GaP layers grown on GaN with and without buffer layers

The growth of GaP layer on GaN with and without buffer layers by metal-organic chemical vapour deposition （MOCVD） has been studied. Results indicate that the GaP low temperature buffer layer can provide a high density of nucleation sites for high temperature （HT） GaP growth. These sites can promote the two-dimensional （2D） growth of HT GaP and reduce the surface roughness. A GaP single crystal layer grown at 680 ℃ is obtained using a 40-nm thick GaP buffer layer. The full-width at half-maximum （FWHM） of the （111） plane of GaP layer, measured by DCXRD, is 560 arcsec. The GaP layer grown on GaN without low temperature GaP buffer layer shows a rougher surface. However, the FWHM of the （111） plane is 408 arcsec, which is the indication of better crystal quality for the GaP layer grown on GaN without a low temperature buffer layer. Because it provides less nucleation sites grown at high growth temperature, the three-dimensional （3D） growth is prolonged. The crystalline quality of GaP is lightly improved when the surface of GaN substrate is pretreated by PH3, while it turned to be polycrystalline when the substrate is pretreated by TEGa.