Effect of an In layer on the thermal stability of Ag reflector for vertical GaN-based light-emitting diodes

We investigated the effect of an indium (In) middle layer on the thermal and electrical properties of Ag contacts for high-power GaN-based vertical light-emitting diodes (LEDs). It is shown that with increasing temperature, agglomeration is initiated by the formation of hillocks, followed by the generation of holes, eventually leading to agglomeration. The presence of the In layer effectively delays agglomeration. As a result, the In-combined Ag reflectors exhibit better specific contact resistance (6.0 × 10−5 Ω cm2) and reflectance (∼75% at 440 nm) when annealed at 500 °C, as compared to Ag only contacts. Blue (440 nm) LEDs fabricated with the 500 °C-annealed In-combined Ag contacts exhibit a forward voltage of 2.99 V (at an injection current of 20 mA) lower than that of LEDs with the 500 °C-annealed Ag only contacts. The output power (at 20 mA) of the LEDs with the 500 °C-annealed In-combined Ag contacts is 29% higher than that of LEDs with the 500 °C-annealed Ag only contacts.

► An In layer employed to enhance the thermal stability of Ag ohmic reflectors.
► The use of an In layer efficiently delays the agglomeration of Ag reflector.
► In-combined contacts exhibit better electrical behavior than Ag only contacts.
► LEDs with In-combined contact show higher performance than LEDs with Ag only contact.