## 3 Results and Discussion  
Figure 2 shows field-emission scanning electron microscopy (FE-SEM) images of Ag NP/NW TCEs with NP sizes and the transmittance of Ag NW and Ag NP/NW TCEs. To form Ag NW TCEs with high conductivity, we used Ag NWs that were 35 nm in diameter and 25 \(\upmu\)m in length [3,16]. The sheet resistance of the 200 nm thick Ag NWs and Ag NW/NP TCEs was measured as 30 \(\pm\) 5 \(\Omega\)/sq. The contact resistance did not change after NPs were added to the TCE. The contact resistance between the TCE with Ag NWs and p-GaN is 2.5 \(\times\) 10\({}^{-3}\)\(\Omega\) cm\({}^{2}\). This is sufficient to form an Ohmic contact on p-GaN [3]. To obtain the leakage mode and scattering centers, we fabricated Ag NPs with sizes of 35 \(\pm\) 13 nm, as shown in Figure 2b,c, respectively. The density of the Ag NPs with a size of 35 \(\pm\) 13 nm was 8 \(\times\) 10\({}^{10}\) cm\({}^{-2}\). We found that the transmittance of the Ag NWs exceeded 90% in the visible region. When the NPs were added, the TCE exhibited strong absorption that corresponds to SP resonance. This result may be caused by the enhancement of localized surface plasmon resonance by Ag NPs [21, 22, 23]. The oxidation of Ag affected the electrical properties of the LED and the SP effect. To confirm that Ag NW and NP was not oxidized, we performed X-ray photoelectron spectroscopy, as shown in Figure 2d. Figure 1d shows that the Ag3d\({}_{5/2}\) peak was 368.3 eV. This indicated Ag NP and NW were not oxidized [24]. Figure 1: Schematic illustrations and images corresponding to steps for the fabrication of GaN LEDs with Ag-NW/NP-based TCE. (**a**) To fabricate LEDs 500 \(\times\) 500 \(\upmu\)m\({}^{2}\) in size, the p-GaN and MQWs were sequentially etched using inductively coupled plasma with boron trichloride gas until n-contact layer was exposed. (**b**) Ag films with thicknesses of 1 nm were selectively deposited by e-beam evaporation on the p-GaN and annealed at 500 \({}^{\circ}\)C for 1 min in nitrogen ambient to form Ag NPs. (**c**) Ag NWs were chemically synthesized according to a previously reported method [19], dispersed in deionized water, and deposited by spin-coating method to obtain a flat film. After photolithography to form TCE region, the Ag NWs were etched using a dilute diluted nitric acid solution of HNO\({}_{3}\)/H\({}_{2}\)O (10:l). For a comparative study, a Ag NW layer without NPs was deposited. To form an Ohmic contact, the coated Ag NW layers were annealed at 150 \({}^{\circ}\)C for 10 min in nitrogen ambient. (**d**) Cr/Au was deposited on TCE and n-GaN by e-beam evaporation to obtain n- and p-pads. To determine the optimal structure for improving the efficiency of LEDs with Ag NW or Ag NW/NP TCEs, the enhancement mechanism first had to be identified. Considering that the penetration depth was estimated as \(\sim\)45 nm for QW-SP coupling at an emission energy of 2.75 eV in the blue LED, the Ag NW or Ag NW/NP TCE was deposited on 45 nm thick p-GaN for coupling between dipoles of QW and LSP of Ag NW/NP. To study the effect of LSP-transverse magnetic (TM) or LSP-transverse electric (TE) light coupling on the LEE in the absence of QW-LSP coupling, the Ag NP, Ag NW, or Ag NW/NP TCE was deposited on a 120 nm thick p-GaN layer. Figure 3a shows the photoluminescence (PL) spectra of InGaN/GaN MQW LEDs with Ag NW, Ag NP, or Ag NW/NP TCEs and 45 nm or 120 nm thick p-GaN layers. QW-SP coupling cannot be expected in the LEDs with a 120 nm thick p-GaN layer. Thus, the efficiency of the LED may be improved by the extraction of TE and TM light. However, when we used NPs alone, the PL intensity decreased. This result indicates that the increase in LEE due to LSP-TM/TE light coupling does not compensate for the absorption of photons in Ag NWs or NPs. However, when the NWs were combined with NPs, the PL intensity was 30% higher than that obtained using Ag NWs alone. This result shows that NPs can improve the LEE for TE/TM polarization.