Munsik Oh

Silver Nanowire Transparent Conductive Electrodes for High-Efficiency III-Nitride Light-Emitting Diodes.

Silver nanowires (AgNWs) have been successfully demonstrated to function as next-generation transparent conductive electrodes (TCEs) in organic semiconductor devices owing to their figures of merit, including high optical transmittance, low sheet resistance, flexibility, and low-cost processing. In this article, high-quality, solution-processed AgNWs with an excellent optical transmittance of 96.5% at 450 nm and a low sheet resistance of 11.7 Ω/sq were demonstrated as TCEs in inorganic III-nitride LEDs. The transmission line model applied to the AgNW contact to p-GaN showed that near ohmic contact with a specific contact resistance of ~10−3 Ωcm2 was obtained. The contact resistance had a strong bias-voltage (or current-density) dependence: namely, field-enhanced ohmic contact. LEDs fabricated with AgNW electrodes exhibited a 56% reduction in series resistance, 56.5% brighter output power, a 67.5% reduction in efficiency droop, and a approximately 30% longer current spreading length compared to LEDs fabricated with reference TCEs. In addition to the cost reduction, the observed improvements in device performance suggest that the AgNWs are promising for application as next-generation TCEs, to realise brighter, larger-area, cost-competitive inorganic III-nitride light emitters.

Sputter deposition of Sn-doped ZnO/Ag/Sn-doped ZnO transparent contact layer for GaN LED applications

Abstract Sn-doped ZnO/Ag/Sn-doped ZnO (ZAZ) multilayers prepared using sputtering process was employed in GaN-based blue light-emitting diodes(LEDs) as transparent contact layers (TCLs). The ZAZ layer had better optical and electrical properties without any thermal annealing. The ZAZ TCLs improved the current spreading on p-GaN layer and increased the light output power in the large area devices. The efficiency droop was also quite small in the case of adopting a ZAZ TCL in GaN-based LEDs. These results are promising for the development of a ZAZ TCL using sputtering process for GaN LED applications.

Highly reflective Ti/Ag/Pt contacts to p-GaN for high-efficiency GaN-based light-emitting diodes

The authors report highly efficient GaN-based light-emitting diodes (LEDs) fabricated with Ti/Ag/Pt reflective p-type contact. Compared with the reference Ni/Ag/Pt contact, Ti/Ag/Pt contact annealed at optimized thermal annealing condition produced low specific contact resistances of 5.7 × 10−4 Ω cm2, and good optical reflectivity of 88.4% at 450 nm. This is due to the generated interfacial Ti–O layer upon thermal annealing in N2 ambient, which suppress the excessive inter-diffusion between Ag and GaN layers. Consequently, the LEDs fabricated with Ti/Ag/Pt contacts showed 32.6% brighter light output power and nearly the same forward voltages as compared to the reference LEDs fabricated with Ni/Ag/Pt contacts.

High-efficiency GaN-based light-emitting diodes fabricated with identical Ag contact formed on both n- and p-layers

The authors report high-efficiency GaN-based light-emitting diodes (LEDs) fabricated with identical Ag contact formed on both n- and p-layers. Ag contacts thermally annealed at optimized conditions yielded low specific contact resistances of 4.5 × 10(-4) and 9.4 × 10(-4) Ωcm(2), and high optical reflectivity (at 450 nm) of 88.1 and 85.3% for n- and p-contact, respectively. LEDs fabricated with identical Ag contacts formed on both layers showed 31% brighter light output power and nearly the same forward voltages as compared to reference LEDs. This indicates that Ag contact can be used as a reflective electrode for both n- and p-layers, leading to enhanced extraction efficiency and fewer process steps.

Vertical-Injection GaN-Based Light-Emitting Diodes Fabricated With Schottky-Contact Current Blocking Layer

Vertical-injection GaN-based light-emitting diodes (LEDs) fabricated with a Schottky-contact current blocking layer (ScCBL) are reported. The Ar plasma treatment to the heavily Mg-doped p-GaN led to excellent rectifying Schottky behavior, which was found to occur as a result of the suppressed hopping conduction at the contact/p-GaN interface. This could be due to the preferential removal of the Mg dopants by the Ar plasma treatment, as verified by secondary ion mass spectroscopy. Compared with the reference LEDs fabricated with SiO2 CBL, the LEDs fabricated with ScCBL showed an identifying current-voltage curve, while the output power increased 5%, indicating that the ScCBL fabricated with the Ar plasma treatment could be used practically to improve process yields and lower the cost of vertical LEDs.