Strain-driven light-polarization switching in deep ultraviolet nitride emitters

Abstract

Residual strain plays a critical role in determining the crystalline quality of nitride epitaxial layers and in modifying their band structure; this often leads to several interesting physical phenomena. It is found, for example, that compressive strain in Al${}_{x}$Ga${}_{1\ensuremath{-}x}$N layers grown on Al${}_{y}$Ga${}_{1\ensuremath{-}y}$N ($x$ $y$) templates results in an anticrossing of the valence bands at considerably much higher Al composition than expected. This happens even in the presence of large and negative crystal field splitting energy in the Al${}_{x}$Ga${}_{1\ensuremath{-}x}$N layers. A judicious magnitude of the compressive strain can support vertical light emission (out of the c-plane) from Al${}_{x}$Ga${}_{1\ensuremath{-}x}$N quantum wells up to $x$ \ensuremath{\approx} 0.80, which is desirable for the development of deep ultraviolet light-emitting diodes designed to operate at or below 250 nm with transverse electric polarization characteristics.