Ohmic contact to nonpolara-plane p-type GaN using Ni/Au

Abstract

In this study, we examined the characteristics of Ni/Au (20 nm/80 nm) ohmic contacts to non-polar a-plane p-GaN as a function of annealing temperature. The current-voltage (I-V) curves were showed an upward curve with annealing when Ni/Au metals were used as ohmic metals to nonpolar p-GaN, which was similar to those of the other crystalline planes. The contact resistivity decreased from 2.36 to 6.95 ' 10 %3 Ω cm 2 . Secondary ion mass spectroscopy showed that the Ga atoms out-diffused from the GaN substrate after annealing at 400 °C, which led to the generation of Ga vacancies. The formation of Ga and N vacancies was found to be a competing process during annealing.

Impact of acceptor concentration on the resistivity of Ni/Au p‐contacts on semipolar (20–21) GaN:Mg

“…Nevertheless, the calculated value for the sample with II/III ratio of 0.4 × 10 −2 is shown for a rough comparison. For a II/III ratio of 1.6 × 10 −2 , a minimum ρ c of 2.4 × 10 −3 Ω cm 2 could be obtained, which is comparable with results reported on a ‐plane and m ‐plane , but one to two orders of magnitude higher than the best reported values for c ‐plane . In Ref.…”

“…To achieve ohmic contacts, a thin highly doped p ++ ‐GaN cap layer is typically necessary. Although many studies exist for contacts on c ‐plane GaN:Mg, there are only a few studies on ohmic contacts on nonpolar nitrides and semipolar nitrides .…”

Graded electrical breakdown method for obtaining excellent ohmic contact on nonpolar ($11\bar{2}0$) p-GaN

“…For nonpolar p-GaN, however, an ohmic contact with excellent linearity could not be easily obtained. 12) This is due to the large work-function mismatch between p-GaN and metal, where the expected Schottky barrier height (¯B) is as high as ³2.0 eV according to the Schottky-Mott theory, and to the low carrier concentration (N) of ³10 17 cm ¹3 . Furthermore, our group 13) showed that, owing to the presence of a high density of surface states in the epitaxial nonpolar p-GaN, the surface Fermi level (E F ) is even pinned to the 1.9 eV position above the valence band (E V ), i.e., the formation of ohmic contacts via the use of large-work-function metals, such as Pt, Pd, and Ni, will be difficult.…”