Surface instability and associated roughness during conventional and pendeo-epitaxial growth of GaN(0001) films via MOVPE
Investigations of the origins of surface roughening in GaN(0001) have resulted in the development of a growth process route having an optimum temperature of 1020degreesC and a film thickness beyond 2.5 mum which results in films with the smoothest surface morphology. Atomic force microscopy (AFM) revealed uncoalesced GaN islands and hillocks for non-optimum temperatures below and above 1020degreesC, respectively. Uncoalesced islands were a result of insufficient lateral growth. Hillocks were a result of the rotation of heterogeneous steps formed at pure screw or mixed dislocations which terminated on the (0001) surface. Growth of the latter features was controlled kinetically by temperature through adatom diffusion. The 10(6) cm(-2) density of hillocks was reduced through growth on thick GaN templates and regions of pendeo-epitaxy (PE) overgrowth with lower pure screw or mixed dislocations. Smooth PE surfaces were obtained at temperatures that reduced the lateral to vertical growth rate but also retarded hillock growth that originated in the stripe regions. The (11 (2) over bar0 ) PE sidewall surface was atomically smooth, with a root mean square roughness value of 0.17 nm, which was the noise limited resolution of the AFM measurements. (C) 2002 Published by Elsevier Science B.V.