Structure and lattice dynamics of GaN and AIN ; ab-initio investigations of straines polytypes and superlattices

Due to its band-gap energy, gallium nitride (GaN) is well-suited for light emission in the blue spectral region. By alloying with aluminium and/or indium, an energetical range even wider than the whole visible spectrum can be covered. For electronic devices based on group-III nitrides, the... Ausführliche Beschreibung

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Verfasserangabe: von Jan-Martin Wagner
Körperschaft: Friedrich-Schiller-Universität Jena [Grad-verleihende Institution]
Format: E-Book, Hochschulschrift
Sprache: Deutsch
veröffentlicht: Jena, 2004
Hochschulschriftenvermerk: Jena, Univ., Diss., 2004
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RVK-Klassifikation: 33.72Ähnliche Treffer finden
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Zusammenfassung: Due to its band-gap energy, gallium nitride (GaN) is well-suited for light emission in the blue spectral region. By alloying with aluminium and/or indium, an energetical range even wider than the whole visible spectrum can be covered. For electronic devices based on group-III nitrides, the influence of strain is a non-negligible intrinsic physical effect. An easy way to experimentally evaluate the strain is the monitoring of lattice vibrations via Raman spectroscopy. With experimental data providing a reliable reference for the strain effects not being available, it is desirable to obtain them from a full quantum-mechanical treatment of the material via first-principles calculations. In this work, the strain dependence of the structural and dielectric properties and of the phonon frequencies of the cubic and the hexagonal polytype of GaN and AlN as well as of short-period superlattices are investigated by ab-initio methods. Three types of strain are considered, corresponding to the application of hydrostatic pressure, of an isotropic biaxial stress in the basal plane, and of a uniaxial pressure along the crystal axis. After a careful internal relaxation of the structures for given external stress, the dielectric constant, Born effective charges and phonon frequencies are calculated using density-functional perturbation theory. Since typical structural changes are of the order of one hundredth of the lattice parameters, to resolve these changes to a precision of a few percent the lattice parameters themselves have to be determined to a precision of 1E-4, which indeed can be achieved.
Beschreibung: 1 Online-Ressource (118 Seiten); graph. Darst