Abstract
High quality nanometer-thick Gd 2 O 3 and Y 2 O 3 (rare-earth oxide, R 2 O 3 ) films have been epitaxially grown on GaN (0001) substrate by molecular beam epitaxy (MBE). The R 2 O 3 epi-layers exhibit remarkable thermal stability at 1100 °C, uniformity, and highly structural perfection. Structural investigation was carried out by in situ reflection high energy electron diffraction (RHEED) and ex-situ X-ray diffraction (XRD) with synchrotron radiation. In the initial stage of epitaxial growth, the R 2 O 3 layers have a hexagonal phase with the epitaxial relationship of R 2 O 3 (0001) H 〈112̄0〉 H //GaN(0001) H 〈112̄0〉 H. With the increase in R 2 O 3 film thickness, the structure of the R 2 O 3 films changes from single domain hexagonal phase to monoclinic phase with six different rotational domains, following the R 2 O 3 (2̄01) M [020] M //GaN(0001) H 〈112̄0〉 H orientational relationship. The structural details and fingerprints of hexagonal and monoclinic phase Gd 2 O 3 films have also been examined by using electron energy loss spectroscopy (EELS). Approximate 3-4 nm is the critical thickness for the structural phase transition depending on the composing rare earth element. © 2013 American Chemical Society.