LATTICE-CONSTANTS, THERMAL-EXPANSION AND COMPRESSIBILITY OF GALLIUM NITRIDE

High-resolution x-ray diffraction measurements can be performed at variable temperatures and pressures. The usefulness of such experiments is shown when taking gallium nitride, which is a wide-band semiconductor, as an example. The GaN samples were grown at high pressures (bulk crystals) and as epitaxial layers on silicon carbide and sapphire. The x-ray examinations were done at temperatures of 293-750 K and-at pressures of up to 8 kbar. The results served for an evaluation of the basic physical properties of gallium nitride; namely lattice constants, thermal expansion and compressibility. The comparison of monocrystals with epitaxial layers grown on highly mismatched substrates provided important information about the influence of the substrate on the crystallographic perfection of the layers.