PREPARATION OF WURTZITIC ALN THIN-FILMS WITH A NOVEL CRYSTALLOGRAPHICALIGNMENT ON MGO SUBSTRATES BY MOLECULAR-BEAM EPITAXY

Thin films of wurtzitic AW have been deposited by molecular-beam epita xy onto (001) oriented MgO substrates, The films are epitactic and ali gn with the (2 (1) over bar (1) over bar 0)(AlN) \\ (220)(MgO) and the [01 (1) over bar 1](AlN) \\ [001](MgO), as evidenced by transmission electron microscopy, This configuration, which matches a close-packed direction of the film and substrate, allows for growth of two symmetri cally equivalent orientation variants of the AlN film, These variants are distinguished by a 90 degrees rotation about the [01 (1) over bar 1](AlN) direction that is normal to the substrate surface. Each varian t also aligns the (0 (1) over bar 12)(AlN) \\ (2 (2) over bar 0)(MgO) and the (1 (1) over bar 01)(AlN) to within 5 degrees of being parallel to the (200)(MgO). The microstructure of the AlN films and origins of these novel alignments are discussed.