Iridium-based semi-transparent current spreading layer on short-period-superlattice (SPS) tunneling contact of InGaN/GaN LEDs

Iridium-containing and Ni(4 nm)/Au(6 nm) films were evaporated separately on the n⁺-InGaN-GaN short-period-superlattice (SPS) structure of light-emitting diodes (LEDs). The collective deposition of iridium and other metals as an ohmic contact induces the formation of highly transparent IrO₂, which helps to enhance the light output and decrease the series resistance of LEDs. By comparing different metal films used as current spreading contact layer, Ir/Ni film annealed at 500 °C for 20 min in O₂ ambient renders devices with lowest turn-on voltage at 20 mA and highest luminous intensity. Moreover, we also analyzed films using atomic force microscopy (AFM) with an emphasis on studying how the surface quality of Ir/Ni and Ni/Au films influences the current spreading and luminosity of LEDs.