Effect of indium surfactant on stress relaxation by V-defect formation in GaN epilayers grown by metalorganic chemical vapor deposition

Abstract

The effect of indium surfactant on the stress in GaN films grown on SiC at 950 °C by metalorganic chemical vapor deposition was investigated using a combination of in situ wafer curvature measurements and ex situ high resolution x-ray diffraction (HRXRD). As the molar flow rate of trimethylindium was varied from 0 to 4.5 μmol/min during growth, the real-time stress measurements showed that the mean compressive stress of the GaN films decreased from −0.60 to −0.30 GPa. The lattice constants of the GaN epilayers determined by HRXRD confirmed the stress relaxation promoted by the presence of indium while the rocking curve measurements showed that the threading dislocation (TD) density of GaN films remains nearly unchanged. Atomic force microscopy measurements showed that the indium improved step-flow growth, but simultaneously it drove V-defect formation on the GaN surface, which plays a critical role in stress relaxation of GaN films. Cross-sectional transmission electron microscopy revealed the minor contribution of plastic dislocation motion to stress relaxation by localized TD bending toward V-defects. A nucleation and growth model for the V-defect formation was developed to explain that V-defects are energetically favorable to form at TDs under indium-rich conditions. This model shows that the energy barrier for V-defect formation is significantly reduced when indium is present, which leads to the relaxation of misfit strain energy by increasing the size and density of V-defects. Initiation of V-defects and the role of TDs in V-defect formation are discussed based on the presented model.