High-transparency Ni/Au ohmic contact to p-type GaN

Abstract

In this study, a very thin Ni/Au bilayer metal film was prepared by electron beam evaporation and thermal alloying to form ohmic contact on p-type GaN film. After thermal alloying, the currentvoltage (I-V) characteristic of Ni/Au contact on p-type GaN film exhibited ohmic behavior. The Ni/Au contacts showed a specific contact resistance of 1.7ϫ10 Ϫ2 ⍀ cm 2 at an alloying temperature of 450°C. In addition, the light transmittance of the Ni/Au ͑2 nm/6 nm͒ bilayer on p-type GaN was measured to be around 85% at 470 nm. These results suggest that a suitable metallization technology for the fabrication of light emitting devices can be achieved.

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

“…1 Ni-, Au-or Pt-based metal electrodes have been used to reduce contact resistance. 2,3 However, due to the difficulty in achieving heavily doped p-type GaN, current spreading over a large area cannot be achieved by the use of these opaque metal electrodes. Alternatively, tin-doped indium oxide (ITO) has been employed as a transparent conducting electrode for ptype GaN.…”

“…Very thin Ni/Au was inserted between graphene and p-type GaN to reduce contact resistance, which reduced contact resistance from $ 5:5 to $ 0:6X= cm 2 , 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.…”

Fabrication and characterization of GaN-based light-emitting diodes without pre-activation of p-type GaN

“…On the other side, reliable p-type ohmic contacts with high optical transmittance are technologically important for realizing high-performance GaN-based LEDs. Ni/Au contact is usually used as semitransparent ohmic electrodes as well as current spreading layer for GaNbased LEDs [14,15]. However, the light transmittance of the Ni/Au contact is relatively low.…”

Transparent ZnO-Based Ohmic Contact to p-GaN

“…Among the investigated metallizations that would allow low-resistivity contact to p-GaN, oxidized Ni/Au bilayer was reported to give the lowest operating voltages [1][2][3]. For the transparent p-type electrode, optimization of Ni/Au metallization via reducing its thickness [4,5] has been achieved, however, at the cost of increase of the specific contact resistance. Another approach for obtaining effective current-spreading layer, providing low-resistivity contact to p-type GaN in conjunction with efficient and uniform light emission, would be to make the p-type contact/window layer from a transparent conducting oxide (TCO).…”