Optical properties of nanowire structures produced by the metal-assisted chemical etching of lightly doped silicon crystal wafers

Layers of Si nanowires produced by the metal-assisted chemical etching of (100)-oriented single-crystal $p$-Si wafers with a resistivity of 1–20 $\Omega$ $\cdot$ cm are studied by reflectance spectroscopy, Raman spectros-copy, and photoluminescence measurements. The nanowire diameters are 20–200 nm. The wafers are supplied by three manufacturing companies and distinguished by their different lifetimes of photoexcited charge carriers. It is established that the Raman intensity for nanowires longer than 1 $\mu$m is 3–5 times higher than that for the substrates. The interband photoluminescence intensity of nanowires at the wavelength 1.12 $\mu$m is substantially higher than that of the substrates and reaches a maximum for samples with the longest bulk lifetime, suggesting a low nonradiative recombination rate at the nanowire surfaces.