Surface morphology of GaN: Flat versus vicinal surfaces

The surface morphology of GaN films grown by molecular beam epitaxy (MBE) i s investigated by scanning tunneling microscopy (STM). A comparison is made between flat and vicinal surfaces. The wurtzite structure of GaN leads to special morphological features such as step pairing and triangularly shaped islands. Spiral mounds due to growth at screw threading dislocations are d ominant on flat surfaces, whereas for vicinal GaN, the surfaces show no spi ral mound but evenly spaced steps. This observation suggests an effective s uppression of screw threading dislocations in the vicinal films. This findi ng is confirmed by transmission electron microscopy (TEM) studies. Continue d growth of the vicinal surface leads to step bunching that is attributed t o the effect of electromigration.