VISIBLE AND NEAR-INFRARED LUMINESCENCE FROM SILICON NANOSTRUCTURES FORMED BY ION-IMPLANTATION AND PULSE ANNEALING

Thermally-grown, 500 nm thick SiO2 films were implanted with 1.6 x 10( 16)-1.6 x 10(17) cm(-2) Si+ ions at 100 and 200 keV. Then the samples were subjected to either rapid thermal annealing at 900-1200 degrees C for 1s or flash-lamp annealing at 1050-1350 degrees C for 20 ms. Phot oluminescence (PL) measurements, Raman spectroscopy (RS) and high-reso lution transmission electron microscopy (HREM) were employed for sampl e characterization. Weak room-temperature (RT) visible PL was observed before the transient anneals. RS revealed in these samples a broad ba nd centered at 480 cm(-1) indicating the presence of non-crystalline S i inclusions. The initial annealing steps decreased the PL intensity, but after 1200 degrees C, 1 s or 1350 degrees C, 20 ms the PL was foun d to increase considerably over the red and IR region with a maximum a round 830 nm, Simultaneously, the Raman signal at 480 cm(-1) diminishe d and additional scattering near 520 cm(-1) arose pointing to the form ation of Si nanocrystals, Formation of 2-6 nm Si nanocrystals was dire ctly confirmed by HREM. It is difficult to explain their occurrence by diffusion-limited growth or solid-phase crystallization of alpha-Si p hase inclusions, if any. A model is presented considering the Si nanoc rystal formation via segregation of Si atoms from SiOx, rapid percolat ion-like formation of Si chains or fractals and finally their transfor mation to Si phase inclusions and nanocrystals, The dramatic increase in PL correlated with the Si nanocrystals formation is considered to s upport the idea of quantum-confined origin of PL.