Porous Si(1Â 1Â 1) and Si(1Â 0Â 0) as an intermediate buffer layer for nanocrystalline InN films

We report preliminary results on the indium nitride (InN) films grown on porous silicon (PSi) substrates by reactive magnetron sputtering using an indium target. PSi is used as an intermediate layer between silicon and InN and it provides a large area composed of an array of voids. The PSi samples were prepared using photoelectrochemical method on n-type silicon wafer with (1 1 1) and (1 0 0) orientation. To prepare porous structures, the samples were dipped into a mixture of HF:ethanol (1:1) for 5 min with current densities of 50 mA cm−2, and subjected to external illumination with a 500 W UV lamp. The surface morphology and the crystalline structure of the InN films were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD). Structural analysis revealed nanocrystalline structure with crystallite size of 32 ± 0.05 nm and 20 ± 0.05 nm for InN films grown on Si(1 1 1) and Si(1 0 0) orientation, respectively. The optical properties of InN layers were examined by micro-Raman and Fourier transform infrared (FTIR) reflectance spectroscopy at room temperature. Micro-Raman results showed that A1(LO) of hexagonal InN/Si(1 1 1) and InN/Si(1 0 0) have been observed at 588.4 cm−1 and 587.0 cm−1, respectively. From the results of FTIR spectroscopy, the TO [E1(TO)] phonon mode of the InN/Si(1 1 1) and InN/Si(1 0 0) are clearly visible at 472 cm−1 and 470 cm−1, respectively.