Gabriel Munro-Ludders1,Saurabh Vishwakarma1,David Smith1,Robert Nemanich1,Franz Koeck1
Arizona State University1
Gabriel Munro-Ludders1,Saurabh Vishwakarma1,David Smith1,Robert Nemanich1,Franz Koeck1
Arizona State University1
Ohmic metal contacts to n-type diamond have historically posed a challenge to the fabrication of diamond devices, due to the formation of a rectifying Schottky barrier, which limits the practicality and scope of diamond devices. Nitrogen-doped nanoCarbon films have recently been explored as ohmic interface layers to enable low-resistance ohmic contact with N-type diamond [1]. In this work the electronic interface between nitrogen-doped nanoCarbon interlayers and metals is investigated using photoelectron spectroscopy and transmission electron microscopy, to determine the mechanism of ohmic contact. <br/> <br/>Titanium and molybdenum layers were deposited on nanoCarbon films, and each respective metal/nanoCarbon interface was characterized via X-ray Photoelectron Spectroscopy (XPS) and Ultraviolet Photoelectron Spectroscopy (UPS). The n-type SBH was determined to be Φ<sub>B</sub> = 3.7 eV and Φ<sub>B</sub> = 4.1 eV for the titanium-nanoCarbon and molybdenum-nanoCarbon interfaces, which indicates a partial pinning of the fermi level. Characterization via TEM and electron energy loss spectroscopy reveal the presence of ~4 nm diameter sp<sup>3</sup>–bonded diamond grains surrounded by a matrix of sp<sup>2</sup> bonded carbon, indicating a mixed phase material with non-crystalline states. Two models of the contact mechanism, contingent on the density of unfilled surface states after metal deposition, are proposed to understand the ohmic contact mechanism. A sufficiently low surface state density coupled with a high inter-bandgap density may reduce band bending and allow for flat-band contact by filling surface states, unpinning the fermi level. Alternatively, hopping-type conduction near the Fermi level through π*-bonded states into the conduction band may also reduce the effective SBH. <br/> <br/>Future work will investigate the electronic interface between nanoCarbon interlayers and n-type diamond substrates, to enable ohmic contact with n-type single-crystalline diamond. Switching between pinned and unpinned contact regimes through modulating the inter-bandgap state density via modifying morphology, doping concentration, and non-carbon chemical composition in the film also presents an avenue for future investigations. <br/> <br/>Research supported by the NSF under Award No. 2003567 and by ULTRA, an Energy Frontier Research Center funded by the DOE Office of Science, Basic Energy Sciences (BES) under Award No. DE-SC0021230.