The electrical, morphological, and optical properties of heavily boron-doped diamond sheets as a function of methane concentration in the gas phase

Abstract

Boron-doped diamonds (BDD) are known for their excellent properties such as high thermal conductivity, high mobility, low absorption in visible light, and biocompatibility. In this work, we investigated the electrical, morphological and optical properties of heavily boron-doped diamond thin sheets as a function of methane concentration in the gas phase. Free-standing diamond sheets were fabricated using a microwave plasma-assisted chemical vapor deposition. The methane concentration was controlled by adding CH₄ (up to 4%) to the gas phase, while the <strong>/[C] ratio was 20,000 ppm. The samples grown with a higher methane concentration show more defects providing additional conduction paths. As a result, the lowest resistance was observed for the sample with a 4% methane concentration in the gas phase. Morphological studies suggest that a strong increase in the standard deviation of grain size and larger thickness of films is correlated with a higher sp² phase. Moreover, an increase of disordered carbon content is accompanied by a lower transparency of the BDD sheets. This experiment could serve as a stepping stone in the future production of highly conductive large-area boron-doped diamond sheets.