Growth of crack-free GaN on Si(1Â 1Â 1) with graded AlGaN buffer layers

Hexagonal GaN films on Si(1 1 1) substrates have been grown by metalorganic vapor phase epitaxy (MOVPE). High-temperature AlN buffers provided a reliable diffusion barrier to avoid meltback etching. By introducing a thick, graded AlGaN buffer layer, the critical thickness for cracking has been increased to at least 2μm. The films have been characterized by optical microscopy, transmission electron microscopy (TEM) and X-ray diffraction.