Effects of silicon doping and threading dislocation density on stress evolution in AlGaN films

In-situ wafer curvature measurements were used to study the effect of Si doping on intrinsic growth stress during the metalorganic chemical vapor deposition (MOCVD) growth of Al _xGa _1-xN (X=0-0.62) layers on SiC substrates. Post-growth transmission electron microscopy (TEM) characterization was used to correlate measured changes in stress with changes in film microstructure. Si doping was found to result in the inclination of edge-type threading dislocations (TDs) in Al _xGa _1-xN which resulted in a relaxation of compressive stress and generation of tensile stress. The experimentally measured stress gradient was similar to that predicted by an effective climb model. Dislocation inclination resulted in a reduction in the TD density for Si-doped layers compared to undoped Al _xGa _1-xN likely due to increased opportunities for dislocation interaction and annihilation. The TD density, which increased with increasing Al-fraction, was found to significantly alter the stress gradients in the films. Film stress was also observed to play a role in TD inclination. In undoped Al _xGa _1-xN, TD inclination was observed only when the film grew under a compressive stress while in Si-doped Al _xGa _1-xN, TD inclination was observed independent of the sign or magnitude of the film stress. Si dopants are believed to alter the concentration of surface vacancies which gives rise to dislocation jog via a surface-mediated climb mechanism.