Ohmic graphite-metal contacts on oxygen-terminated lightly boron-doped CVD monocrystalline diamond

The group of Jocelyn Achard LSPM in collaboration with the university del Salento in Italy had recently published interesting results concerning the developmet of a process to obtain ohmic contacts on oxygen-terminated lightly boron-doped CVD monocrystalline diamond films. Samples were contacted by Ti/Au metallic pads in the transmission line model (TLM) configuration. The electric contacts were placed onto a mesa structure produced on the CVD boron-doped layer. One of the samples was additionally implanted with helium ions at 10 keV in order to induce the formation of a graphitic layer underneath the diamond surface before contacting so as to improve electrical conduction. The electrical performance of both devices was characterized by the TLM method and compared. As a result, the
sample with metallic electrodes exhibited a small and non-linear electrical conduction, while the graphitic/ metallic contacts showed an ohmic behaviour with an estimated specific contact resistance as low as 3.3 × 10−4 Ω·cm2 for a doping level of a few 1017 cm−3 . This approach opens the way to more efficient ohmic contacts on intrinsic or low-doped diamond that are crucial for the development of electronic devices and detectors.

M. De Feudis,V. Mille, A. Valentin, O. Brinza, A. Tallaire, A. Tardieu, R. Issaoui,J. Achard,
Laboratoire des Sciences des Procédés et des Matériaux, CNRS, Université Paris 13, Sorbonne Paris Cité, 93430 Villetaneuse, France
Dipartimento di Matematica e Fisica, Università del Salento, 73100 Lecce, Italy

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Left : CVD monocrystalline diamond after a He ion implantation treatment. This treatment (performed with a ring-mask) induced the diamond graphitization in the central part (black color), while the external part remained intrinsic diamond (the yellow color is related to the diamond substrate). top-rigth : same diamond sample after the manufacturing of Titanium/Gold metallic contacts (order of micrometers). Bottom-right : zoom on the central area.