Silicon-Related Defects in AlN from First Principles

We employ hybrid functionals in density functional theory to investigate the formation of silicon-related defect complexes with oxygen, hydrogen, and nitrogen vacancies in aluminium nitride (AlN) to elucidate their electronic properties and impact on conductivity. Silicon and oxygen are both known as shallow donors in GaN, but form stable DX centres in AlN, which act as compensating centers in high-Al-content alloys. Our findings suggest that silicon and oxygen can form a stable complex that leads to the deactivation of the Si donor. Silicon complexed with a nitrogen vacancy is characterized by a higher formation energy than other computed defects, and also exhibits (-) and (2-) negative charge states close to the conduction-band minimum. The interplay of defects and complexes will influence the material's electronic performance significantly. Our calculations help disentangle experimental measurements and provide deeper insights into the role of each of the defects and complexes in AlN and high-Al-content alloys.