Inducing efficient visible light emission from silicon (Si) and understanding the underlying physics have long defined fascinating scientific and technological challenges. We present a comprehensive study on the origin and nature of red to ultraviolet (UV) light emission from Si quantum dots (QDs). We report the strongest quantum confinement (QC) effects to date and find that: (i) light emission can be stable in ambient and continuously tunable from the red to the UV through a single mechanism, i.e., QC, (ii) the energy gap increases from QC with decreasing size (E<sub>g</sub>(d)- 1.14 ∝1/4<sup>1.4</sup>) to energies significantly greater than previously observed (3.80 eV), (iii) the lowest optical transition remains predominantly indirect despite strong QC in small QDs (~14 Å diameter), and (iv) these properties can apply to QDs with and without a surface oxide layer. These results agree well with calculations that go beyond effective mass approximations. Visible light emission can also result from localized traps and may be mistaken for quantum confined emission.
We present and discuss results outlining the use of fullerenes for optoelectronics and photonics. These applications are particularly compelling with the observation of such promising properties as photoluminescence, electroluminescence, large nonresonant optical nonlinearity, and superconductivity. We focus on nonlinear optical properties and their application to high- speed integrated all-optical switching. We present measurements on the dispersion and dynamics of the nonlinear optical coefficients in the near infrared and the figure of merit for photonic switching, indicating very favorable results. The first demonstration of photonic switching using fullerene thin films as the nonlinear medium is presented. Our results show many advantages of fullerenes and fullerene devices, including the simplicity of processing into guided wave structures for nonlinear integrated optics, large nonlinear coefficients, effectively nonlatency,and potentially terabit/sec operation in the near infrared. Comparisons are made with the fiber optic switching approach. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48.
We will describe research being conducted in the following areas: high-speed, 50 ohm, phased-matched modulators and their applications to digital links; promising new research on flat-panel displays that will be full color, fast response, very thin, and have a very high resolution; all optical switches that are extremely fast, integrable and do not have the latency problems that exist with current optical switches; semiconductor optical amplifiers that are monolithically integrable, more flexible and less expensive than existing fiber amplifiers; novel, semiconductor waveguide devices; and automated packaging techniques that will lower the cost of photonics components.
A laser-based two-pulse correlation technique is used to investigate the mechanisms of photon absorption and the decay of surface excitation on Al<SUB>2</SUB>O<SUB>3</SUB>(1120). The mechanism for emission of positive or neutral particles depends on the wavelength and/or pulsewidth. In our previous study for a pulsewidth of 80 picoseconds at 1064 nm the lifetime of the surface excitation leading to detectable emission and further to optical surface damage was measured to be approximately 200 picoseconds. However, for 800 femtosecond pulses at 616 nm the measured lifetime is a few nanoseconds. In both cases a low-order absorption process is indicated.
Optical damage mechanisms for submicron thick, electron beam deposited HfO<SUB>2</SUB> and SiO<SUB>2</SUB> films on BK-7 substrates have been investigated by monitoring the emission of neutral constituents during excitation with time-delayed pairs of 70 ps laser pulses at a wavelength of 1064 nm. In silica, and probably also HfO<SUB>2</SUB>, linear absorption is the mechanism for energy deposition into the films by the laser beams. Sporadic ablation observed for the HfO<SUB>2</SUB> films may be related to optical conditioning of multilayer HfO<SUB>2</SUB>-SiO<SUB>2</SUB> high-reflector coatings.