| Abstract: | Ultraviolet light-emitting diodes with tailored AlGaN quantum wells can
achieve high extraction efficiency. For efficient bottom light
extraction, parallel polarized light is preferred, because it propagates
predominately perpendicular to the QW plane and into the typical and more
efficient light escape cones. This is favored over perpendicular
polarized light that propagates along the QW plane which requires
multiple, lossy bounces before extraction. The thickness and carrier
density of AlGaN QW layers have a strong influence on the valence subband
structure, and the resulting optical polarization and light extraction of
ultraviolet light-emitting diodes. At Al>0.3, thinner QW layers
(<2.5 nm are preferred) result in light preferentially polarized
parallel to the QW plane. Also, active regions consisting of six or more
QWs, to reduce carrier density, and with thin barriers, to efficiently
inject carriers in all the QWs, are preferred. |