Impact of grain-dependent boron uptake on the nano-electrical and local optical properties of polycrystalline boron doped CVD diamond

Abstract

Boron-doped diamond (BDD) films grown by chemical vapor deposition (CVD) exhibit unique electrical and optical properties owing to the non-uniform uptake of boron dopants across grains. This study utilizes scanning probe microscopy and confocal micro- spectroscopy techniques to elucidate the influence of grain-dependent boron incorporation on the nano-electrical and local optical characteristics of polycrystalline BDD. The CVD- grown BDD film contained crystallites up to tens of microns, while the surface comprised 200…800 nm grains. Scanning spreading resistance microscopy (SSRM) revealed significant nanoscale resistance variations among individual grains, attributable to differential boron distributions. No distinct grain boundary features were discernible in SSRM data, likely due to the high boron doping of ~ 3·10 19 cm –3 . SSRM of the Au surface of a BDD/Ti/Pd/Au contact indicated a comparable granular morphology but three orders lower resistance. A network of more resistive grain boundaries was evident, modulated by underlying BDD grain clusters. Photoluminescence spectroscopy showed characteristic bands of nitrogen-vacancy centers and donor-acceptor pairs. Confocal Raman and photoluminescence mapping elucidated substantial spatial heterogeneity in micrometer- scale grains regarding crystal quality, boron and nitrogen concentrations, related to preferential incorporation. The observed peculiarities in BDD’s structural and nano- electrical characteristics stem from inherent growth inhomogeneities and grain-dependent boron uptake influenced by defects and strain fields modifying local chemical potentials. This multifaceted nanoscale examination provides critical insights into optimizing electrical and optical properties of BDD films by controlling synthesis conditions and minimizing defects for tailored performance in electronic, electrochemical, and quantum applications.