Lattice parameters of GaN single crystals, homoepitaxial layers and heteroepitaxial layers on sapphire

摘要

Lattice parameters of gallium nitride weremeasured using diffraction of X-rays produced by the laboratorygenerators and the European Synchrotron Radiation Facility(ESRF). The following samples were examined: (i) bulk singlecrystals grown at high hydrostatic pressure, undoped and Mg-doped, (ii) homoepitaxial layers grown on those crystals, undoped,Mg-doped and Si-doped, (iii) heteroepitaxial layers grown onsapphire, (iv) heteroepitaxial layers on sapphire after high-pressureannealing treatment, (v) heteroepitaxial layers on sapphire afterimplantation and thermal processes. The lattice parameters weremeasured versus free-electron concentration established byphotoluminescence, far-infrared reflectivity and the Hall method. Itis concluded that the main factor causing an increase of the latticeparameters of GaN are free electrons which act via thedeformation potential of the conduction band. For heteroepitaxiallayers, the strains caused by the mismatched substrates arediscussed in terms of the mosaicity of these layers and thermalmismatch with respect to the substrates.