Effect of hydrogen on morphological changes in columnar structure of GaN grown by ECR–MBE

We investigate the effect of hydrogen on morphological changes in GaN columns grown by electron cyclotron-resonance plasma-excited molecular beam epitaxy on sapphire (0 0 0 1) substrates. In GaN growth with a hydrogen flow of 6 seem, hexagonal columnar structure was obtained. Morphological changes of the GaN columns from hexagonal to triangle were observed by increasing the hydrogen flow rate. It is considered to be caused by preferential growth along three of the six (1 0 0) directions. The surface of the triangle columns consisted of {1 0 1 3} and {1 0 1 1} faceted planes. Formation mechanism of the triangle columnar structure is discussed.