NOVEL SYMMETRY IN THE GROWTH OF GALLIUM NITRIDE ON MAGNESIUM ALUMINATE SUBSTRATES

The growth of GaN by metalorganic chemical vapor deposition on (111) a nd (100) magnesium aluminate (MgAl2O4) substrates is examined using tr ansmission electron microscopy. The results indicate that mainly wurtz ite GaN is grown for both orientations. On the (111) substrate the fol lowing epitaxial relationship is observed: (0001)GaN parallel to (111) MgAl2O4, and [11 (2) over bar 0]GaN parallel to [1 (1) over bar 0]MgAl 2O4. During the early stages of the (100) growth, four orientations of the wurtzite phase and a zinc-blende phase are formed. With increasin g thickness, one of the wurtzite orientations dominates, with the epit axial relationship being (1 (1) over bar 01)GaN parallel to (100)MgAl2 O4 and the [11 (2) over bar 0]GaN nearly parallel to [011]MgAl2O4. Thi s choice of growth orientation appears to be determined primarily by t he nature of the interfacial bonding, with the basal plane of each of the four wurtzite GaN variants being nearly aligned along one of the f our (111) planes intersecting the (100) surface of the MgAl2O4. (C) 19 96 American Institute of Physics.