X-ray absorption, glancing-angle reflectivity, and theoretical study of the N K- and Ga M{sub 2,3}-edge spectra in GaN
- Department of Physics, Case Western Reserve University, Cleveland, Ohio 44106-7079 (United States)
- Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720 (United States)
- Naval Research Laboratory, Washington, D.C. 20375 (United States)
- UNIPRESS, Polish Academy of Sciences, 01-142 Warszawa (Poland)
- Applied Physics Laboratory, Johns Hopkins University, Baltimore, Maryland 20723 (United States)
A comprehensive study of the nitrogen K edge and gallium M{sub 2,3} edge in gallium nitride is presented. Results of two different experimental techniques, x-ray absorption by total photocurrent measurements and glancing-angle x-ray reflectivity, are compared with each other. First-principles calculations of the (polarization averaged) dielectric response {epsilon}{sub 2}({omega}) contributions from the relevant core-level to conduction-band transitions and derived spectral functions are used to interpret the data. These calculations are based on the local density approximation (LDA) and use a muffin-tin orbital basis for the band structure and matrix elements. The angular dependence of the x-ray reflectivity is studied and shown to be in good agreement with the theoretical predictions based on Fresnel theory and the magnitude of the calculated x-ray optical response functions. The main peaks in the calculated and measured spectra are compared with those in the relevant partial density of conduction-band states. Assignments are made to particular band transitions and corrections to the LDA are discussed. From the analysis of the N K and Ga M{sub 2,3} edges the latter are found to be essentially constant up to {approximately}10 eV above the conduction-band minimum. The differences in spectral shape found between the various measurements were shown to be a result of polarization dependence. Since the c axis in all the measurements was normal to the sample surface, p-polarized radiation at glancing angles corresponds to {bold E}{parallel}{bold c} while s polarization corresponds to {bold E}{perpendicular}{bold c} at all incident angles. Thus, this polarization dependence is a result of the intrinsic anisotropy of the wurtzite structure. Spectra on powders which provide an average of both polarizations as well as separate measurements of reflectivity with s polarization and p polarization were used. {copyright} {ital 1997} {ital The American Physical Society}
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 489285
- Journal Information:
- Physical Review, B: Condensed Matter, Vol. 55, Issue 4; Other Information: PBD: Jan 1997
- Country of Publication:
- United States
- Language:
- English
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