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Core excitons and conduction-band structures in layered semiconductor black phosphorus

1984; American Physical Society; Volume: 30; Issue: 8 Linguagem: Inglês

10.1103/physrevb.30.4555

1095-3795

M. Taniguchi, S. Suga, M. Seki, Akira Mikuni, Seiji Asaoka, Hiroshi Kanzaki, Yuichi Akahama, S. Endo, Shin‐ichiro Narita,

Crystal Structures and Properties

Core-level reflectance and photoelectron total-yield spectra of the layered semiconductor black P have been measured by use of the highly polarized synchrotron radiation. The $2p$ core spectra have shown strong anisotropy for $\stackrel{\ensuremath{\rightarrow}}{?}\ensuremath{\parallel}\stackrel{\ensuremath{\rightarrow}}{\mathrm{a}}$ and $\stackrel{\ensuremath{\rightarrow}}{?}\ensuremath{\parallel}\stackrel{\ensuremath{\rightarrow}}{\mathrm{c}}$. The remarkably sharp doublet structures observed at the $2p$ core threshold are assigned to the spin-orbit partners of the $2p$ core excitons associated with flat regions of the quasi-two-dimensional conduction bands on the basis of band calculation. The binding energies of the core excitons are evaluated to be 0.34-0.4 eV. Other structures above the $2p$ core threshold are assigned to the transitions from the $2p$ core levels to particular flat regions of conduction bands. Their energy positions and the strong anisotropy are consistently explained. It is found that the $2s$ core spectra are much broader than the $2p$ core spectra and they are fairly well described on the basis of the density-of-states picture. The significant difference of the spectral features between the $2s$ and $2p$ core spectra are explained by taking the special $\mathrm{sp}$ hybrids of the covalent bonding structure in black P into account.