Growth and characterization of AlN and GaN thin films deposited on Si(111) substrates containing a very thin Al layer

AIN films and GaN films with AIN buffer layers were deposited via metalorganic vapor phase epitaxy on Si(1 1 1) substrates previously exposed to trimethylaluminum for increasing times. Atomic force microscopy (AFM) was used to determine the influence of Al pre-flow time on the nucleation and surface morphology of the AIN and GaN films. When preceded by a 10 second Al pre-flow, AIN films feature an increased and more uniform nucleation density as compared to films deposited without Al pre-flows. Ten second Al pre-flows were also found to result in a reduction of the RMS roughness for 100 nm thick AIN films from 3.6 nm to 1.0 nm. AFM of 0.5 mum thick GaN films deposited on AIN buffers with varying pre-flow times showed reduced roughness and decreased pit density when using Al pre-flows of 10 or 20 seconds. High resolution x-ray diffraction of the GaN films showed a reduction in the average full-width half-maximum (FWHM) of the GaN (00.2) reflection from 1076 arcsec to 914 arcsec when the AIN buffer layer was initiated with a 10 second Al pre-flow. Increasing the pre-flow time to 20 seconds and 30 seconds resulted in average (00.2) FWHM values of 925 aresec and 928 aresec, respectively. Similar behavior of the peak widths was observed for the (30.2) and (10.3) reflections when the pre-flow times were varied from 0 to 30 seconds.