Thin layers formed from III-V nitrides (AlN, GaN and InN, wurtzite structure type) or their solid solutions are components of optoelectronic devices. The structural data of the bulk material are essential in the design of such devices. In the present work, the structural information on three III-V nitrides is obtained from high-quality powder diffraction patterns collected at a laboratory diffractometer.
Fine AlN, GaN and InN powders studied in this paper were prepared at Warsaw University of Technology from high-purity components. Powder diffraction data were collected at a laboratory Bragg-Brentano diffractometer equipped with copper X-ray tube, Soller slits at both, primary and diffracted beams, a focusing incident-beam monochromator and a semiconductor strip detector. The applied instrument allows for acquiring the data with excellent statistics and resolution. The 2theta range was 5-140 deg. During sample mounting, efforts were made for reduction of possible preferred orientation effects.
Phase analysis indicates that there are no impurity phases in the GaN sample. The kind of minorimpurity phases for AlN and InN was identified as aluminium and indium oxides, respectively; the relative intensities of the corresponding strongest diffraction peaks are about 2-3%. Rietveld refinements were performed using the X'Pert Plus refinement program and using the DBWS98.07 program (upgraded version of the program described in [1]) supported by DMPLOT3.48 graphical interface [2]. An example of refined GaN pattern is shown in Fig. 1. Results for Pearson VII and pseudo-Voigt profile functions and several profile-asymmetry models were analysed. The Rp factor for the refined patterns is of the order of 10%. Values of refined lattice parameters and the free positional parameter of nitrogen are consistent with earlier literature data.
1. R.A.Y. Young, A. Sakthivel, T.S. Moss, and C.O. Paiva-Santos, J. Appl. Crystallogr. 28 (1995) 366.
2. H. Marciniak, unpublished (1998). |