Abstract:
The conductivity of nominally undoped single-crystal diamond films grown epitaxially by chemical vapor deposition on a heavily boron-doped $p^4$-type diamond substrate has been studied. The conductivity of the films has been determined by the boron acceptor impurity. The temperature dependence of the conductivity in the temperature range of $300$–$500$ K obeys the activation law, but the activation energy significantly exceeds the ionization energy of boron acceptors of $\varepsilon_i = 0.37$ eV. It has been found that the acceptors are strongly compensated. This leads to the appearance of a random potential with a large amplitude of $\gamma\approx 0.2$ eV, leading to a large increase in the activation energy $\varepsilon_i +\gamma$. The reason for the appearance of the strong random potential has been attributed to the self-compensation of boron impurities by nitrogen atoms during the chemical vapor deposition growth of diamond films on the heavily doped substrate.
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