SummaryThin films incorporating GaN, InGaN and AlGaN are presently arousing considerable excitement because of their suitability for UV and visible light-emitting diodes and laser diodes. However, because of the lattice mismatch between presently used substrates and epitaxial nitride thin films, the films are of variable quality.In this paper we describe our preliminary studies of nitride thin films using electron backscattered diffraction (EBSD). We show that the EBSD technique may be used to reveal the relative orientation of an epitaxial thin film with respect to its substrate (a 90 ° rotation between a GaN epitaxial thin film and its sapphire substrate is observed) and to determine its tilt (a GaN thin film was found to be tilted by 13 ± 1 ° towards [10 0] GaN ), where the tilt is due to the inclination of the sapphire substrate (cut off-axis by 10 ° from (0001) sapphire towards (10 0) sapphire ). We compare EBSD patterns obtained from As-doped GaN films grown by plasma-assisted molecular beam epitaxy (PA-MBE) with low and high As 4 flux, respectively. Higher As 4 flux results in sharper, better defined patterns, this observation is consistent with the improved surface morphology observed in AFM studies. Finally, we show that more detail can be discerned in EBSD patterns from GaN thin films when samples are cooled.
The acquisition of electron backscattered diffraction (EBSD) (or Kikuchi diffraction) patterns in the scanning electron microscope is proving to be a useful technique with which to probe the structural properties of nitride thin films. In this paper we show that if a sample is cooled the patterns improve dramatically, an increase in intensity of the Kikuchi lines and a decrease in the intensity of the diffuse background is observed. Kikuchi lines from higher order planes become visible and the HOLZ rings become better defined. Such cooled patterns yield more information on the sample, particularly on non-centrosymmetric planes, from which the polarity of the nitride thin film under investigation may be deduced.Introduction The acquisition of electron backscattered diffraction (EBSD) (or Kikuchi diffraction) patterns in the scanning electron microscope is a very powerful method for the microstructural characterisation of crystalline materials. EBSD is at present predominantly used in metallurgy for the measurement of texture, i.e., the mapping of the orientation of individual grains in polycrystalline samples [1], and to identify different crystalline phases. However, Wilkinson [2] and Troost et al. [3] applied EBSD to the measurement of strain in SiGe epilayers while Baba-Kishi [4] has used EBSD to investigate crystallographic polarity of non-centrosymmetric structures. These results strongly suggest that EBSD may be a useful technique to apply to the characterisation of nitride thin films.In previous work [5] we have used EBSD to reveal the relative orientation of a nitride thin film with respect to its substrate; determine the tilt of a GaN thin film; detect improved surface quality in As-doped GaN films grown under high As 4 flux; and observe more detail in EBSD patterns from cooled GaN thin films. In this paper we show that EBSD patterns obtained from cooled GaN thin films can provide information on non-centrosymmetric planes, from which the polarity of the nitride thin film under investigation may be deduced.
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