Thermal stability of Ni/Ag contacts on p‐type GaN

Abstract

Contact technology remains an important factor for electronic and optical devices in the field of wide band gap semiconductors. To fabricate reliable, efficient, high performance devices and circuit, it is essential to develop high quality and thermally stable contacts to GaN-based material. Making low-resistance ohmic contact is difficult for wide band gap semiconductors, especially p-GaN due to difficulty in achieving high carrier concentration, and the absence of suitable metals which have a work function larger than the bandgap and electron affinity of GaN. In this work, we report on the thermal stability and morphological investigation of Ni/Ag contacts on p-GaN. Different annealing temperatures (300 °C -800 °C) were investigated, as thermally stable metal-semiconductor contacts are essential for high quality devices. Cryogenic cooling after heat treatment was also performed to determine the effects of this treatment on the characteristics of the contacts. Specific contact resistivity (SCR) determined using transmission line method (TLM) and scanning electron microscopy (SEM) measurements were carried out to the asdeposited, annealed, and annealed-and-cryogenically treated contacts where the electrical behavior and the surface morphology of each of these conditions were compared.

NiO removal of Ni/Au Ohmic contact to p-GaN after annealing

“…In order to make reliable devices, specific contact resistance must be decreased to under 10 −4 Ω•cm 2 . But to p-GaN, due to high activation energy (∼170 meV) of the deep Mg acceptor [2] , those grown by MOCVD (metalorganic chemical vapor deposition) or MBE (molecular beam epitaxy) can hardly achieve a doping density higher than 1 × 10 18 cm −3 [3] ，and its work function is very high, so it is still a big challenge to make applicable p-doped Ohmic contacts.…”

Nanometer sized Ni-dot/Ag/Pt structure for high reflectance of p-type contact metal in InGaN light emitting diodes

“…11,12 In an attempt to resolve the peeling off and high contact resistance problems, a Ni layer has been inserted between the p-GaN surface and the Ag coating. [13][14][15][16] Although introduction of Ni layer improves the adhesion and decreases the contact resistance, it has a side effect of degrading the overall reflectivity from Ag coated p-GaN surface. We suspect that by using nanometer sized "Ni-dots" instead of Ni thin film layer, the reflectivity from Ag/Ni/p-GaN surface can be significantly improved while maintaining good adhesion and low contact resistance of Ag coating.…”

InGaN/GaN light-emitting diodes : from modeling to their hybrid applications with novel nanomaterials

“…As a result, high contact resistance is observed when silver is directly laid onto the p-GaN surface, which triggers the deterioration both electrically and optically over time [98]. Thus, to address the aforementioned issues, a very thin Ni layer can be deposited onto the p-GaN surface before depositing Ag [99,100]. This thin transparent layer forms an oxide layer after the annealing process in the O2 environment, thus enhancing the adhesion of silver to p-GaN and decreasing the agglomeration and facilitating the formation of ohmic contact [101].…”