Impact of Interlayer Processing Conditions on the Performance of GaN Light-Emitting Diode with Specific NiOx/Graphene Electrode

This paper reports on the evaluation of the impact of introducing interlayers and postmetallization annealing on the graphene/p-GaN ohmic contact formation and performance of associated devices. Current–voltage characteristics of the graphene/p-GaN contacts with ultrathin Au, Ni, and NiOx interlayers were studied using transmission line model with circular contact geometry. Direct graphene/p-GaN interface was identified to be highly rectifying and postmetallization annealing improved the contact characteristics as a result of improved adhesion between the graphene and the p-GaN. Ohmic contact formation was realized when interlayer is introduced between the graphene and p-GaN followed by postmetallization annealing. Temperature-dependent I–V measurements revealed that the current transport was modified from thermionic field emission for the direct graphene/p-GaN contact to tunneling for the graphene/metal/p-GaN contacts. The tunneling mechanism results from the interfacial reactions that occur between the ...