Impact of surface treatment on metal-work-function dependence of barrier height of GaN-on-GaN Schottky barrier diode

The impact of surface treatment on Schottky contacts on a GaN-on-GaN epitaxial layer was comprehensively investigated by combining X-ray photoelectron spectroscopy (XPS) at each step of the treatment process and electrical measurements on Schottky barrier diodes. XPS showed that a photolithography process on a GaN surface reduced the surface oxide and band bending and that the subsequent HCl-based treatment reduced them further. Electrical measurements indicated that HCl treatment after photolithography affected the metal-work-function, ϕM, dependence of the Schottky barrier height, ϕB, resulting in an increase in the slope factor compared with that of the samples without HCl treatment. It is highly likely that the reduction in interface disorder by the chemical treatment led to a reduction in the interface state density at the metal/GaN interface. On the basis of the obtained ϕB–ϕM plots, the charge neutrality level was measured experimentally to be 5.0 eV from the vacuum level and 0.9 eV from the conduction band edge, while the electron affinity was measured to be 4.1 eV.