L. Pavesi

POROUS SILICON: A QUANTUM SPONGE STRUCTURE FOR SILICON BASED OPTOELECTRONICS

Abstract The striking photoluminescence properties of porous silicon have attracted considerable research interest since their discovery in 1990. Luminescence is due to excitonic recombination quantum confined in Si nanocrystals which remain after the partial electrochemical dissolution of silicon. Porous silicon is constituted by a nanocrystalline skeleton (quantum sponge) immersed in a network of pores. As a result, porous silicon is characterized by a very large internal surface area (of the order of 500 m 2 / cm 3 ). This internal surface is passivated but remains highly chemically reactive which is one of the essential features of this new and complex material. We present an overview of the experimental characterization and theoretical modeling of porous silicon, from the preparation up to various applications. Emphasis is devoted to the optical properties of porous silicon which are closely related to the quantum nature of the Si nanostructures. The characteristics of the various luminescence bands are analyzed and the underlying basic mechanisms are presented. In the quest of an efficient electroluminescent device, we survey the results for several porous silicon contacts, with particular attention to the interface properties, to the stability requirement and to the carrier injection mechanisms. Other device applications are discussed as well.

Photoluminescence of AlxGa1−xAs alloys

A thorough discussion of the various features of the photoluminescence spectra of undoped, p‐doped and n‐doped AlxGa1−xAs (0≤x≤1) alloys is given. This review covers spectral features in the energy region ranging from the energy band gap down to ≂0.8 eV, doping densities from isolated impurities to strongly interacting impurities (heavy‐doping effects) and lattice temperatures from 2 to 300 K. The relevance of photoluminescence as a simple but very powerful characterization technique is stressed also in comparison with other experimental methods. The most recent determinations of the Al concentration dependence of some physical properties of the alloy (energy gaps, carrier effective masses, dielectric constants, phonon energies, donor and acceptor binding energies, etc.) are given. The main physical mechanisms of the radiative recombination process in semiconductors are summarized with particular emphasis on the experimental data available for AlxGa1−xAs. The effects of the nature of the band gap (direct ...

Light emitting silicon for microphotonics

Introduction: Fundamental Aspects.- Electron States and Optical Properties in Confined Silicon Structures.- Porous Silicon.- Silicon Nanostructures: Wells, Wires, and Dots.- Light Emission of Er3+ in Silicon.- Silicon Based Photonic Crystals.- Conclusions and Future Outlook.

Will silicon be the photonic material of the third millenium

Silicon microphotonics, a technology which merges photonics and silicon microelectronic components, is rapidly evolving. Many different fields of application are emerging: transceiver modules for optical communication systems, optical bus systems for ULSI circuits, I/O stages for SOC, displays, .... In this review I will give a brief motivation for silicon microphotonics and try to give the state-of-the-art of this technology. The ingredient still lacking is the silicon laser: a review of the various approaches will be presented. Finally, I will try to draw some conclusions where silicon is predicted to be the material to achieve a full integration of electronic and optical devices.

Porous silicon microcavities as optical chemical sensors

The optical properties of porous silicon microcavities are strongly dependent on the environment. For highly luminescent samples, both the luminescence intensity and the peak position are affected by organic substances, giving the possibility to obtain dual-parameter optical sensors. While the peak position depends on the organic compound refractive index, luminescence intensity depends on its low-frequency dielectric constant. This allows the discrimination between different organic substances. This sensor is particularly interesting for solvents with low dielectric constant, where the response of electrical sensors is very weak.

Towards the first silicon laser

Preface. Photograph of Participants. Introduction. Part I: Light emitting diodes. High efficiency silicon light emitting diodes M.A. Green, et al. Dislocation-based silicon light emitting devices M.A. Lourenco, et al. Efficient electroluminescence in alloyed silicon diodes O.B. Gusev, et al. Light emitting devices based on silicon nanocrystals A. Irrera, et al. Optical and electrical characteristics of LEDs fabricated from Si-nanocrystals embedded in SiO2 B. Garrido, et al. Electroluminescence in Si/SiO2 Layers L. Heikkilo, et al. Reverse biased porous silicon light emitting diodes S. Lazarouk. Strong blue light emission from ion implanted Si/SiO2 structures W. Skorupa, et al. Si/Ge nanostructures for LED G.E. Cirlin, et al. Part II: Silicon nanocrystals. Optical spectroscopy of single silicon quantum dots J. Valenta, et al. Luminescence from Si/SiO2 nanostructures Y. Kanemitsu. Electronic and dielectric properties of porous silicon D. Kovalev, J. Diener. Silicon technology used for size-controlled silicon nanocrystals M. Zacharias, et al. Structural and optical properties of silicon nanocrystals embedded in Silicon Oxide films M. Miu, et al. Part III: Optical gain in silicon nanocrystals. Stimulated emission in silicon nanocrystals L. Dal Negro, et al. Lasing effects in ultrasmall silicon nanoparticles M.H. Nayfeh. On fast optical gain in silicon nanostructures L. Khriachtchev, M. Rasanen. Experimental observation of optical amplification in silicon nanocrystals M. Ivanda, et al. Optical amplification in nanocrystalline silicon superlattices P.M. Fauchet, Jinhao Ruan.Optical gain from silicon nanocrystals: a critical perspective A. Polman, R.G. Elliman. Optical gain measurements with variable stripe length technique J. Valenta, et al. Part IV: Theory of silicon nanocrystals. Theory of silicon nanocrystals C. Delerue, et al. Gain theory and models in silicon nanostructures S. Ossicini, et al. Part V: Silicon/Germanium quantum dots and quantum cascade structures. Si-Ge quantum dot laser: What can we learn from III-V experience? N.N. Ledentsov. Promising SiGe superlattice and quantum well laser candidates G. Sun, et al. Optical properties of arrays of Ge/Si quantum dots in electric field A.V. Dvurechenskii, A.I. Yakimov. MBE of Si-Ge heterostructures with Ge nanocrystals P.P. Pchelyakov, et al. Strain compensated Si/SiGe quantum cascade emitters grown on SiGe pseudosubstrates L. Diehl, et al. Part VI: Terahertz silicon laser. Terahertz silicon laser: Intracenter optical pumping S.G. Pavlov, et al. Silicon lasers based on shallow donor centers: Theoretical background and experimental results V.N. Shastin, et al. Resonant states in modulation doped SiGe Heterostructures as a source of THz lasing A.A. Prokofiev, et al. THz lasing of strained p-Ge and Si/Ge structures M.S. Kagan. Terahertz emission from Silicon-Germanium quantum cascade R.W Kelsall, et al. Part VII: Optical gain in Er doped Si nanocrystals. Towards an Er-doped Si nanocrystal sensitized waveguide laser: The thin line between gain and loss P.G. Kik, A. Polman. Optical gain using nanocrystal sensitized Erbium Jung H. Shin, et al. Excitation mechanism of Er photoluminescence in bulk Si and SiO2 with nanocryst

Second-harmonic generation in silicon waveguides strained by silicon nitride

Silicon photonics meets the electronics requirement of increased speed and bandwidth with on-chip optical networks. All-optical data management requires nonlinear silicon photonics. In silicon only third-order optical nonlinearities are present owing to its crystalline inversion symmetry. Introducing a second-order nonlinearity into silicon photonics by proper material engineering would be highly desirable. It would enable devices for wideband wavelength conversion operating at relatively low optical powers. Here we show that a sizeable second-order nonlinearity at optical wavelengths is induced in a silicon waveguide by using a stressing silicon nitride overlayer. We carried out second-harmonic-generation experiments and first-principle calculations, which both yield large values of strain-induced bulk second-order nonlinear susceptibility, up to 40 pm V(-1) at 2,300 nm. We envisage that nonlinear strained silicon could provide a competing platform for a new class of integrated light sources spanning the near- to mid-infrared spectrum from 1.2 to 10 μm.

APPLICATION TO OPTICAL COMPONENTS OF DIELECTRIC POROUS SILICON MULTILAYERS

Narrow‐band color filters have been integrated on porous silicon layers. Distributed Bragg reflectors and Fabry–Perot interference filters based on layered porous silicon samples are demonstrated. The effects of narrowing and tuning the porous silicon emission band are shown in structures composed by Fabry–Perot filters integrated on top of thick porous silicon layers.

Ultrafast All-Optical Switching in a Silicon-Nanocrystal-Based Silicon Slot Waveguide at Telecom Wavelengths

We demonstrate experimentally all-optical switching on a silicon chip at telecom wavelengths. The switching device comprises a compact ring resonator formed by horizontal silicon slot waveguides filled with highly nonlinear silicon nanocrystals in silica. When pumping at power levels about 100 mW using 10 ps pulses, more than 50% modulation depth is observed at the switch output. The switch performs about 1 order of magnitude faster than previous approaches on silicon and is fully fabricated using complementary metal oxide semiconductor technologies.

Size dependence of lifetime and absorption cross section of Si nanocrystals embedded in SiO2

Photoluminescence lifetimes and optical absorption cross sections of Si nanocrystals embedded in SiO 2 have been studied as a function of their average size and emission energy. The lifetimes span from 20 μs for the smallest sizes (2.5 nm) to more than 200 μs for the largest ones (7 nm). The passivation of nonradiative interface states by hydrogenation increases the lifetime for a given size. In contrast with porous Si, the cross section per nanocrystal shows a nonmonotonic behavior with emission energy. In fact, although the density of states above the gap increases for larger nanocrystals, this trend is compensated by a stronger reduction of the oscillator strength, providing an overall reduction of the absorption cross section per nanocrystal for increasing size.