Characterization of GaN/Si(111) heteroepitaxy with variation of thickness grown by using Al _xGa _1-xN superlattice intermediate layer

We have studied the growth of Al _0.2Ga _0.8N/GaN superlattices as an intermediate layer between GaN epitaxal layer and Si substrate in order to control the tensile stress induced by cooling after growth. This Al _0.2Ga _0.8N/GaN superlattice is used for avoiding the abrupt change in thermal expansion coefficient between the GaN epitaxial layer and Si substrate as well as for improving the structural and optical qualities of the GaN layer. We report on characterization of various thickness changes of GaN/Si(111) epitaxial layer grown by metalorganic chemical vapor deposition (MOCVD). We have studied the effect of various thickness changes of GaN epitaxial layer from 0.5 to 1.2 μm, and, we have obtained a crack free GaN/Si(111) epitaxial layer with various thicknesses ranging from 0.5 to 1.0 μm and the best characteristics of the GaN epitaxial layer at 1.0 μm. Photoluminescence (PL) spectra at room temperature of the GaN/Si(111) epitaxial layer grown on the superlattice showed a sharp band edge emission peak at 366.2 nm with full width at half maximum (FWHM) of 63.9 meV. The average RMS by atomic force microscope (AFM) was 0.775 nm. FWHM of double-crystal X-ray diffractometer (DCXRD) rocking curve obtained for the (0002) diffraction was 886 arcsec. It was found that the characterization of the GaN/Si(111) with A _l.2Ga _0.8N/GaN superlattice was still worse than that on GaN/sapphire, due to the existence of the intrinsic tensile stress caused by GaN grain boundaries.