Electron-energy-loss investigation of hole-plasmon excitation due to thermal indiffusion boron doping of Si(111) surfaces

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Abstract
High-resolution electron-energy-loss-spectroscopy (HREELS) measurements have been performed on Si(111) surfaces heavily p-doped by the decomposition of adsorbed decaborane with subsequent diffusion more than ∼1000 Å below the surface. After thermal decomposition of the decaborane to produce B atoms on the surface the low-energy-electron-diffraction pattern shows a √3 × √3 periodicity due to 1/3 ML of boron in the second complete layer. The HREELS data have two strong features: (1) the B-Si dipole vibrational mode at 96 meV and a broad electronic surface-plasmon mode at ∼100 meV loss energy due to the free carriers in the region below the B-reconstructed surface layer. We have investigated the energy dependence of the plasmon mode in order to determine the possibility of using HREELS to determine the depth profile of the free carriers due to B diffusion into the region ∼50–500 Å below the surface. Unexpectedly, we find that kinematic factors play an important role in the energy range used, 1.5–28 eV, and thus limit the degree of quantitative information that can be obtained about the carrier depth profile from HREELS data in this low-energy range. An approximate depth profile is deduced from the well-established three-layer model (vacuum-surface-bulk layers) after correcting the plasmon peak position for the kinematic factors.