Effect of mask material on selective growth of GaN by RF-MBE

The selective growth mechanism of GaN on a (0 0 0 1) GaN template using radio-frequency plasma-assisted molecular beam epitaxy is investigated. The effect of the mask material on selective growth is investigated using SiO2 and Ti masks. Selective growth of GaN with excellent selectivity and a smooth surface is achieved by optimizing the growth temperature. The threshold temperatures for selective growth are 930 and 940 °C for SiO2 and Ti masks, respectively. A high growth temperature is necessary to suppress the formation of polycrystals on the mask and to obtain selective growth. The different threshold temperatures are thought to be due to the different affinities between Ga adatoms and the two mask materials. Selective growth is also performed using wide masks. Re-evaporation of adatoms is found to be the principal process in the selective growth obtained using the SiO2 mask, whereas adatom migration is the principal process with the Ti mask. Surface diffusion of adatoms on the Ti mask results in the formation of a denuded zone near the mask edge and protuberances on both sides of the selective growth.

► Selective growth of GaN was performed by MOMBE.
► Effect of Ti mask and SiO2 mask on the selective growth was investigated.
► Re-evaporation of adatoms is the principal process for SiO2 mask.
► Adatom migration is the principal process for Ti mask.
► Cross-sectional shape is determined by the adatom diffusion.