Photon Factory Activity Report 2004 #22 Part B (2005)
Materials Science

11A/2004G306

Characterization of nanotextured AlN thin films by x-ray absorption
near-edge structures
Isao TANAKA1*, Takeo SUGA2, Satoru YOSHIOKA1, and Teruyasu MIZOGUCHI 3
Dept. of Mat. Sci. & Eng., Kyoto University, Yoshida, Sakyo, Kyoto 606-8501, Japan.
2FIFC,Kyoto University, 34-4 Nishihirakicho, Takano, Sakyo, Kyoto 606-8501, Japan.
3
Institute of Eng. Inn., The University of Tokyo, 2-11-16 Yayoi, Bunkyo, Tokyo 113-8656, Japan.
1Introduction
III-V nitrides based light emitting devices have beenmassively used in modern technology. Pulsed-laser
deposition (PLD) is an emerging technique, which hassome advantages compared to other techniques. Basically
PLD can avoid impurity to incorporate into the film.
Microstructure and stoichiometry of the film can becontrolled by deposition parameters such as substratetemperature, deposition rate, atmosphere, laser power, etc.
In the present study, we report a technique toquantitatively characterize nanotexture of the film using
x-ray absorption near-edge structure (XANES) technique.
The method is extremely useful when the crystallite size
is too small or too much faulted/strained to be analyzed
by conventional XRD technique.
Methodology
The thin films were made by PLD using a KrF*
excimer laser(λ = 248 nm, Lambda Physik COMPex205)
with pulse rate of 5 Hz and laser power of 600 mJ (92J/cm ). Sintered AlN compact was used as a target.
Sample was deposited on substrate of c-cut sapphire
without N2 gas backfill.
XANES were obtained at KEK-PF BL-11A by total
electron yield method with 1200 line/mm grating
monochromators. All measurements of XANES spectra
were carried out in vacuum at room temperature.
In order to interpret experimental spectra, firstprinciples orthogonalized linear combination of atomic
orbitals (OLCAO) method was employed [1]. This is aband structure calculation based on the density functional
theory within local density approximation. In thecalculation, the initial state and final state were calculated
separately. A core hole was included in an Al 1s orbital.
Matrix elements of electric dipole transition between theinitial state and final states were rigorously computed
using wave functions of the two states. In order tominimize artificial interactions among core holes underperiodic boundary condition, a large supercell composedof 108 atoms has been adopted.
Results and Discussion
Crystalline quality and texture of the deposited film
was investigated by XRD. The AlN film is epitaxiallygrown on the substrate with the relationship of AlN(1 01̄0) / / Al2O3(1 1 2̄ 0).
The left panel of Fig. 1 shows experimental XANES ofsample in comparison to that of w-AlN powder. Sample

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was mounted in two different geometries with its surface
90° and 50° to the incident x-ray beam. When measured
with the 50°-geometry, XANES of sample is identical to−1
that of w-AlN powder. The angle is close to cos (1/√3)=54.7°, which should provide averaged XANES of all
crystallographic directions [2]. When measured with the90° geometry, however, peaks B2, C, and D2, as denoted inFig. 1(b), remarkably lost their intensity. Given the factthat the sample exhibits a high degree of texturing along
the c axis normal to the substrate, peaks B2, C, and D2
should be ascribed to the XANES components thatappears only when measured with E/ /c condition where
E is the electric field vector and c is the c axis of thehexagonal crystal. The right panel of Fig. 1 showstheoretical XANES with E // c, E⊥c and average
conditions. The averaged theoretical XANES satisfactory
reproduces the spectrum from the w-AlN powder.
Increase in intensity of peaks B2, C, and D2 is evident inthe E // c condition, which is also in good agreement withthe experimental spectra. We can therefore conclude thatthe absence of peaks B2, C, and D2 can be a goodfingerprint to the preferred orientation of c perpendicular
to the film surface.

Fig. 1 Experimental XANES (left) and theoretical XANES
calculated by first-principles OLCAO method (right).

References[1] S. D. Mo and W. Y. Ching, Phys. Rev. B 62, 7901
(2000).
[2] E. Tegeler, Phys. Status Solidi B 84, 561 (1977).
* isao.tanaka@materials.mbox.media.kyoto-u.ac.jp