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

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 (300degreesC-800degreesC) 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 as-deposited, annealed, and annealed-and-cryogenically treated contacts where the electrical behavior and the surface morphology of each of these conditions were compared.