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

Erbium-doped fiber devices have been extraordinarily successful due to their broad optical gain around 1.5–1.6 μm. Er-doped fiber amplifiers enable efficient, stable amplification of high-speed, wavelength-division-multiplexed signals, thus continue to dominate as part of the backbone of longhaul telecommunications networks. At the same time, Er-doped fiber lasers see many applications in telecommunications as well as in biomedical and sensing environments. Over the last 20 years significant efforts have been made to bring these advantages to the chip level. Device integration decreases the overall size and cost and potentially allows for the combination of many functions on a single tiny chip. Besides technological issues connected to the shorter device lengths and correspondingly higher Er concentrations required for high gain, the choice of appropriate host material as well as many design issues come into play in such devices. In this contribution the important developments in the field of Er-doped integrated waveguide amplifiers and lasers are reviewed and current and future potential applications are explored. The vision of integrating such Er-doped gain devices with other, passive materials platforms, such as silicon photonics, is discussed.

Erbium-doped integrated waveguide amplifiers and lasers

We demonstrate coherent control of spontaneous emission from a three-level atom with one resonant frequency near the edge of a photonic band gap. As a result of quantum interference and photon localization, spontaneous emission can be totally suppressed or strongly enhanced depending on the relative phase between the control and pump laser fields. The fractionalized steady state inversion of the atom depends sensitively on the initial conditions, suggesting the possibility of a phase-sensitive, optical memory device on the atomic scale.

https://www.prl.res.in/~library/Agarwal_GS_5238_97_abst.pdf

Coherent Control of Spontaneous Emission near a Photonic Band Edge: A Single-Atom Optical Memory Device

We describe the microfabrication and band structure of large scale three-dimensional (3D) photonic bandgap (PBG) materials based on self-organizing templates. The simplest of these templates is an fcc lattice of close-packed, weakly sintered spheres. Other templates include hcp and hexagonal AB/sub 2/ self-organizing photonic crystals. These photonic crystals may be converted into PEG materials by partially infiltrating the template with high refractive index semiconductors such as Si, Ge, or GaP and subsequently removing the template. The resulting "inverse opal" structure exhibits both a photonic pseudogap and a complete (3D) PBG in the near visible spectrum, spanning up to 15% of the gap center frequency. The local density of states (LDOS) for photons exhibits considerable variation from point to point in coordinate space and reveals large spectral gaps even in the absence of a PEG in the total density of states. These gaps in the LDOS may lead to novel effects in quantum and nonlinear optics when active atoms or molecules are placed within the PBG material. These effects include anomalous, low threshold nonlinear response, collective atomic switching, and low-threshold all-optical transistor action. When an optically birefringent nematic liquid crystal is infiltrated into the void regions of the "inverse" opal PBG material, the resulting composite material exhibits a completely tunable PBG. In particular, the 3D PBG can be completely opened or closed by applying an electric field which rotates the axis of the nematic molecules relative to the inverse opal backbone.

/pdf/photonic-bandgap-formation-and-tunability-in-certain-self-hprxpebkyq.pdf

Photonic bandgap formation and tunability in certain self-organizing systems

The local structure of an optically active center in erbium-doped zinc oxide (ZnO:Er) thin film produced by a laser ablation technique and its optical activation process are investigated by Er LIII-edge x-ray absorption fine structure analysis using a synchrotron radiation as an x-ray source. In as-ablated ZnO:Er thin film, Er has an approximately five-fold coordination of O surrounded by eight other O atoms as second-nearest neighbors. The high-order coordination of O decreases the Er-related photoluminescence (PL) intensity due to an undesirable crystal field for 4f radiation transition. After annealing in O2 ambient, the local structure of Er changes to a pseudo-octahedral structure with C4v symmetry, similar to the optically activated Er-doped Si (Si:Er), resulting in strong PL. The bond lengths of Er–O are evaluated, and differences in the optical activation processes between ZnO:Er and Si:Er thin films are discussed.

Local structure analysis of an optically active center in Er-doped ZnO thin film

Different Er centres in Si and their use for electroluminescent devices

We report sharp, atomlike electroluminescence spectra close to 1.54 μm from a low-dose (3.5×1018 cm−3) erbium-implanted silicon light-emitting diode operating under forward bias. The well-resolved Stark splitting identifies the isolated interstitial Er with cubic site symmetry as the source. The full width at half maximum of the most intense line is 0.5 nm. A comparison with a highly Er (5×1019 cm−3) and O (1×1020 cm−3) doped diode with a high doping gradient grown by molecular beam epitaxy and with Er-implanted silica is given with respect to fine structure and thermal quenching. The room-temperature emission of the highly Er and O doped diode is ascribed to Er containing silica precipitates within the c-Si matrix.

On the environment of optically active Er in Si-electroluminescence devices

We investigate photoluminescence (PL) and photoluminescence excitation spectroscopy of Er3+ ions implanted into SiO2 films thermally grown on silicon wafers. We show that at 10 K the Er3+ PL excited with the 514.5 nm line of an Ar laser is limited by the total number of Er ions, whereas at resonant excitation within the 960–1000 nm range the PL efficiency is rather concentration limited. Some samples were codoped with Yb3+ ions to study sensitization of the 4f–4f PL of Er3+ ions. At resonant excitation the presence of Yb leads to an enhancement of the Er3+ PL only at dilute Er concentrations.

Excitation of Er3+ ions in silicon dioxide films thermally grown on silicon

We present a high resolution photoluminescence (PL) study of Si:Er which allows to distinguish a variety of Er centers occurring in Er-implanted Si. The lines belonging to a particular center are identified from the influence of processing parameters, temperature, excitation power, co-doping and hydrostatic pressure. The center-dependent high temperature yield is limited by the competition in efficiency of capturing excitons at Er centers or nearby defects followed by the excitation transfer to the Er-4f shell and by recombination of excitons at other, non-radiative centers. The excitation transfer probability is shown to depend on hydrostatic pressure of a few kbar. This effect indicates a new possibility to improve the efficiency of Si:Er light emitters.

S. Lanzerstorfer

Papers

Different Er centres in Si and their use for electroluminescent devices

On the environment of optically active Er in Si-electroluminescence devices

Excitation of Er3+ ions in silicon dioxide films thermally grown on silicon

Factors Governing the Photoluminescence Yield of Erbium Implanted Silicon

Status, Hopes and Limitations for the Si: Er-based 1.54 μm Emitter