The Raman scattering intensity of the 1100 cm−1 polarized band, which appears on the addition of Na2O to SiO2 glass, reaches a maximum at the disilicate composition. The intensity of the polarized band at 950 cm−1 increases sharply as the Na2O concentration increases above 30 mole %. These data were interpreted by normal mode calculations and by IR and Raman intensity calculations for the silicate anion structural units: SiO4 isolated tetrahedra, Si2O7 dimers, Si2O6 chain links, Si2O5 sheet units, and Si2O4 framework units. According to these simplified models, the polarized high frequency band is due to symmetric stretching of Si–O− nonbridging bonds and the frequency increases with degree of polymerization of the tetrahedra. The previous assignments of the 1100 cm−1 band to the symmetric stretch of tetrahedra containing one nonbridging oxygen and of the 950 cm−1 band to the symmetric stretch of tetrahedra containing two nonbridging oxygens were confirmed. The other main feature of the alkali silicate glasses, an intense polarized band in the range of 400–600 cm−1, was shown to be a mixed stretching bending mode of the Si–O–Si bridging bond. The model also accounts for the loss of intensity of the high frequency band with increasing degree of silica polymerization.
Metal-organic chemical vapor deposition growth of GaAs on Si was studied using the selective aspect ratio trapping method. Vertical propagation of threading dislocations generated at the GaAs∕Si interface was suppressed within an initial thin GaAs layer inside SiO2 trenches with aspect ratio >1, leading to defect-free GaAs regions up to 300nm in width. Cross-sectional and plan-view transmission electron microscopies were used to characterize the defect reduction. Material quality was confirmed by room temperature photoluminescence measurements. This approach shows great promise for the fabrication of optoelectronic integrated circuits on Si substrates.
A novel planar separate absorption, charge sheet, grading and multiplication avalanche photodiode (APD) structure incorporating a partial charge sheet in the device periphery is described, which allows for straightforward fabrication of APD devices without the use of guard rings. Metalorganic chemical vapor deposition grown, Zn-diffused InP/InGaAs APD devices have been fabricated. High dc gains well in excess of 100 and a low primary dark current of 0.1 nA at 0.99 of the breakdown voltage VB have been measured for a 40-μm-diam device. The receiver sensitivity for a bit error rate of 10−9 at a bit rate of 400 Mbit/s was −41 dBm. The −3 dB electrical bandwidth was 2.5 GHz, and the gain-bandwidth product was 30 GHz.
Ferric iron-substituted sodium metaphosphate and calcium metaphosphate glasses exhibit a very weak luminescence that can be observed under laser excitation. Broad emission bands at 16 000 cm-' and at 12 000 cm-' are assigned to the 4Ti+6Ai transitions of Fe3f in four-and six-coordinated sites respectively. The interpretation is supported by crystal Jeld theory calculations based on known absorption spectra of Fe3+.AKIOCIS methods have been used to
InGaAsP/InP quantum well (QW) ridge waveguide lasers emitting nominally at 1310 nm have been ‘‘blue-shifted’’ selectively (as much as 70 nm) on a full 50-mm-diameter wafer after growth. P+ ion implantation at 1 MeV, 200 °C through a variable thickness SiO2 mask was used to induce various degrees of QW intermixing after postimplantation annealing at 700 °C. Irrespective of the amount of intermixing induced (blue shift), all fabricated devices exhibited 20–25 mA lasing threshold current and 0.25–0.30 W/A differential quantum efficiency. Device reliability was equivalent to standard (nonimplanted) lasers when the wavelength shift was 35 nm or less, corresponding to predicted lifetime in excess of 25 years while operating cw at 25 °C. The performance and reliability data clearly indicate that the concentration of residual defects introduced in the active region by the implantation/annealing process is negligibly small. The present results, which are a product of a straightforward fabrication process, suggest the possibility of manufacturing high-reliability, low-cost, monolithically integrated optoelectronic chips containing, for example, selectively tuned lasers, optical amplifiers, modulators, and waveguides.
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