Growth of atomically smooth AlN films with a 5:4 coincidence interface on Si(111) by MBE

摘要

Epitaxial aluminum nitride AlN (0001) thin films have been grown by plasma-assisted molecular beam epitaxy (PA-MBE) on Si(111). The influence of the composition of the nitrogen plasma on the crystal quality, as judged by X-ray diffractometry (XRD) and atomic force microscopy (AFM), has been investigated. Under an Al/N vapor phase ratio close to unity atomically smooth AlN films have been grown at 850 deg C substrate temperature with maximum growth rates of 2.5 nm min~(-1). A 3~(1/2)x 3~(1/2) and a more Al-rich 2 x6-surface reconstruction have been observed. Transmission electron microscopy (TEM) investigations show that these films are homogeneous 2H-AlN single crystals. Their defect structure consists of threading dislocations mostly. The hetero-interface is abrupt and flat. Processed high-resolution (HR) TEM images demonstrate a 4 x d_(Si(T10)) to 5 x d_(AlN(2110)) coincidence between substrate and epilayer. The XRD FWHM of the (0002)-diffraction peak of 0.5 mu m AlN is 0.06 deg in the omega /2 theta scan and 0.32 deg in the omega scan. Phonon modes of AlN have been detected by Raman and infra-red spectroscopy.