Interfacial reactions to form high-barrier-height ITO-based Schottky contacts on p-type GaN using a Ti interlayer

We report the development of high-barrier-height and transparent Ti/ITO Schottky contacts on p-GaN for optoelectronic and transparent electronic devices. The Schottky barrier heights (SBHs) and ideality factors estimated using the current–voltage characteristics were in the ranges of 0.36–0.39 eV and 1.74–2.07, respectively, depending on the annealing temperature. However, the barrier inhomogeneity and modified Richardson plot methods yielded much larger SBHs in the range of 0.82–1.18 eV. At 560 nm, the transmittance of the Ti/ITO samples was in the range of 47.4–89.9%. The Ga 2p core levels obtained from the X-ray photoemission spectroscopy (XPS) of the interface regions of the ITO/Ti/GaN samples shifted toward higher or lower energies, depending on the annealing temperature. The normalized N/Ga atomic ratio showed that N and Ga vacancies were formed at the p-GaN surface region at 300 and 500 °C, respectively. The XPS Ti 2p, N 1s, and O 1s core level results showed the formation of interfacial TiN and TiO2 phases at 300 and 500 °C, respectively. The elemental mapping results obtained using scanning transmission electron microscopy (STEM) demonstrated the outdiffusion of Ga atoms in the sample annealed at 500 °C. On the basis of XPS and STEM results, the dependence of the SBHs on the annealing temperature is described and discussed. •We develop transparent and high barrier-height Ti/ITO Schottky contacts on p-GaN.•Schottky barrier heights characterized with barrier inhomogeneity and modified Richardson plot.•Ti/ITO contacts show a large Schottky barrier of 1.18 eV when annealed at 300 °C.•Ti/ITO samples show a transmittance of 89.9% at 560 nm when annealed at 500 °C.•XPS and STEM results show that TiN phase is responsible for increased Schottky barrier.