title: Impact of interlayer processing conditions on the performance of GaN light-emitting diode with specific NiOx/graphene electrode.
abstract: 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 NiO(x) 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 metal and p-GaN during the postmetallization annealing. InGaN/GaN light-emitting diodes with NiO(x)/graphene current spreading electrode offered a forward voltage of 3.16 V comparable to that of its Ni/Au counterpart, but ended up with relatively low light output power. X-ray photoelectron spectroscopy provided evidence for the occurrence of phase transformation in the graphene-encased NiO(x) during the postmetallization annealing. The observed low light output is therefore correlated to the phase change induced transmittance loss in the NiO(x)/graphene electrode. These findings provide new insights into the behavior of different interlayers under processing conditions that will be useful for the future development of opto-electronic devices with graphene-based electrodes.
authors.affiliation: School of Semiconductor and Chemical Engineering, Semiconductor Physics Research Center, Chonbuk National University, Jeonju 561-756, South Korea.
authors.forename: S
authors.initials: S
authors.lastname: Chandramohan
authors.forename: Ji Hye
authors.initials: JH
authors.lastname: Kang
authors.forename: Beo Deul
authors.initials: BD
authors.lastname: Ryu
authors.forename: Jong Han
authors.initials: JH
authors.lastname: Yang
authors.forename: Seongjun
authors.initials: S
authors.lastname: Kim
authors.forename: Hynsoo
authors.initials: H
authors.lastname: Kim
authors.forename: Jong Bae
authors.initials: JB
authors.lastname: Park
authors.forename: Taek Yong
authors.initials: TY
authors.lastname: Kim
authors.forename: Byung Jin
authors.initials: BJ
authors.lastname: Cho
authors.forename: Eun-Kyung
authors.initials: EK
authors.lastname: Suh
authors.forename: Chang-Hee
authors.initials: CH
authors.lastname: Hong