Diffraction

Abstract

—The structure of short(cid:2)period hexagonal GaN/AlN superlattices (SLs) has been investigated by X(cid:2) ray diffraction. The samples have been grown by metalorganic vapor(cid:2)phase epitaxy (MOVPE) in a horizontal reactor at a temperature of 1050°C on (0001)Al 2 O 3 substrates using GaN and AlN buffer layers. The SL period changes from 2 to 6 nm, and the thickness of the structure varies in a range from 0.3 to 1 μ m. The com(cid:2) plex of X(cid:2)ray diffraction techniques includes a measurement of θ –2 θ rocking curves of symmetric Bragg reflection, the construction of intensity maps for asymmetric reflections, a measurement and analysis of peak broadenings in different diffraction geometries, a precise measurement of lattice parameters, and the deter(cid:2) mination of radii of curvature. The thickness and strain of separate SL layers are determined by measuring the θ –2 θ rocking curves subsequent simulation. It is shown that most SL samples are completely relaxed as a whole. At the same time, relaxation is absent between sublayers, which is why strains in the AlN and GaN sublayers (on the order of 1.2 × 10 –2 ) have different signs. An analysis of diffraction peak half(cid:2)widths allows us to determine the densities of individual sets of dislocations and observe their change from buffer layers to SLs.