title: Surface Plasmon Polariton Cross-Coupling Enhanced Forward Emission from Insulator-Metal-Capped ZnO Films.
abstract: Increasing light extraction efficiency in the forward direction is being extensively pursued due to its crucial role in realizing top-emitting organic and inorganic light emitting devices. Various surface plasmon polariton (SPP)-based strategies for emission enhancement and light extraction have been developed to improve the top-emitting efficiency of these devices. However, the role of surface roughness of both semiconductor film and metal electrode in improving the emission efficiency of a practical device has not been thoroughly studied yet. In this work, the influence of surface roughness of a top metal electrode on the photoluminescence enhancement of a ZnO thin film is investigated experimentally and numerically based on an insulator-metal-semiconductor system. It is found that the generic surface roughness of the metal electrode plays an encouraging role in increasing the forward-emission intensity by facilitating cross-coupling of SPPs on the two opposite sides of the metal layer. More importantly, the forward emission can be further enhanced by capping a high-index polymer layer on the metal electrode to bridge the momentum mismatch between the two SPPs modes. The experimental observations are well explained by the SPPs cross-coupling mechanism that models the radiation power of a dipolar emitter underneath the metal electrode as a function of the metal surface roughness. Our work opens up the possibility of using cross-coupling of SPPs as an effective means to fabricate high-brightness top-emitting devices without the need of complicated nanoscale patterning.
authors.affiliation: Department of Applied Physics, The Hong Kong Polytechnic University , Hong Kong, China.
authors.forename: Dang Yuan
authors.initials: DY
authors.lastname: Lei
authors.affiliation: Department of Electrical and Computer Engineering, National University of Singapore , 4 Engineering Drive 3, Singapore 117583.
authors.forename: Lei
authors.initials: L
authors.lastname: Zhang
authors.affiliation: Department of Physics, The Chinese University of Hong Kong , Hong Kong, China.
authors.forename: Hock Chun
authors.initials: HC
authors.lastname: Ong
keywords: ZnO film; cross-coupling; momentum matching; photoluminescence; roughness; surface plasmon polariton