Short-range order controlled amphoteric behavior of the Si dopant in Al-rich AlGaN

AlGaN alloys with high Al content offer the possibility to create deep ultraviolet light sources emitting at wavelengths ≤ 240 nm with enhanced quantum efficiency. However, increasing the band gap when the Al content surpasses  ~80% leads to problems with n -type doping of AlGaN alloys with the standard choice of Si donors, due to the formation of the so-called negative Si DX center. In this paper, we show that the amphoteric nature of the Si dopant in AlGaN alloys is fundamentally controlled by the local environment and the ordering of the Ga and Al atoms in the vicinity of the Si atom. Our conclusions are based on advanced characterization sensitive to the local environment of defects and impurities, complemented by electronic structure calculations. We propose that spatial ordering of Ga and Si atoms could allow efficient n -type doping at even higher Al contents, including AlN.