Visible and near-infrared luminescence from silicon nanostructures formed by ion implantation and pulse annealing

Abstract

Thermally-grown, 500 nm thick SiO 2 films were implanted with 1.6 × 10 16–1.6 × 10 17 cm −2 Si + ions at 100 and 200 keV. Then the samples were subjected to either rapid thermal annealing at 900–1200°C for 1s or flash-lamp annealing at 1050–1350°C for 20 ms. Photoluminescence (PL) measurements, Raman spectroscopy (RS) and high-resolution transmission electron microscopy (HREM) were employed for sample characterization. Weak room-temperature (RT) visible PL was observed before the transient anneals. RS revealed in these samples a broad band centered at 480 cm −1 indicating the presence of non-crystalline Si inclusions. The initial annealing steps decreased the PL intensity, but after 1200°C, 1 s or 1350°C, 20 ms the PL was found to increase considerably over the red and IR region with a maximum around 830 nm. Simultaneously, the Raman signal at 480 cm −1 diminished and additional scattering near 520 cm −1 arose pointing to the formation of Si nanocrystals. Formation of 2–6 nm Si nanocrystals was directly confirmed by HREM. It is difficult to explain their occurrence by diffusion-limited growth or solid-phase crystallization of α-Si phase inclusions, if any. A model is presented considering the Si nanocrystal formation via segregation of Si atoms from SiO x , rapid percolation-like formation of Si chains or fractals and finally their transformation to Si phase inclusions and nanocrystals. The dramatic increase in PL correlated with the Si nanocrystals formation is considered to support the idea of quantum-confined origin of PL.