Abstract
Surface plasmon (SP)-enhanced quantum-well (QW) LEDs have proved their potential in replacing conventional lighting devices for their high-performance capabilities in ultraviolet (UV), blue and green spectral ranges. The SP-enhanced QW-LEDs have applications in light emission enhancement, light polarization, color conversion, and speed modulation. The electric field of the plasmonic mode of a metal couples with the exciton energy of QWs in resonance results in efficiency enhancement to several folds. The strength of the SP–QW coupling is mainly influenced by the type of metal used for SP enhancement, the metal nanostructure geometry, and the penetration depth of the SP fringing field in the p-GaN. The use of an appropriate dielectric interlayer between the metal and the p-GaN allows further control over SP resonance with QW emission wavelength. The penetration depth defines the p-GaN thickness and the QW period number for effective SP–QW coupling. The optimization of these parameters is key to achieve high efficiencies in SP-enhanced QW-LEDs for various applications. This review explains the SP enhancement mechanism and the key challenges facing the SP enhancement of QW-LEDs. The main factors that affect the SP–QW coupling have been explained in detail based on recent reports devoted to this field.
Highlights
The surface charge density oscillations that exist at a metal–dielectric interface are known as surface plasmons
The external quantum efficiency (EQE) of a QW-LED depends on its injection efficiency, internal quantum efficiency (IQE), and light extraction efficiency (LEE)
The results suggest that the dielectric properties of the dielectric interlayer (DI) affect the Surface plasmon (SP)–QW coupling strength
Summary
The surface charge density oscillations that exist at a metal–dielectric interface are known as surface plasmons. SPs at the metal surface can interact with light of the same frequency and wave vector, thereby generating a fluctuating electric field at the interface. The. SPs generate giant electromagnetic fields that can support light emission, absorption, and scattering enhancement in various materials and devices. Light emission enhancement in LEDs is one of the most important applications of plasmonics due to the growing need for energy-efficient devices. To achieve the SP enhancement in QW-LEDs, the plasmonic metal structures are formed on the p-GaN surface layer. For the successful SP–QW coupling, the p-type layer should be kept sufficiently thin The possible workarounds such as metal protrusions, embedded metal NPs, and the deep metal grating structures are effective but costly and complicated [19,20,21,22,23,24]. This review explains the basic SP–QW coupling mechanism, key challenges and the most important factors affecting the SP enhancement in QW-LEDs based on recent reports devoted to this field
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