Growth and characterization of wurtzite and zinc-blende AlN

AlN is a wide bandgap semiconductor with numerous potential applications including high temperature, high power devices operating in aggressive media as well as biomedical devices and sensors. At ambient conditions AlN crystallizes in the hexagonal wurtzite structure. A portion of this presentation is devoted to studying the influence of deposition temperature on the quality of wurtzite AlN films deposited by plasma source molecular beam epitaxy (PSMBE) on 6H-SiC substrates. Atomic force microscopy (AFM) and reflection high energy electron diffraction (RHEED) indicate that a change from pseudomorphic to three-dimensional growth mode occurs above 640°C. Films deposited at as low as 500°C showed low leakage current, comparable to the lowest value reported so far.; The metastable cubic zinc-blende structure of AlN is expected to be easier to dope and thus, to be more desirable for device applications than wurtzite AlN. Very little is known about the mechanical, optical and electrical properties of zinc-blende AlN since films with sufficient quality and thickness for such measurements were not available.; We were the first group to grow zinc-blende AlN films of thickness up to 100 nm with high enough quality to allow future characterization of this material. The films were deposited on Si (001) substrates via PSMBE. Data from RHEED, AFM, x-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) established that the AlN films were zinc-blende. No traces of wurtzite AlN were detected in the films. The zinc-blende AlN/Si interface was further studied via Auger electron spectroscopy (AES) and HRTEM, which revealed the presence of a thin layer of the cubic phase of SiC (3C-SiC). The major factors for the growth of the zinc-blende AlN were determined to be: (i) the unique deposition conditions and (ii) the formation of 3C-SiC layer on the surface of the Si (001) substrate. Zinc-blende AlN was also characterized by spectroscopic ellipsometry and the optical constants and bandgap of the material were determined. This is the first experimental optical data reported for zinc-blende AlN.