Relaxation mechanisms in metal-organic vapor phase epitaxy grown Al-rich (Al,Ga)N/GaN heterostructures -: art. no. 024912

The relaxation mechanisms in metal-organic vapor phase epitaxy grown (Al,Ga)N/GaN heterostructures are studied. The first stage of the relaxation process is a two-dimensional-three-dimensional growth transition with the formation of mesalike islands separated by V-shaped trenches. The tensile stress relief is obtained by an elastic relaxation of the islands edges. In the case of AlN/GaN, the apexes of the V trenches reach the heterointerface and misfit dislocations are nucleated at the islands coalescence region. These dislocations are a type and glide in the basal plane to promote further relaxation. For (Al,Ga)N/GaN with an Al concentration below 70%, the apexes of the V trenches do not reach the heterointerface, prohibiting the nucleation of misfit dislocations. For thicker layers, the next stage of the relaxation is the cracking of the films. (C) 2005 American Institute of Physics.