Bandgap narrowing and Mott transition in Si-doped Al_(0.7)Ca_(0.3)N

摘要

Deep ultraviolet light-emitting diodes (LEDs) composed of III-Nitride semiconductors need layers of heavy doping (1 x 10(19) cm(-3)) to overcome large dopant activation energies and maintain high electrical conductivity. This work reports that at doping densities of [Si] similar to 1.5 x 10(19)/cm(3) for n-Al0.7Ga0.3N, Burstein-Moss and bandgap renormalization effects result in a net reduction of the bandgap of similar to 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 R-sh,R-n = 0.045 Omega cm and rho(c,n) = 1.13 x 10(-6) Omega cm(2) 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. Published under license by AIP Publishing.