Polarity and Its Influence on Growth Mechanism during MOVPE Growth of GaN Sub-micrometer Rods

The influence of polarity during the MOVPE growth of GaN based sub-micrometer (sub-mu m) rods has mostly been neglected up to now. In this paper we demonstrate that the surface polarity plays a crucial role for the morphology of the GaN sub-mu m rods. Based on the differences between N-polar and Ga-polar surfaces, a model is suggested to explain the influence of various parameters on the morphology of GaN sub-mu m rods for the first time. For Ga-polar GaN,, the {10-11} r-planes, similar to N-polar (000-1) c-planes, are terminated by nitrogen atoms. These N-terminated surfaces can be passivated by hydrogen, which leads to a stable surface with low growth rates and therefore tends to keep a pyramidal shape with stable r-planes. For N-polar GaN, {10-1-1} r-planes can be modified by H(2) etching, leading to the formation of more stable {1-100} m-planes, hence supporting the formation of sub-mu m rods with vertical sidewalls.