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Characterisation of nitride thin films by EBSD

Trager-Cowan, C. and Sweeney, F. and Hastie, J. and Manson-Smith, S.K. and Cowan, D.A. and McColl, D. and Mohammed, A. and O'Donnell, K.P. and Zubia, D. and Hersee, S.D. and Foxon, C.T. and Harrison, I. and Novikov, S.V. (2002) Characterisation of nitride thin films by EBSD. Journal of Microscopy, 205 (3). pp. 226-230. ISSN 0022-2720

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Abstract

Thin 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.