increasing temperature, demonstrating the independence of the band gap from isotopic mass at high temperatures.

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Section: Band Gap ͑Sample͒supporting

confidence: 64%

Effect of temperature on isotopic mass dependence of excitonic band gaps in semiconductors: ZnO

Alawadhi

Tsoi

et al. 2007

Phys. Rev. B

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“…The stronger the confinement the more phonons far from the Γ-point contribute to the Raman scattering. The CdSe bulk phonon dispersion shows an overbending near the Γ-point, which can be found in other hexagonal lattices as well [73,74]. This leads to the observed downshift behavior.…”

Section: Size-dependent Raman Spectramentioning

confidence: 68%

Optical phonons in colloidal CdSe nanorods

Lange

Mohr

Artemyev

et al. 2010

Physica Status Solidi (b)

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Colloidal CdSe nanorods are nanoparticles synthesized in solution. The synthesis allows the growth of CdSe nanorods with well defined diameters and aspect ratios. They have many potential applications in the field of optoelectronics and biotechnology. The nanorods can be epitaxially covered with a graded CdS/ZnS shell of a few monolayers in thickness. The shell leads to an increased quantum efficiency and improved photostability of the nanorods. However, the lattice mismatch between the nanorod core material and the shell material introduces strain into the core lattice. In this work Raman spectroscopy, accompanied by ab-initio calculations, is used to determine the amount of this strain, the exciton-phonon coupling strength in the nanorods and to investigate confinement effects. The longitudinal optical phonons in a nanorod are confined to the nanorod volume. The confinement of a phonon wavefunction leads to a neutralization of the q = 0 rule and the phonon frequency is found to depend on the nanorod diameter. The coupling strength between longitudinal optical phonons and excitons is investigated. It also depends on the nanorod diameter. The total coupling strength is much lower than in bulk material due to a decrease of the influence of the Coulomb interaction in nanoparticles. However, the coupling strength is found to rise for decreasing diameters. This is due to the increasing contributions of higher frequency phonons for smaller nanoparticle sizes. A radial breathing mode with a diameter dependent frequency is deduced from ab-initio calculations and its existence in nanorods is verified experimentally. The diameter-dependence of the modes' frequency can be used to estimate the nanorod diameter from a Raman measurement. In core-shell structures, the coverage of a CdSe nanorod with a ZnS shell leads to a compressive strain of the CdSe core due to the smaller lattice parameter of ZnS compared to CdSe. Ab-initio calculations show that all bonds of the CdSe core are shortened. The bonds in the lateral direction are much more strongly compressed than the bonds parallel to the c-axis. The amount of strain is estimated from the Raman spectra. The compressive nature of the shell decreases for thicker nanorods. The exciton wave function changes with the modified boundary from air to ZnS. This is reflected in a altered exciton-phonon coupling strength and can be monitored in the Raman spectra. ZusammenfassungCdSe Nanorods sind Nanopartikel, die in einer kolloidalen Lösung synthetisiert werden. Für diese existieren viele mögliche Anwendungen im Bereich der Optoelektronik und der Biotechnologie. Der Durchmesser und die Länge der Nanorods lässt sich durch die Syntheseparameter festlegen. Die Nanorods können in eine epitaktische Hülle aus einem Halbleitermaterial mit einer größeren Bandlücke, ZnS, eingebettet werden. Diese Hülle verbessert die optischen Eigenschaften und ermöglicht eine weitere Funktionalisierung der Oberfläche. Der Unterschied der Gitterparameter zwischen ZnS und CdSe führt jedoch zu Verspannung...

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“…The transformation from wurtzite to hexagonal for II-VI and III-IV compounds has already been studied. [9][10][11][12][13][14][15][16] In the above studies, treated compression conditions are basically hydrostatic (isotropic) with the exception of c=a compression 10,14) mentioned later. The hexagonal phase is treated as an intermediate or metastable phase between a wurtzite !…”

Section: )mentioning

confidence: 99%

Electronic and Lattice Properties of Layered Hexagonal Compounds Under Anisotropic Compression: A First-Principles Study

Kobayashi

2005

Mater. Trans.

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We have investigated the wurtzite and hexagonal compounds (w-and h-BN, AlN, ZnO) under various compression conditions using the first-principles molecular dynamics (FPMD) method. Applying anisotropic compression is an important approach for the investigation of novel material properties. We found remarkable changes in the internal parameters u of all calculated wurtzite compounds under uniaxial c-axis compression (P z ) within the symmetry constraint. The internal parameter u of the wurtzite structure increased as the pressure increased and finally became 0.5, resulting in a phase transformation into a hexagonal structure. Transition pressures for BN, AlN and ZnO under c-axis compression are 300-325, 15-20, 5-10 GPa, respectively. The value of the transition pressure of BN (wurtzite ! hexagonal) was found to be significantly higher than those of the other two compounds (AlN, ZnO) in which the crystal structure of BN could be broken under the large uniaxial compression. The changes in the electronic band structure and the lattice properties (lattice constant, c=a ratio, volume of the unit cell) of BN in the wurtzite-to-hexagonal transformation were also quite large and unusual. These results imply that the wurtzite-to-hexagonal transformation of BN is unlikely to occur. In contrast, the changes in the lattice properties of AlN and ZnO were small because of their low transition pressures (5-20). These lower transition pressures are mainly due to larger ionicity of AlN and ZnO.

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Pressure dependence of the lattice dynamics of ZnO: Anab initioapproach

Cited by 421 publications

References 75 publications

Effect of temperature on isotopic mass dependence of excitonic band gaps in semiconductors: ZnO

Effect of temperature on isotopic mass dependence of excitonic band gaps in semiconductors: ZnO

Optical phonons in colloidal CdSe nanorods

Electronic and Lattice Properties of Layered Hexagonal Compounds Under Anisotropic Compression: A First-Principles Study

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