Microstructure and Electrical Properties of Low Temperature Processed Ohmic Contacts to p-Type GaN

Abstract

With Ni/Au and Pd/Au metal schemes and low temperature processing, we formed low resistance stable Ohmic contacts to p‐type GaN. Our investigation was preceded by conventional cleaning, followed by treatment in boiling HNO3:HCl (1:3). Metallization was by thermally evaporating 30 nm Ni/15 nm Au or 25 nm Pd/15 nm Au. After heat treatment in O2 + N2 at various temperatures, the contacts were subsequently cooled in liquid nitrogen. Cryogenic cooling following heat treatment at 600 ·C decreased the specific contact resistance from 9.84·10−4 Ωcm2 to 2.65·10−4 Ωcm2 for the Ni/Au contacts, while this increased it from 1.80·10−4 Ωcm2 to 3.34·10−4 Ωcm2 for the Pd/Au contacts. The Ni/Au contacts showed slightly higher specific contact resistance than the Pd/Au contacts, although they were more stable than the Pd contacts. X‐ray photoelectron spectroscopy depth profiling showed the Ni contacts to be NiO followed by Au at the interface for the Ni/Au contacts, whereas the Pd/Au contacts exhibited a Pd:Au solid solution. The contacts quenched in liquid nitrogen following sintering were much more uniform under atomic force microscopy examination and gave a 3 times lower contact resistance with the Ni/Au design. Current‐voltage‐temperature analysis revealed that conduction was predominantly by thermionic field emission.

Ohmic Contacts to P–GaN Based on the Single–Walled Carbon Nanotubes

“…Nevertheless, from among all contact structures on p-GaN the Au/Ni/p-GaN [8][9][10][11][12][13][14][15][16][17] structure seems to be the most suitable thanks to relatively good values of the specific contact resistance and in the case of very thin layers also thanks to optical transparency.…”

Auger electron spectroscopy of Au/NiO contacts on p-GaN annealed in N2 and O2+ N2 ambients

“…Due to its wide-band gap and the low doping level, low resistivity contacts to p-type GaN are difficult to achieve. A lot of investigations have been made in the last few years, including a variety of metallization schemes and different surface pre-treatments such as cleaning procedures, annealing and sputter treatment [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16].…”

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].…”