Characteristics of a-plane GaN films grown on optimized silicon-dioxide-patterned r-plane sapphire substrates.

We report on the characteristics of a-plane GaN films directly grown on optimized silicon-dioxide-patterned r-plane sapphire substrates. Various shapes and sizes of silicon dioxide patterns were considered with the aim of achieving fully coalescent a-plane GaN films with a smooth surface and high crystalline quality. The omega full widths at half maximum of the (11–20) X-ray rocking curve values of optimized a-plane GaN films with regular hexagonal patterns of 1μm window width and 6μm mask width were measured to be 597arc sec along the c-axis direction and 457arc sec along the m-axis direction. Atomic force microscopy images revealed a significant reduction in the density of submicron pits in the mask region. Plan-view and cross-sectional transmission electron microscopy images showed that basal stacking faults and threading dislocation densities were reduced from ~5.7×105 cm−1 and ~1×109 cm−2 in the window region to ~1.8×105 cm−1 and ~2.1×108 cm−2 in the mask region, respectively. [ABSTRACT FROM AUTHOR]