Interplay of bonding and electronic properties at diamond interfaces
Résumé
Potential discontinuities and spatial profiles govern the electronic properties of elementary devices like Schottky diodes and metal/insulator/semiconductor (MOS) structures. At interfaces between oxygenated diamond and other materials, two situations are examined: (1) Zr Schottky contact; (2) MOS capacitors, mainly using Al2O3 as an insulator.
In the first case, we give two experimental evidences of potential barrier inhomogeneities and/or domains, which almost vanish after annealing at 450°C, with a simultaneous decrease of the homogeneous barrier height of 1.4 eV, analogous to the change in electronic affinity when the oxygen terminations disappear from the surface. This evolution is the same for 4 other metals. The model able to comply with these experimental facts relies on the Mott-Schottky linear relationship which links the barrier height and the electronic affinity at a zero order of approximation, and on a correction term proportional to the charge transfer in interface bonds. This last term is able to justify the reverted slope observed regarding the dependence of the barrier height on the metal work function.
In the second case, a capacitance measurement method is developed in order to show the projected interface states density and Fermi level pinning at the Al2O3 /oxygenated diamond interface of MOS capacitors. Reasons for these results, based on bonding between carbon, adsorbates and insulator atoms, and possible routes to free the interface from this Fermi level pinning are discussed.
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