Electrical and optical properties of InGaN/GaN MQWs light-emitting diodes with Ni/Au/ITO transparent p-contacts

Abstract

In the present study, optical and electrical properties of e-beam deposited Ni/Au/ITO (1.5/1/50 nm) contacts on p-GaN are investigated and compared with conventional thin Ni/Au (5/5 nm) semitransparent p-contacts. The contacts were annealed at 560 °C for 5 min in N₂ + O₂ ambient in a rapid thermal annealing system. The current–voltage (I–V) characteristics of both metal schemes showed linear behavior. The specific contact resistances and sheet resistances extracted from measured resistance versus contact pads spacing of Ni/Au and Ni/Au/ITO contacts were recorded ~ 2.71 × 10⁻³ Ω-cm², 4.94 × 10⁻⁴ Ω-cm², 2.021 × 10⁵ Ω/□ and 2.1898 × 10⁵ Ω/□, respectively. The normalized transmittance of Ni/Au/ITO film was recorded 81.6% at 463 nm, which was 8.5% higher than the conventional Ni/Au film (73.1%). Scanning electron microscopy images of contacts showed that the adhesion quality of Ni/Au/ITO contacts was superior to annealed Ni/Au contacts. It was found that electroluminescence intensity was higher (7.5%) for LED chip with Ni/Au/ITO p-contacts than LED chip with Ni/Au contacts. The forward voltages (V_F) of LEDs with Ni/Au and Ni/Au/ITO contacts at 20 mA current injection were found 2.8 V and 2.91 V, respectively. These results indicate that Ni/Au/ITO may be used as transparent p-contacts for fabrication of high-performance GaN LEDs due to their better optical and adhesive properties compared to the conventional Ni/Au (5/5 nm) contacts on p-GaN.