Low Operation Voltage of Nitride-Based LEDs with Al-Doped ZnO Transparent Contact Layer

We have developed nitride-based multiquantum well light-emitting diodes (LEDs) with E-beam evaporated Al-doped ZnO (AZO) transparent contact layers (TCLs). With 20 mA injection current, it was found that forward voltages were 3.32, 3.33, and 4.91 V, while output powers were 10.1, 11.8, and 6.0 mW for the indium-tin-oxide LED, E-beam evaporated AZO LED, and sputter-evaporated AZO LED, respectively. The low operation voltage of the E-beam evaporated AZO LED is attributed to the deposition of low-resistivity TCLs, and the elimination of plasma damage in the p-GaN layer is attributed to use of the E-beam evaporated AZO. The high output power of the E-beam evaporated AZO LED is due to the enhancement of light extraction resulting from the high refractive index of AZO TCL. (C) 2008 The Electrochemical Society.