The first direct atomic scale experimental observations of O segregation to screw dislocations in GaN were made here by using correlated techniques in a scanning transmission electron microscope. The amount of O present in each of the 3 distinct types of screw dislocation core was found to depend upon the evolution and structure of the core, and thus gives rise to a varying concentration of localized states in the band gap. Contrary to previous theoretical predictions, the substitution of O for N was observed to extend over many monolayers for the open core dislocation.

Role of Oxygen at Screw Dislocations in GaN. I.Arslan, N.D.Browning: Physical Review Letters, 2003, 91[16], 165501 (3pp)