Mechanism of Defect-Impurity Synergy in Laser-Induced Conductive Layer on Single-Crystal Diamond Surfaces

Abstract

As a wide-band gap semiconductor, the formation of conductive layers on diamond surfaces is crucial for overcoming its insulating properties. Laser-induced doping has been demonstrated to be effective in generating low-resistance conductive layers on diamond. However, the underlying mechanism remains poorly understood. This study employs a multiscale characterization approach, including TOF-SIMS, Raman spectroscopy, AFM, and variable-temperature Hall measurements, to propose a novel mechanism for diamond surface conductivity, highlighting the synergistic interaction between defects and impurities. At the microscopic level, vacancies and interstitial atoms form diffusion channels for phosphorus; at the macroscopic scale, defect-induced localized states reduce the carrier activation energy to 0.0192 eV, facilitating hole conduction. Experiments demonstrate that 248 nm laser irradiation, with its higher photon energy, induces a denser defect network, significantly increasing phosphorus doping depth and concentration, resulting in a resistivity as low as 1.1 × 10^-3 Ω·cm. This study systematically investigates the influence of laser parameters on the performance of conductive layers on diamond surfaces and proposes a novel laser-induced conduction mechanism, providing a solid foundation for the doping and conduction theoretical framework of ultrawide band gap semiconductors.

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Laser-induced doping experimental schematic.

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(a, b) Microscope photos and AFM images of diamond surfaces before laser irradiation. (c, d) Microscope photos and AFM images of diamond surfaces after laser irradiation (355 nm, 6.9 J/cm², 2 Hz, and 100 times). (e, f) microscope photos and AFM images of diamond surfaces after laser irradiation (248 nm, 6.9 J/cm², 2 Hz, and 100 times).

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Raman spectrum of the diamond.

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(a) Two-dimensional distribution of phosphorus on the diamond surface by SIMS. (b) Three-dimensional distribution of phosphorus in the diamond by SIMS. (c) SIMS depth profile of phosphorus in the diamond.

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Changes in electrical resistivity under different irradiation times, frequencies, and wavelengths by Hall.

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Temperature dependence of carrier concentration by Hall (same laser parameters: 6.9 J/cm², 2 Hz, and 100 times).

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Schematic diagram of the conductive mechanism.