Use of graphene for forming Al-based p-type reflectors for near ultraviolet InGaN/AlGaN-based light-emitting diode

• Highly reflective Al-based p-type reflectors for UV-LEDs were investigated.
• Graphene sheets are used as a barrier to the indiffusion of Al atoms toward p-GaN.
• ITO/graphene/Al contact show lower contact resistance than that of reference contact.
• LEDs with ITO/graphene/Al contact show a higher light output than reference LEDs.

We demonstrated the improved performance of near UV (365 nm) InGaN/AlGaN-based LEDs using highly reflective Al-based p-type reflectors with graphene sheets as a diffusion barrier. The use of graphene sheets did not degrade the reflectance of ITO/Al contacts, viz. ∼81% at 365 nm. The ITO/graphene/Al contacts annealed at 300 °C exhibited better ohmic behavior with a specific contact resistance of 1.5 × 10−3 Ωcm2 than the ITO/Al contact (with 9.5 × 10−3 Ωcm2). Near UV LEDs fabricated with the ITO/graphene/Al contact annealed at 300 °C showed a 7.2% higher light output (at 0.1 W) than LEDs with the ITO/Al reflector annealed at 300 °C. The SIMS results exhibited that, unlike the ITO/graphene/Al, the ITO/Al contacts undergo a significant indiffusion of Al atoms toward the GaN after annealing. Furthermore, both Ga and Mg atoms were also more extensively outdiffused in the ITO/Al contacts after annealing. On the basis of the SIMS and electrical results, the possible explanations for the annealing-induced degradation of the ITO/Al contacts are described and discussed.