ORALS

High resolution X-ray diffractometry is the primary structural method used in the investigations of epitaxial layers and structures. In high resolution configuration a 4-bounce Ge(220) Bartels monochromator gives an incidence beam divergence of 12 arcsec. In the diffracted beam path, open detector configuration is used for rocking curves (RC) measurements or triple-axis analyser crystal before the detector is used for reciprocal lattice maps (RLM) measurements. Such configurations allow investigations of the single crystals semiconductor structures including: low-dimensional quantum well (QW), quantum dots (QDs) of lasers, LEDs and solar cells structures. The analysis of the results such as RC and RLM allow determination of the basic parameters of the structure: thickness and composition of the layers, degree of relaxation, lattice parameters, size of crystalline blocks and mosaicity of the highly mismatched structures but also dislocations density and strain in the epitaxial layers. In such analysis the main problem is the measurement of planes perpendicular to the sample surface. In standard XRD configuration it is practically impossible to measure such planes for such highly oriented samples. In order to avoid this problem, planes with a large inclination angle, (e.g. over 60 deg) are investigated using the skew geometry. The application of measurements carried out from the edge of the sample allows analysis of such structures, above all, spatial separation of the effects shown in the investigation results. In particular, it allows independently determination of the lattice parameter perpendicular to the growth direction, separation of tilt and twist mosaicity [1], calculation of the edge dislocations density [2] or residual strains in the structure. Furthermore, such type of measurements reveals the difference in lattice parameters of the specific layers [3], which are not always visible with conventional measurements performed from the surface of the sample. This type of measurements were developed in Structural Research Laboratory in Wroclaw University of Science and Technology and has been used in the analysis of epitaxial structures - mainly mismatched III-N materials like (Ga, Al)N, low dimensional structures (QW and QDs) of the III-V materials but also (Zn,Cd)Te superlattices.

References:
[1] J. Serafinczuk, Cryst. Res. Technol. 51 (2016) 276–281
[2] J. Serafinczuk, K. Moszak, Ł. Pawlaczyk, W. Olszewski, D. Pucicki, R. Kudrawiec, D. Hommel, J. Alloys Compd. 825 (2020) 153838
[3] R. Kucharski, M Zajac, A Puchalski, T Sochacki, M Bockowski, JL Weyher, M. Iwinska, J Serafinczuk, R. Kudrawiec, Z. Siemiątkowski, Journal of Crystal Growth 427(2015) 1-6