Effects of indium as a surfactant for the growth of Si-doped Al0.75 Ga0.25 N epilayers by metal organic chemical vapor deposition have been studied. It was found that the use of indium as a surfactant improved the overall material quality of these epilayers, as evidenced by decreasing the (a) density of surface pits, (b) screw dislocation density, and (c) intensity of the deep level impurity transition with increasing indium flow rate. Hall effect measurements also yielded increased conductivity and electron concentration with increasing indium flow rate. The results suggested that indium as a surfactant counteracts the incorporation of defects responsible for self-compensation for n -type doping, namely, cation vacancies, in high Al-content AlGaN epilayers. A correlation between the intensity of the deep level impurity transition and screw dislocation density was also established.