The effects of growth temperature of AlN buffer layers on a-plane GaN grown on r-plane sapphire by MOCVD

To grow high quality a-GaN films on r-sapphire substrates, it is essential to optimize the buffer layers (BLs) growth parameters such as temperature, thickness, and V/III ratio. In this work, we investigated the effects of growth temperature for AlN BLs on the surface morphology and the crystal quality of a-GaN films. The films studied here were grown epitaxially by metalorganic chemical-vapor deposition (MOCVD) with different AlN BLs grown at 690 deg. C, 720 deg. C, 750 deg. C, respectively. The properties of a-GaN films were comprehensively studied via high resolution x-ray diffraction (HRXRD), optical microscope (OM) and atomic force microscope (AFM). It is found that the crystal quality and the surface morphology of a-GaN films have been remarkably affected by the growth temperature of the AlN BLs. At the optimum AlN BLs growth temperature of 720 deg. C, the a-GaN films have the best crystal quality - and the smoothest surface morphology with the (1120) HRXRD FWHM of 864 arcsec and the root mean square (RMS) surface roughness of 1.2 nm, respectively.