The MOVPE growth mechanism of catalyst-free self-organized GaN columns in H2 and N2 carrier gases

•Using nitrogen as the carrier gas, Ga droplets accumulation is observed on the top of GaN columns.•The Ga droplets are transformed into high quality GaN due to nitridation during the cool down phase.•Hydrogen carrier gas improves the crystalline quality of overall GaN columns substantially and increases the vertical growth rate. In this case, no indication of Ga droplets could be detected.•Adding silane to the growth atmosphere increases the vertical growth rate substantially.

Columnar structures of III–V semiconductors recently attract considerable attention because of their potential applications in novel optoelectronic and electronic devices. In the present study, the mechanisms for the growth of catalyst-free self-organized GaN columns on sapphire substrate by metal organic vapor phase epitaxy have been thoroughly investigated. The growth behaviours are strongly affected by the choice of carrier gas. If pure nitrogen is used, Ga droplets are able to accumulate on the top of columns during growth, and they are converted into a high quality GaN layer during the cool down phase due to nitridation. Hydrogen as the carrier gas can improve the optical quality of the overall GaN columns substantially, and in addition increase the vertical growth rate. In this case, no indication of Ga droplets could be detected. Furthermore, silane doping during the growth promotes the vertical growth in both cases either pure nitrogen or pure hydrogen as the carrier gas.