Effects on electrical and optical properties of InGaN/GaN MQWs light-emitting diodes using Ni/ITO transparent p-contacts on p-GaN

In the present study, optical and electrical properties of e-beam-deposited Ni/indium–tin oxide (5/50 nm) contacts are studied and compared with semi-transparent Ni/Au (5/5 nm) contacts. The normalized transmittance of 560 °C annealed Ni/ITO and Ni/Au films was recorded 86% and 73.1% at 463 nm, respectively. The current–voltage characteristics of both annealed contacts exhibit the linear behavior. The specific contact resistances for Ni/Au and Ni/ITO contacts were recorded 1.29 × 10⁻³ Ω cm² and 1.76 × 10⁻¹ Ω cm², respectively. The forward voltages (V_F) of LEDs for both contacts (Ni/Au and Ni/ITO p-contacts) at 20 mA current injection were found 2.8 V and 3.11 V, respectively. It is clear that electrical properties of LEDs with Ni/Au contacts are found much better compared to LEDs with Ni/ITO p-contacts. On the other hand, optical characteristics of LEDs with Ni/ITO contacts showed better optical properties compared to LEDs with Ni/Au contacts. The better optical properties were attributed to more transparent nature of ITO film in the visible range. With a 20 mA current injection, the electroluminescence (EL) intensity of blue LED with Ni/ITO p-contact was 14.9% higher than LED with Ni/Au contacts.