Heteroepitaxial growth of GaN on Si substrate coated with a thin flat SiC buffer layer

High quality cubic and hexagonal GaN films were grown on Si(001) and Si(111) coated with a thin flat SiC buffer layer. The thicknesses of cubic SiC(001) and SiC(111) buffer layers were about 2.5 mn. The thin flat SiC layer was an effective buffer layer for epitaxial GaN growth. The reduction in SiC surface roughness reduced the defect density in GaN films. Under N-rich growth condition, both the cubic (beta -GaN) and hexagonal GaN (alpha -GaN) films showed statistical roughening of the surface and a characteristic columnar structure. Under Ga-rich condition, flat and better crystal quality GaN films were obtained. For beta -GaN film, the compressive stress caused by the lattice mismatch between GaN and SiC was essentially relaxed within tens of nanometers after film growth. The strong yellow-band luminescence found only in alpha -GaN may be related to screw and/or mixed dislocations in the GAN grains.