GROWTH OF GALLIUM NITRIDE THIN-FILMS BY LIQUID-TARGET PULSED-LASER DEPOSITION

Gallium nitride (GaN) thin films have been grown on several kinds of s ubstrates (fused silica, single crystal silicon, and sapphire) by liqu id-target pulsed laser deposition at substrate temperature of 600 degr ees C and in the presence of ammonia (NH3) gas. X-ray diffraction, sca nning electron microscopy, tunneling electron microscopy, Rutherford b ackscattering (RES), and UV/VIS spectrometry were used to characterize the as-grown GaN films. It is shown that c-axis oriented GaN films ca n be formed if a thin zinc oxide (ZnO) buffer layer was first grown on the virgin substrate. Without the buffer layer the GaN films were fou nd to be polycrystalline with randomly oriented grains. Once the ZnO b uffer layer was used, the GaN films immediately grew in a columnar str ucture with its c-axis normal to the surface of the film. RES data hav e shown that the obtained films are stoichiometric GaN. It was also fo und that the surface morphology and optical transparency of the GaN fi lms were greatly improved by the ZnO buffer layer. (C) 1997 American V acuum Society.