Erbium doped materials are of great interest in thin film integrated optoelectronic technology, due to their Er3+ intra-4f emission at 1.54 μm, a standard telecommunication wavelength. Er-doped dielectric thin films can be used to fabricate planar optical amplifiers or lasers that can be integrated with other devices on the same chip. Semiconductors, such as silicon, can also be doped with erbium. In this case the Er may be excited through optically or electrically generated charge carriers. Er-doped Si light-emitting diodes may find applications in Si-based optoelectronic circuits. In this article, the synthesis, characterization, and application of several different Er-doped thin film photonic materials is described. It focuses on oxide glasses (pure SiO2, phosphosilicate, borosilicate, and soda-lime glasses), ceramic thin films (Al2O3, Y2O3, LiNbO3), and amorphous and crystalline silicon, all doped with Er by ion implantation. MeV ion implantation is a technique that is ideally suited to dope these materials with Er as the ion range corresponds to the typical micron dimensions of these optical materials. The role of implantation defects, the effect of annealing, concentration dependent effects, and optical activation are discussed and compared for the various materials.

Erbium implanted thin film photonic materials

Monolithic lasers on Si are ideal for high-volume and large-scale electronic-photonic integration. Ge is an interesting candidate owing to its pseudodirect gap properties and compatibility with Si complementary metal oxide semiconductor technology. Recently we have demonstrated room-temperature photoluminescence, electroluminescence, and optical gain from the direct gap transition of band-engineered Ge-on-Si using tensile strain and n-type doping. Here we report what we believe to be the first experimental observation of lasing from the direct gap transition of Ge-on-Si at room temperature using an edge-emitting waveguide device. The emission exhibited a gain spectrum of 1590-1610 nm, line narrowing and polarization evolution from a mixed TE/TM to predominantly TE with increasing gain, and a clear threshold behavior.

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Ge-on-Si laser operating at room temperature.

Recent developments in rare-earth doped materials for optoelectronics

Silicon has long been established as the material of choice for the microelectronics industry. This is not yet true in photonics, where the limited degrees of freedom in material design combined with the indirect bandgap are a major constraint. Recent developments, especially those enabled by nanoscale engineering of the electronic and photonic properties, are starting to change the picture, and some silicon nanostructures now approach or even exceed the performance of equivalent direct-bandgap materials. Focusing on two application areas, namely communications and photovoltaics, we review recent progress in silicon nanocrystals, nanowires and photonic crystals as key examples of functional nanostructures. We assess the state of the art in each field and highlight the challenges that need to be overcome to make silicon a truly high-performing photonic material.

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Silicon nanostructures for photonics and photovoltaics

Size dependence of nanostructures: Impact of bond order deficiency

We have carried out a study of the photoluminescence properties of silicon‐rich silica. A series of films grown using plasma enhanced chemical vapor deposition over a range of growth conditions were annealed under argon at selected temperatures. Photoluminescence spectra were measured for each film at room temperature and for selected films at cryogenic temperatures. The photoluminescence spectra exhibit two bands. Fourier transform infrared and electron spin resonance spectroscopies were used to investigate bonding and defect states within the films. The data obtained strongly suggest the presence of two luminescence mechanisms which exhibit different dependencies on film growth conditions and postprocessing. We make assignments of the two mechanisms as (1) defect luminescence associated with oxygen vacancies and (2) radiative recombination of electron‐hole pairs confined within nanometer‐size silicon clusters (‘‘quantum confinement’’).

The origin of photoluminescence from thin films of silicon-rich silica

We report the fabrication by PECVD of silicon-rich erbium-doped silica films that exhibit both 1535 nm fluorescence and visible photoluminescence. Fluorescence spectra are presented along with absorption spectra that display a strong band edge in the blue, which we ascribe to the presence of Si microclusters. We are unable to observe characteristic Er3+ absorption bands and propose that excitation of the rare earth is via an energy transfer process from Si microclusters.

Optical-properties of pecvd erbium-doped silicon-rich silica - evidence for energy-transfer between silicon microclusters and erbium ions (vol 6, pg l 319, 1994)

http://iopscience.iop.org/article/10.1088/0953-8984/6/21/007/pdf

Optical-properties of pecvd erbium-doped silicon-rich silica - evidence for energy-transfer between silicon microclusters and erbium ions

We present a model for the luminescence spectrum of silicon nanoclusters. We propose that the major contribution to luminescence is from radiative recombination of confined excitons (quantum confinement). Utilizing the effective mass approximation we consider the variation in oscillator strength with cluster size and the associated change in the number of available free carriers. By varying both the mean cluster size and size distribution of silicon nanoclusters, the luminescence spectra are modeled to a good fit. We compare our model with experimental photoluminescence and electroluminescence data from this group and from others.

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Modeling the contribution of quantum confinement to luminescence from silicon nanoclusters

A computer modelling method for the three-dimensional dynamic analysis of liquid crystal display cells is presented. The method is based on a variational approach to the Oseen-Frank free energy formulation considering three elastic constants and uses a vectorial representation of the director field. A simpler approximate form that uses only two elastic constants but is faster to operate is obtained as a by-product of the full three-constant model implementation. The modelling uses finite elements on a mesh of tetrahedral elements for the calculation of directors and electric potentials while finite differences in time are used in the time stepping process. Comparisons are made with results from a 2D dynamic program using a tensor model giving good agreement.

P.F. Trwoga

Papers

The origin of photoluminescence from thin films of silicon-rich silica

Optical-properties of pecvd erbium-doped silicon-rich silica - evidence for energy-transfer between silicon microclusters and erbium ions (vol 6, pg l 319, 1994)

Optical-properties of pecvd erbium-doped silicon-rich silica - evidence for energy-transfer between silicon microclusters and erbium ions

Modeling the contribution of quantum confinement to luminescence from silicon nanoclusters

Three-dimensional modelling of liquid crystal display cells using finite elements