The Si/SiO2 superlattices were prepared by a molecular beam deposition method, high temperature furnace annealing (1100 °C), and back-side Si wafer etching in tetramethyl ammonium solution. Transmission electron microscopy and Raman spectroscopy show that the layered structure is not preserved during high temperature treatment. The etching of the substrate increases photoluminescence of the Si/SiO2 material. Optical waveguiding was realized for the free-standing sample demonstrating its reasonable optical quality and providing the optical parameters.
A Raman and photoluminescence study of a thermally annealed free-standing film of silica containing Si nanocrystals is reported with emphasis on laser-induced thermal effects. The Si-rich silica film on a Si substrate was prepared by a molecular beam deposition method and annealed at 1150 °C for 1 hour in an oven, which promoted Si nanocrystals. Then the Si substrate was partially chemically etched producing free-standing film areas with typical dimensions of 2
mm x 2 mm and thickness of 1.4 μm. For the free-standing film, we observed laser-induced (Ar+ laser at 488 nm) thermal effects on the light-emitting and optical properties. In fact, the light emission dramatically increases with the laser intensity, up to 4 orders of magnitude at 840 nm when the laser power increases from ~100 to 200 mW, and the absorption coefficient rises considerably as well. The anti-Stokes to Stokes Raman intensity ratio suggests a very high temperature of the free-standing silica film containing Si nanocrystals (~1200 K) upon exposure to a laser power of 100 mW focused to a ~40 μm spot, and the temperature probably rises up to ~2000 K for exposure to a laser power of 200 mW. The light emission measured at the high excitation powers is similar to blackbody radiation although some quantitative deviations occur for the temperature dependence. The Ar+ laser annealing strongly increases the crystalline Raman peak showing that thermal annealing at 1150 °C does not finish structural reorganization of the SiOx material. In the waveguiding detection geometry, the spectral narrowing of the photoluminescence is observed and used to estimate the refractive index.
Room temperature (RT) electroluminescence (EL) was obtained for the first time from Mn enriched Si/SiO2 structure. Si+ or Ar+ stimulated knock-on implantation through 20 nm Mn film with the subsequent annealing was used for EL device fabrication. Devices exhibit bright emission band at the 2.06 eV. The position does neither depend on implanted ion dose nor annealing procedure. EL is visible by naked eye even at current density as low as 1.5x10-6 Acm-2. Continuous wave external quantum efficiency 1.1x10-3 and power efficiency 1.5x10-5 have been achieved.
Liquid phase epitaxy (LPE) has been carried out from the mixed Ga+Bi solution of different thickness to improve GaAs epilayer surface morphology and the growth process control. The difference between thin and thick solutions has been demonstrated. The process occurring during epitaxy of GaAs layers growth in a non-stationary LPE system from a molten Ga-Bi solution has been studied. Results obtained from thin and thick liquid phase epitaxy has been compared with the diffusion limited compound semiconductor epitaxial growth model. The results revealed that there are two anomalous kinetics growth zones of solvent composition in which the growth rate is unpredictable by diffusion theory of LPE. A model of the LPE growth from Ga-Bi solutions has been suggested, that take into account complex shape of the liquids curve of the Ga-Bi-As system and changes in the mass transfer process occurring in the microinhomogeneous liquid phase. Electrical and optical property of GaAs epitaxial layer grown from mixed Ga-Bi solvent was studied and discussed. The results from two laboratories that used different experimental methods have been compared.
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