Magnesium induced changes in the selective growth of GaN by metalorganic vapor phase epitaxy

Atmospheric pressure metalorganic vapor phase epitaxy is used to perform selective regrowth of GaN on a silicon nitride patterned mask, capping a GaN epitaxial layer deposited on (0001) sapphire substrate. The basic pattern is constituted by a 15 mu m period hexagonal array of hexagonal openings in the mask, these openings being circumscribed into 10 mu m diam circles. We investigate the effect of Mg incorporation on the growth anisotropy of the localized GaN islands by varying the ratio [Mg]/[Ga] of bis-methylcyclopentadienyl-magnesium and trimethylgallium partial pressures. Both undoped and Mg-doped GaN hexagonal pyramids, delimited by C (0001) and R (<1(1)over bar 01>) facets, are achieved with a good selectivity. It is found that the GaN growth rates V-R and V-C, measured in the R[<1(1)over bar 01>] and C [0001] directions respectively, are drastically affected by the Mg incorporation. By adjusting the Mg partial pressure in the growth chamber, the V-R/V-C ratio can be increased so that the delimiting top C facet does not vanish as usually observed in undoped GaN localized growth, but by contrast expands. (C) 1998 American Institute of Physics.