Eur. Phys. J. Special Topics 228, 689–696 (2019)
https://doi.org/10.1140/epjst/e2019-800188-9

Regular Article

Towards the insulator-to-metal transition at the surface of ion-gated nanocrystalline diamond films

¹ Department of Applied Science and Technology, Politecnico di Torino, 10129 Torino, Italy
² Department of Physics and “NIS” Centre, University of Torino, 10125 Torino, Italy
³ Institute of Electron Devices and Circuits, Ulm University, 89069 Ulm, Germany

^a e-mail: renato.gonnelli@polito.it

Received: 15 October 2018
Received in final form: 11 January 2019
Published online: 3 July 2019

Abstract

Hole doping can control the conductivity of diamond either through boron substitution, or carrier accumulation in a field-effect transistor. In this work, we combine the two methods to investigate the insulator-to-metal transition at the surface of nanocrystalline diamond films. The finite boron doping strongly increases the maximum hole density which can be induced electrostatically with respect to intrinsic diamond. The ionic gate pushes the conductivity of the film surface away from the variable-range hopping regime and into the quantum critical regime. However, the combination of the strong intrinsic surface disorder due to a non-negligible surface roughness, and the introduction of extra scattering centers by the ionic gate, prevents the surface accumulation layer to reach the metallic regime.