Sub-bandgap absorption and structural properties of selenium-hyperdoped silicon after pulsed laser annealing

The formation of impurity sub-band states in selenium-hyperdoped silicon after pulsed laser annealing was investigated. Si samples were implanted with Se⁺ ions in single- and multi-energy regimes with dopant concentrations of 0.4– 2.2 at. %, followed by pulsed laser annealing at energy densities of 0.55–2.5 J/cm². Depth profiles of the dopant concentration, the degree of crystallinity, and the fraction of Se atoms occupying substitutional lattice sites were determined by Rutherford backscattering spectrometry in channeling mode. The formation of sub-band states was confirmed by scanning tunneling spectroscopy. The absorption spectra show a pronounced broad sub-band absorption band with a maximum at ~0.45–0.55 eV and a width of ~0.5 eV. It was found that the sub-band absorption intensity increases with the concentration of substitutional Se atoms, although this dependence is nonlinear. The optimal structural parameters (maximum crystallinity and substitutional Se fraction) are achieved after pulsed laser annealing at 1.5–2.5 J/cm²; however, the sub-band absorption intensity varies nonmonotonically and does not strictly correlate with these structural characteristics. These findings are relevant for the design of optoelectronic devices based on hyperdoped silicon with controllable sub-band absorption characteristics.

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