Effects of Pre-and Post-surface Treatment on Ni-based p-GaN Ohmic Contact

Before the deposition of Ni/Au contact onto p-GaN,a surface treatment with aqua regia,HCl and buffer HF was carried out.After annealing in O2 atmosphere,the I-V and morphological characteristics of the samples with and without different pre-Surface treatments were measured and compared.The contact resistance of the samples without pre-surface treatment was found to be the lowest,while the surface conditions indicated the electrolyte left on the surface after the pre-treatment may damage the current characteristic and stability of the contacts.Auger electron spectroscopy(AES) depth profiles were measured to detect the distribution of different elements,thus it was found the oxidation on the GaN surface can provide partial oxygen in forming NiO during annealing,resulting in a clean surface,so the pre-surface treatment of removing oxidation layer is unnecessary for Ni-based contacts.Then the samples were dipped in 10% oxalic acid to remove NiO layer on the surface,I-V curves review an obvious decrease in the specific contact resistance.A test with surface X-ray Photonic Spectroscopy(XPS) showed that Ni signal intensity in the contact was lower than those without oxalic acid treatment,while Au signal intensity increased,indicating the successful removal of highly resistive NiO layer.It can actually improve the properties of the contacts.