Bandgap narrowing and Mott transition in Si-doped Al0.7Ga0.3N

Abstract

Deep ultraviolet light-emitting diodes (LEDs) composed of III-Nitride semiconductors need layers of heavy doping (>1 × 1019 cm-3) to overcome large dopant activation energies and maintain high electrical conductivity. This work reports that at doping densities of [Si] ∼1.5 × 1019/cm3 for n-Al0.7Ga0.3N, Burstein-Moss and bandgap renormalization effects result in a net reduction of the bandgap of ∼70 meV. At these doping levels, a transition to a metallic conductivity state is observed, with a vanishing of the effective dopant activation energy. The sheet and contact resistivities of Rsh,n = 0.045 Ω cm and ρc,n = 1.13 × 10-6 Ω cm2 are achieved, with uniform conductivity in the vertical direction. The results show that when heavily doped n-AlGaN cladding regions are used for high efficiency deep-UV LEDs or lasers, the accompanying bandgap narrowing reduces the window of optical transparency at the lowest wavelengths that can take advantage of high conductivity.