Tensile stress generation and dislocation reduction in Si-doped Al_xGa_1-xN films

The effects of Si doping on the evolution of stress in Al_xGa_1-xN:Si thin films (x≈0.4–0.6) grown on 6H-SiC by metal organic chemical vapor deposition were investigated using in situ wafer curvature measurements. The results were correlated with changes in film microstructure as observed by transmission electron microscopy. The incorporation of Si into the films resulted in a compressive-to-tensile transition in the biaxial stress at the surface, and the magnitude of the tensile stress was found to increase in proportion to the Si concentration. The stress gradient was attributed to Si-induced dislocation inclination resulting from an effective climb mechanism. Si doping also resulted in a decrease in the threading dislocation density in the Al_xGa_1-xN layers, which was attributed to increased dislocation interaction and annihilation. The model describing tensile stress generated by dislocation effective climb was modified to account for the dislocation reduction and was found to yield an improved fit to the experimental stress-thickness data.