Defects and defect reactions in semiconductor nitrides

We report a comprehensive investigation of native point-defects and impurit ies in GaN, AlN, and AlGaN alloys, with the goal of understanding doping li mitations in nitride semiconductors. Unintentional incorporation of impurit ies (mainly oxygen) explains the tendency of nitride semiconductors to exhi bit n-type conductivity. Silicon is the n-type dopant of choice; it remains shallow in AlGaN up to high Al content, while oxygen undergoes a DX transi tion. Experimental evidence for DX centers mill be discussed. In p-type mat erial, Mg doping is hindered by an increase in ionization energy with incre asing Al content in AlGaN, and by nitrogen vacancies acting as compensating centers. Complex formation between magnesium and oxygen and between magnes ium and nitrogen vacancies will be discussed.