Metal/graphene sheets as p-type transparent conducting electrodes in GaN light emitting diodes

Abstract

We demonstrate the use of graphene based transparent sheets as a p-type current spreading layer in GaN light emitting diodes (LEDs). Very thin Ni/Au was inserted between graphene and p-type GaN to reduce contact resistance, which reduced contact resistance from ∼5.5 to ∼0.6Ω/cm2, with no critical optical loss. As a result, LEDs with metal-graphene provided current spreading and injection into the p-type GaN layer, enabling three times enhanced electroluminescent intensity compared with those with graphene alone. We confirmed very strong blue light emission in a large area of the metal-graphene layer by analyzing image brightness.

Graphene transparent electrodes grown by rapid chemical vapor deposition with ultrathin indium tin oxide contact layers for GaN light emitting diodes

“…15 Nevertheless, these attempts were all at the expense of losing transparency (e.g., merely 78% for 1 nm Ni/1 nm Au/monolayer graphene). 14 We note that optical transmission is ultra important for LEDs. Poor transmission not only directly lowers the output power but also transforms the absorbed light to heat, further decreasing internal quantum efficiency.…”

“…Previous graphene-only devices suffered from high forward voltage (V f > 10 V). 12 Other solutions include using interlayers of thin metal 13,14 or ITO nanodots. 15 Nevertheless, these attempts were all at the expense of losing transparency (e.g., merely 78% for 1 nm Ni/1 nm Au/monolayer graphene).…”

“…Obviously, the transmission of 3 nm, 7 nm, and 10 nm ITO is very high, nearly 100% in 550 nm-780 nm wavelength region, slightly descendent for <550 nm, but still quite high compared to other transition layers such as Au or Ni/Au sheets. 13,14 Typically, the transmissions of 3 nm, 7 nm, and 10 nm ITO are 99.9%, 99.6%, and 99.4% at 460 nm and 97%, 96%, and 94.5% at 320 nm, respectively. At 460 nm and 320 nm, monolayer (trilayer) graphene has transparencies of 96.7% (88.2%) and 91.7% (81.9%), respectively.…”

InGaN-based vertical light-emitting diodes with acid-modified graphene transparent conductor and highly reflective membrane current blocking layer

“…However, high temperature deposition might cause metal substrate bending and even chip fracture and failure. Graphene is a promising next-generation material owing to its excellent optical, electrical and thermal properties [8,9] and is anticipated to play an important role in future uses as a functional component in electronic and optoelectronic devices [10], such as transistors [11], integrated circuits, solar cells [12], optical modulators [13] and LEDs [14][15][16][17]. Owing to the large work function gap between graphene and p-GaN, LEDs with graphene as TCL still show degraded electrical characteristics.…”

Capacitive carbon nanotube networks in polymer composites

“…83 lm, corresponding to cutting rate of 663 nm/h for L Prsitine !L 2.5h , 217 nm/h for L 2.5h !L 5h , 206 nm/h for L 5h !L 7.5h , and 178 nm/h for L 7.5h !L 10h. 7 The L shortening also means a greater CNT density per unit area compared with pristine nanotubes in polymer (e.g., 40 wt. %), accounting for increased v C in (Figure 2(a)).…”