Investigations on ohmic contact to p-doped gallium nitride

Abstract

In this work, a relatively good ohmic contact (with a specific contact resistance, Rc = 9.80x10-5 I?cm2) to p-doped GaN (~ 2.88 x 1017 cm-3) using Pd(50 nm)/Ni(30 nm)/Au(200 nm) contact has been fabricated. For post-photoresist surface treatment, a N2/Cl2 plasma (5/25 sccm) with a subsequent chemical aqua regia (3HCl: 1 HNO3) treatment has been found to yield a better I-V characteristic than either plasma or aqua regia. It has also been demonstrated that pre-photoresist surface treatment, i.e. N2/Cl2 plasma (5/25 sccm) prior to photoresist coating with a subsequent chemical aqua regia (3HCl: 1 HNO3) treatment, is preferred to post-photoresist plasma treatment. In addition, it has been observed that the ICP and RIE powers for the plasma treatment are critical to obtaining a low specific contact resistance and their optimal values are 500W and 300W, respectively. Lastly, surface roughness of GaN does not seem to have a clear relation with contact characteristic.