III-V nitrides (AlN, GaN and InN) form one of the most intensively studied families of semiconductors, due to their potential wide applications in short-wave optoelectronics. The lattice mismatch and differences in thermal expansion coefficient values of the layer and of the substrate result in the occurrence of strain in the layers. As the physical properties of the layer are strain-dependent, the knowledge of the thermal expansion of the IIIN layer material is of high importance. Detailed studies of the a and c lattice parameters in a broad temperature range are expected to be useful in development of short-wave optoelectronic devices.
Thermal expansion measurements require collecting of a diffraction patterns at a large number of temperature points. This task can be performed with the use of synchrotron radiation. The X-ray diffraction measurements using Debye-Scherrer geometry were carried out at a powder diffractometer (B2 beamline, HASYLAB/DESY) equipped with a He-closed-cycle cryostat and a furnace. In the low temperature experiments, the temperature was determined by a silicon diode while for high temperatures a NaCl internal standard was applied.
The dependence of a and c on temperature was studied in a broad range 11<T<1173 K. The results are consistent with previously collected (for limited T intervals) data [1-4]. The c/a ratio shows a weak tendency to decrease with temperature. This behavior is similar to that for InN reported in . The free positional parameter, u, is found to be practically independent on T.
1. W. Paszkowicz et al., in: "Synchrotron Radiation Studies of Materials", Eds.: M. Lefeld-Sosnowska, J. Gronkowski, (Warsaw, 2000), pp. 183.
2. R.R. Reeber, K. Wang, J. Mater. Res. 15 (2000) 40.
3. M. Leszczynski et al., Acta Phys. Polon. A90 (1996) 887.
4. V. Kirchner et al., Appl. Phys. Lett. 77 (2000) 1434.
5. W. Paszkowicz, R. Cerny, S. Krukowski, Powder Diffrac. 18 (2003), in print.