Characteristics of Ni-Based Bi-Layer Contacts on GaN

GaN-based materials have been the subject of intensive research recently for blue and ultraviolet light emission and high temperature/high power electronic devices. Ohmic contacts with low contact resistance are essential in improving the electrical and optical performances of the devices. A wide variety of contact metallizations have been reported for p-GaN, including the standard Ni/Au as well as Ni. Different surface pretreatments have been investigated to lower the contact resistivity. To employ metal layers as a reliable ohmic contact on GaN, it is essential to understand the thermal stability of metal-GaN contact in addition to developing low resistance ohmic system. In this paper, we report on the characteristics of Ni/Ag bi-layer contacts on p-type GaN. The structural and electrical stability of the contacts at various annealing temperatures (480°C – 780°C)were investigated. Changes in the surface morphology of the contacts on annealing were examined using scanning electron microscopy (SEM). Specific contact resistivity and barrier height, determined using transmission line method (TLM) and current-voltage (I-V) measurements were calculated.