GaN/AlGaN superlattices for p contacts in LEDs

In order to reduce the access resistance in ultraviolet light-emitting diodes (LEDs), it has been proposed to replace bulk material by the equivalent superlattice. We investigate this idea from the theoretical point of view. We discuss the low field transport in the growth direction of GaN/AlGaN superlattices, in particular with a p doping. We extend the Kronig-Penney model in order to treat the varying potential due to the piezoelectric field which exists in polar materials. We use it to calculate the miniband dispersion in GaN/AlGaN superlattices and clarify the transition from the true superlattice to the multi-quantum well structure. We investigate the variation of vertical conductivity with the period, when the material changes from the equivalent alloy to the superlattice and then to the multi-quantum well structure. Results are used to discuss the interest of using these superlattices in LEDs.