Surface transfer doping of diamond

Abstract

The electronic properties of many materials can be controlled by introducing appropriate impurities into the bulk crystal lattice in a process known as doping. In this way, diamond (a well-known insulator) can be transformed into a semiconductor1, and recent progress in thin-film diamond synthesis has sparked interest in the potential applications of semiconducting diamond2,3. However, the high dopant activation energies (in excess of 0.36 eV) and the limitation of donor incorporation to (111) growth facets only have hampered the development of diamond-based devices. Here we report a doping mechanism for diamond, using a method that does not require the introduction of foreign atoms into the diamond lattice. Instead, C60 molecules are evaporated onto the hydrogen-terminated diamond surface, where they induce a subsurface hole accumulation and a significant rise in two-dimensional conductivity. Our observations bear a resemblance to the so-called surface conductivity of diamond4,5,6,7,8 seen when hydrogenated diamond surfaces are exposed to air, and support an electrochemical model in which the reduction of hydrated protons in an aqueous surface layer gives rise to a hole accumulation layer6,7. We expect that transfer doping by C60 will open a broad vista of possible semiconductor applications for diamond.

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Figure 1: Conductance of different substrates upon evaporation of C60 in ultrahigh vacuum.
Figure 2: Schematic representation of the surface transfer doping of intrinsic diamond by C60.
Figure 3: Comparison between experiment and simulation of the two-dimensional conductivity of hydrogen-terminated diamond as a function of C60 coverage.
Figure 4: Reduction of the ‘band offset’ Δ (see Fig. 2) between the diamond valence band maximum and the C60 LUMO with increasing C60 coverage.

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Acknowledgements

We acknowledge A. Hirsch for the gift of C60 and fruitful discussion. Partial financial support by the Deutsche Forschungsgemeinschaft is also gratefully acknowledged.

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Correspondence to J. Ristein.

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Strobel, P., Riedel, M., Ristein, J. et al. Surface transfer doping of diamond. Nature 430, 439–441 (2004). https://doi.org/10.1038/nature02751

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