Dislocation bending and tensile stress generation in GaN and AlGaN films

The growth of GaN and AlGaN films is accompanied by dislocation bending, interaction, density reduction and tensile stress generation to varying degrees. A kinetic model involving outdiffusion of atoms at the growth surface has been adapted to rationalize all of these phenomena using a single platform. Active contribution of dislocation interaction, apart from stress and a surface chemical potential, to the driving force for outdiffusion of atoms from the growth surface has been considered. The kinetic model has then been used to explain stress evolution during growth of GaN films on Si using an AlN buffer layer, an example of a most general case. Stress–thickness relations obtained from the model have been fitted to experimental data to derive basic outdiffusion parameters. These parameters have been used to analyze experimental observations of dislocation structure evolution. The model is able to account for the varying degrees of dislocation bending and interaction observed in these films.

► A kinetic, as opposed to thermodynamic, approach to dislocation structure evolution during group-III nitride growth. ► Model includes effect of dislocation interaction and bending and is therefore a general one. ► Model predicts angles through which dislocations bend as observed by TEM images well. ► Model has only one fitting parameter whose physical origins are discussed. ► Model also accounts for misfit dislocation segment formations close to the interface other than those formed by bending.