Optimization of indium tin oxide layer thickness for surface-plasmon-enhanced green light-emitting diodes

Abstract

Surface-plasmon (SP)-enhanced light-emitting diodes (LEDs) covering self-assembled Ag nanoparticles (NPs) on top of a p-GaN layer are broadly studied to improve luminescence efficiency in green LEDs. However, the enhancement factor of SP-enhanced LEDs is reduced under electrical injection compared to that under external optical pumping. For current injection, indium tin oxide (ITO) is typically deposited on top of a p-GaN layer for current spreading and ohmic contact. In this paper, we investigate the effect of the ITO layer on the performance of SP-enhanced green LEDs. We prepared samples with varying ITO thicknesses, from 30 nm to 200 nm, and investigated their optical and electrical characteristics. From the ITO thickness-dependent measurements, we show ITO thickness has a significant impact on electroluminescence intensity and current–voltage characteristics. Finally, we propose the optimized ITO thickness for SP-enhanced LEDs.

Three-Method Hybrid Numerical Simulation for Surface-Plasmon-Enhanced GaInN-Based Light-Emitting Diodes with Metal-Embedded Nanostructures

“…Consequently, the EQE of an LED device with an Ag-NP-embedded nanostructure is expected to be enhanced by as much as ∼1.6 times a conventional LED device in theory (where the IQE and the LEE are 30 and 22% for a conventional LED, respectively). The IQE improvement of ∼30% by SP/LSP mode has been theoretically predicted and experimentally demonstrated in our previous paper [21,22]. Also, the LEE improvement of ∼22% by nanostructure (or photonic crystal) has been experimentally demonstrated in previous papers [8,15].…”

“…2 indicates that the EQE is enhanced by the additional recombination channel (R SPC × C ext ), that is, exciton coupling with the SP/LSP mode enhances the radiative recombination rate. In other words, the IQE is enhanced because an overlap of the local EM-field (see Figures2, 3) increases both the SP coupling rate (R SPC ) and the probability of photon extraction from the SP energy (C ext )[21,33]. Here, the IQE enhanced by the SP/LSP mode can be estimated using the results in Figure3B.…”

“…To improve the IQE, tremendous efforts have been made in epitaxial growth and device fabrication. Of which, surfaceplasmon (SP)-enhanced LEDs have attracted great attention and have been intensively studied because SP-mode works very efficiently in GaInN-based green LEDs [21][22][23][24]. In particular, LEDs with metalnanoparticle (NP)-embedded nanostructures have demonstrated great IQE improvement.…”

Comparative study of III-phosphide- and III-nitride-based light-emitting diodes: understanding the factors limiting efficiency

“…Meanwhile, improving the WPE can be achieved in the red sample by reducing the total internal reflection, e.g. using photonic crystals, surface plasmons, nanopatterned substrates, and surface texturing [42][43][44]. Furthermore, decreasing the junction temperature and optimizing the electrode structure [45] are likely to be effective.…”

Tuning the Resonant Frequency of a Surface Plasmon by Double-Metallic Ag/Au Nanoparticles for High-Efficiency Green Light-Emitting Diodes

“…In practice, it is difficult to realize SP-enhanced LEDs covered with a thin metal film deposited on the device surface because photons typically are emitted into the free space via the device surface. For this reason, SP-enhanced LEDs covered with self-assembled nanoparticles (NPs) on top of a p-GaN layer are often studied [29][30][31][32][33]. In this case, the collective oscillations of electrons in randomly distributed metal NPs coupled with excitons in MQWs occur via localized surface plasmon (LSP) modes.…”