Environmental and thermal aging of Au/Ni/p-GaN ohmic contacts annealed in air

Abstract

Cross-plane electronic and thermal transport properties of p-type La0.67Sr0.33MnO3/LaMnO3 perovskite oxide metal/semiconductor superlattices J. Appl. Phys. 112, 063714 (2012) Polarization Coulomb field scattering in In0.18Al0.82N/AlN/GaN heterostructure field-effect transistors J. Appl. Phys. 112, 054513 (2012) Modulation doping to control the high-density electron gas at a polar/non-polar oxide interface Appl. Phys. Lett. 101, 111604 (2012) Ultra low-resistance palladium silicide Ohmic contacts to lightly doped n-InGaAsIn recent years, Au/Ni/p-GaN ohmic contacts annealed in air have been studied extensively because they provide low specific contact resistances and high transparency. In this article we focus on the environmental and thermal degradation that we have observed in these contacts. When the contacts were not protected from the environment, degradation of the contacts always occurred over a period of days, and after sitting 30 days in the laboratory at room temperature, the current-voltage characteristics of the originally ohmic contacts were nonlinear and the contacts were significantly more resistive. To pinpoint the degradation mechanism, samples were stored at room temperature in dry nitrogen, dry oxygen, dry air, air saturated with water vapor, nitrogen gas saturated with water vapor, or vacuum. These experiments revealed that water vapor was the cause of the room temperature degradation. Since no change in the sheet resistance of the p-type GaN was observed upon aging, four point probe measurements and x-ray photoelectron spectroscopy depth profiles were carried out to determine the interaction between water vapor and the p-type NiO present in the annealed contact metallization. The measurements indicated that hydroxyl groups were incorporated in the NiO, leading to a reduction in its conductivity and presumably a decrease in its hole concentration. Aging studies at 200°C further revealed poor thermal stability of the contacts not only in water vapor but also in nitrogen gas and vacuum, and this degradation was again linked to a degradation in the conductivity of the NiO component of the contact metallization.

Contacts to AlGaN for UV Detectors

“…The thin Ni/Au contacts annealed in air have been used by some of the solar blind detector program participants in their devices (at Northwestern), and we have published information on the environmental and thermal stability of the contacts [Wang02]. Through our study of the contact stability, we are also able to shed more light on the mechanism for the surprisingly low resistance of these contacts.…”

Mechanism investigation of NiOx in Au/Ni/p-type GaN ohmic contacts annealed in air

“…To investigate the ohmic mechanism, microstructural characterization and thermal aging of Au/Ni contacts with p-type GaN annealed in air were reported on. [9][10][11] These reports suggested that the formation of crystalline p-type NiO plays an important role in lowering ohmic-contact resistance. However, by directly depositing a p-type NiO layer on the p-type GaN using a sputter-deposition technique, this contact did not provide specific-contact resistance lower than 10 Ϫ2 ⍀-cm 2 .…”

Improving the Ohmic Properties of Au/Ni–Mg/P–GaN Contacts by Adding Swcnt Metallization Interlayer Between Metal and P–GaN Layers

“…However, the best contact structure to p-GaN seems to be the Au/Ni structure, namely because of the relatively good values of contact resistance and in the case of very thin layers also thanks to its optical transparency. It was found that annealing of such a thin Ni/Au bilayer in air brings about a change of Ni into NiO, diffusion of Au into the interface and at the same time an improvement in the transparency of the metallization layer [2][3][4][5][6][7].…”