Electronic structure of aluminum nitride: Theory and experiment
| Autor: | Roger H. French, G. A. Slack, Y. N. Xu, Wai-Yim Ching, S. Loughin |
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| Rok vydání: | 1993 |
| Předmět: | |
| Zdroj: | Applied Physics Letters. 63:1182-1184 |
| ISSN: | 1077-3118 0003-6951 |
| DOI: | 10.1063/1.109764 |
| Popis: | Recent efforts to develop electronic.,’ optical, and electro-optical’ -” components and applications based on wide band-gap III-V materials have generated considerable practical interest in the electronic structure of AlN. While a number of theoretical calculations5m10 of the band structure exist, the experimental work”-‘” available for comparison has been limited in either energy range or energy resolution. Extant experimental studies are mostly on thin films due to the difficulty of growing high-purity bulk crystals of 41N. Aside from techuological applications, the electronic structure of AlN is also of fundamental interest. Calculation of the electronic structure of ceramics is a developing area of theoretical physics and the nitrides are of particular importance because the bonding is more covalent than in the oxides. Experimental information about the electronic structure of AlN provides insight as to how theoretical models based on oxides should be adapted to covalent ceramics. Quantitative comparison of theory and experiment affords the best tool for gaining this insight. To this end, we present our results in terms of analytical critical point models of the interband transition strength, J,, , for both a first principles calculation and a vacuum ultraviolet (VW) optical measurement. Our method emphasizes the relationship among critical points grouping them into sets representative of transitions between pairs of bands, while other recent work” emphasizes individual critical points. A single crystal (W201), with a thermal conductivity of 275 W m -’ K-r grown by a modified Bridgman technique,r6 was studied. The oxygen content of the single crystal was 3GO ppm, as previously reported.‘” Polishing with diamond powders suspended in high-purity dry kerosene yields an oxide-free surface for reRectance measurements. Oxidized surfaces give spurious results and were avoided by nonaqueous polishing. The polished face of the single crystal was near normal to the c axis. The VIJV reflectance spectra were obtained with a laser plasma sourced VUV spectrophotometer, described elsewhere.9 Above the band gap at 6.2 eV, t.he spectra show two main features. A sharp peak appears at about 9 eV and a smaller, somewhat brozder peak appears at about l&15 eV. A small feature also appears at about 35 eV. Small features below the band gap are due to vacancies. The single crystal response was found to be representative of commercial polycrystalline substrates also studied.” The spectrum was adjustedd, consistent with an index of jz[ 1.25 eV] = 2.1 A Kramers-Kriinig (KK) analysi?” recovered the phase information, S[h,\r], and permitted calculation of other optical properties,” including the complex dielectric function shown in Fig. 1. The energy band structure of AlN was calculated from first principles, using the orthogonalized linear combination of atomic orbitals (OL.CAOj method with the local density approximation (LDA |
| Databáze: | OpenAIRE |
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