Effect of Si doping on strain, cracking, and microstructure in GaN thin films grown by metalorganic chemical vapor deposition

The effect of Si doping on the strain and microstructure in GaN films grown on sapphire by metalorganic chemical vapor deposition was investigated. St rain was measured quantitatively by x-ray diffraction, Raman spectroscopy, and wafer curvature techniques. It was found that for a Si concentration of 2x10(19) cm(-3), the threshold for crack formation during film growth was 2.0 mu m. Transmission electron microscopy and micro-Raman observations sho wed that cracking proceeds without plastic deformation (i.e., dislocation m otion), and occurs catastrophically along the low energy {1 (1) under bar 0 0} cleavage plane of GaN. First-principles calculations were used to show t hat the substitution of Si for Ga in the lattice causes only negligible cha nges in the lattice constant. The cracking is attributed to tensile stress in the film present at the growth temperature. The increase in tensile stre ss caused by Si doping is discussed in terms of a crystallite coalescence m odel. (C) 2000 American Institute of Physics. [S0021-8979(00)03410-1].