Structural characterization of nonpolar (11(2)over-bar0) a-plane GaN thin films grown on (1(1)over-bar02) r-plane sapphire

In this letter we describe the structural characteristics of nonpolar (11 (2) over bar0) a-plane GaN thin films grown on (1 (1) over bar 02) r-plane sapphire substrates via metalorganic chemical vapor deposition. Planar growth surfaces have been achieved and the potential for device-quality layers realized by depositing a low temperature nucleation layer prior to high temperature epitaxial growth. The in-plane orientation of the GaN with respect to the r-plane sapphire substrate was confirmed to be [0001](GaN)parallel to[(1) over bar 101](sapphire) and [(1) over bar 100](GaN)parallel to[11 (2) over bar0](sapphire). This relationship is explicitly defined since the polarity of the a-GaN films was determined using convergent beam electron diffraction. Threading dislocations and stacking faults, observed in plan-view and cross-sectional transmission electron microscope images, dominated the a-GaN microstructure with densities of 2.6x10(10) cm(-2) and 3.8x10(5) cm(-1), respectively. Submicron pits and crystallographic terraces were observed on the optically specular a-GaN surface with atomic force microscopy. (C) 2002 American Institute of Physics.