Improved surface morphology of flow‐modulated MOVPE grown AlN on sapphire using thin medium‐temperature AlN buffer layer

Abstract

AbstractHigh‐temperature (HT) AlN films were grown on (0001) sapphire by low‐pressure flow‐modulated (FM) metal organic vapor phase epitaxy (MOVPE) with and without inserting a thin medium‐temperature (MT) AlN layer. To suppress parasitic reactions between the sources of trimethylaluminum (TMA) and ammonia (NH3), TMA and NH3 was introduced to the reactor of MOVPE by alternating supply way. Surface morphology and crystalline quality were characterized by a scanning electronic microscopy (SEM), atomic force microscopy (AFM) and X‐ray rocking curve (XRC) measurements of (0002) and (10‐12) diffractions. The AFM and SEM measurements indicated that the thin MT‐AlN layer had a strong influence on the surface morphology of the HT‐AlN films. The surface morphology became quite smooth by inserting the thin MT‐AlN layer and surface RMS roughness values were 0.84nm and 13.4nm for the HT‐AlN films with and without inserting the thin MT‐AlN buffer layer, respectively. By etching the samples in aqueous KOH solution, it was found that the polarity of AlN films was different, the HT‐AlN film with the thin MT‐AlN layer could not be etched, indicating that the film had an Al‐polar surface; however, the film without the MT‐AlN layer was etched, which was explained that that film had a N‐ or mixed polar surface. The mechanism for the origin of the different polarity of HT‐AlN with and without the thin MT‐AlN layer was proposed and discussed in detail. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)