Enhanced quality of epitaxial AlN thin films on 6H-SiC by ultra-high-vacuum ion-assisted reactive dc magnetron sputter deposition

Epitaxial AlN thin films have been grown on 6H-SiC substrates by ultra-high -vacuum (UHV) ion-assisted reactive dc magnetron sputtering. The low-energy ion-assisted growth (E-i = 17-27 eV) results in an increasing surface mobi lity, promoting domain-boundary annihilation and epitaxial growth. Domain w idths increased from 42 to 135 nm and strained-layer epitaxy was observed i n this energy range. For E-i> 52 eV, an amorphous interfacial layer of AlN was formed on the SiC, which inhibited epitaxial growth. Using UHV conditio n and very pure nitrogen sputtering gas yielded reduced impurity levels in the films (O: 3.5 x 10(18) cm(-3)). Analysis techniques used in this study are in situ reflection high-energy electron diffraction, secondary-ion-mass spectroscopy, atomic-force microscopy, x-ray diffraction, and cross-sectio n high-resolution electron microscopy. (C) 2000 American Institute of Physi cs. [S0003-6951(00)01802-7].