Enhancement of the External Quantum Efficiency of a Silicon Quantum Dot Light‐Emitting Diode by Localized Surface Plasmons

Abstract

Effective light emission from low-dimensional silicon materials such as porous silicon, silicon nanocrystals, and superlattices has been demonstrated at room temperature in spite of the indirect bandgap nature of bulk silicon. [1][2][3][4][5] In particular, silicon quantum dot (Si QD) light-emitting diodes (LEDs) have recently been investigated as a promising light source for the next generation of optical interconnections. [6][7][8] However, the quest for highly efficient Si QD LEDs remains unfulfilled. To achieve this goal, new LED structures are being developed to enhance the external quantum efficiency (h ext ), which is a product of the light-extraction efficiency (h extraction ), radiative efficiency (h rad ), and current-injection efficiency (h inj ). [9] Among the new approaches, increasing the radiative recombination rate by coupling QDs to surface plasmons (SPs, collective charge oscillations at the interface between a metal and a dielectric material) has attracted a great deal of attention. [10][11][12] Although enhanced photoluminescence (PL)of SP-coupled nanostructures such as QDs [13][14][15][16][17] and quantum wells (QWs) [18] has been reported, there has been no report concerning the enhancement of electroluminescence (EL) in Si QD LEDs through a Si QD-SP coupling effect. Here, we show the first evidence of enhanced h ext in a Si QD LED resulting from the coupling between Si QDs and localized surface plasmons (LSPs) and effective current tunneling into Si QDs from an Ag layer containing Ag particles inserted between the Si QD layer and Si substrate. Surface plasmon excitations in bounded geometries, such as nanostructured metallic particles, are LSPs. The resonant excitation of LSPs on the surface of nanostructured metallic particles by an incident electromagnetic field (light) causes strong light scattering and absorption, and enhanced local electromagnetic fields. LSPs are generally used in many applications such as ultrafast switches, optical tweezers, labeling biomolecules, optical filters, biosensors, surface-enhanced spectroscopies, plasmonics, and chemical sensors. [19][20][21][22] SPs are evanescent waves that exponentially decay with distance from a metal surface. Si QDs located within the near-field of the metal surface can be effectively coupled to SP mode. [13,18,19] In order to keep the close distance between SiQDs and the metal layer for Si QD-LSP coupling, we propose a Si QD LED structure with an Ag layer containing Ag particles inserted between the silicon nitride layer containing Si QDs and the Si substrate layer, as shown in Figure 1. Figure 2a and b shows cross-sectional transmission electron microscopy (TEM) images of Si QD LEDs with and without an Ag layer. Figure 2a depicts the interface between the silicon nitride and Si substrate of a reference Si QD LED. Figure 2b is an image of the interfaces between the silicon nitride layer, Ag layer, and the Si substrate. The silicon nitride film deposited on the Ag layer was similar in thickness to the silicon nitride layer in the re...

Surface plasmon enhanced blue–green photoluminescence from carbon-rich amorphous silicon carbide films

“…For example, Yeh et al [13] have recently enhanced the InGaN/GaN LED emission intensity by 150% relative to a LED without an Ag layer. Kim et al [3] reported a 4.3-fold EL enhancement of Si-QDs LED by QD-Ag coupling. In Cheng et al's [16] report on the ZnO films, a maximum photoluminescence (PL) enhancement factor of 3 was achieved via SPs.…”

“…SPs are the collective oscillations of free electrons in a metal, which occur at the interfaces between metals and dielectrics [2]. In addition to the propagating surface plasmons (PSPs) on a plane surface, the collective oscillations of electrons in metal nanoparticles embedded in a dielectric matrix are localized surface plasmons (LSPs) [3,4]. Either PSP or LSP can interact with nearby light emitter through its evanescent or near-field coverage for enhancing emission [5].…”

“…Ag was most commonly used in the visible spectral range as it has the lowest loss of SP energy in this region [10,11]. In recent years, PSPs and LSPs of Ag have been extensively studied to enhance the luminescence efficiency of light emitting materials and devices, such as InGaN/GaN [1,4,12,13], silicon quantum dots (Si-QD) [3,14], and ZnO films [15][16][17][18][19], for the applications of ultrabright light-emitting diodes (LEDs), or ultraviolet UV lasers. For example, Yeh et al [13] have recently enhanced the InGaN/GaN LED emission intensity by 150% relative to a LED without an Ag layer.…”

Amorphous carbon-based films with surface-plasmon-enhanced full-color photoluminescence

“…SPs are the collective oscillations of free electrons in a metal, which occur at the interfaces between metals and dielectrics [4]. In addition to the propagating surface plasmons (PSPs) on a plane surface, the collective oscillations of electrons in metal nanoparticles embedded in a dielectric matrix are localized surface plasmons (LSPs) [5,6]. Either PSP or LSP, an SP can interact with the light emitter nearby through its evanescent or near-field coverage for enhancing emission [7].…”

“…The emission efficiency is enhanced via an alternative radiation channel, in which the energy of the light emitter is firstly transferred into the propagating or localized SP modes and then into the radiation modes [8]. In the past two decades, SPs have been extensively studied to enhance the luminescence efficiency of light emitting materials and devices, such as InGaN/GaN [3,6,9,10], silicon quantum dots (Si-QD) [5] and ZnO films [11][12][13][14][15][16], for the applications of ultrabright light-emitting diodes (LEDs), or ultraviolet UV lasers. In our previous studies, SPs were successfully used to enhance the light emission from a-Si 1 − x C x :H films (emitting blue-green light at 480 nm) [17] and a-C:H films (emitting blue light at 445 nm) [18].…”