There is an urgent requirement for an optical emitter that is compatible with standard, silicon-based ultra-large-scale integration (ULSI) technology. Bulk silicon has an indirect energy bandgap and ...is therefore highly inefficient as a light source, necessitating the use of other materials for the optical emitters. However, the introduction of these materials is usually incompatible with the strict processing requirements of existing ULSI technologies. Moreover, as the length scale of the devices decreases, electrons will spend increasingly more of their time in the connections between components; this interconnectivity problem could restrict further increases in computer chip processing power and speed in as little as five years. Many efforts have therefore been directed, with varying degrees of success, to engineering silicon-based materials that are efficient light emitters. Here, we describe the fabrication, using standard silicon processing techniques, of a silicon light-emitting diode (LED) that operates efficiently at room temperature. Boron is implanted into silicon both as a dopant to form a p-n junction, as well as a means of introducing dislocation loops. The dislocation loops introduce a local strain field, which modifies the band structure and provides spatial confinement of the charge carriers. It is this spatial confinement which allows room-temperature electroluminescence at the band-edge. This device strategy is highly compatible with ULSI technology, as boron ion implantation is already used as a standard method for the fabrication of silicon devices.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Although silicon has long been the material of choice for most microelectronic applications, it is a poor emitter of light (a consequence of having an 'indirect' bandgap), so hampering the ...development of integrated silicon optoelectronic devices. This problem has motivated numerous attempts to develop silicon-based structures with good light-emission characteristics, particularly at wavelengths (∼1.5 μm) relevant to optical fibre communication. For example, silicon-germanium superlattice structures can result in a material with a pseudo-direct bandgap that emits at ∼1.5 μm, and doping silicon with erbium introduces an internal optical transition having a similar emission wavelength, although neither approach has led to practical devices. In this context, β-iron disilicide has attracted recent interest as an optically active, direct-bandgap material th might be compatible with existing silicon processing technology. Here we report the realization of a light-emitting device operating at 1.5 μm that incorporates β-FeSi2 into a conventional silicon bipolar junction. We argue that this result demonstrates the potential of β-FeSi2 as an important candidate for a silicon-based optoelectronic technology.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We report on the super enhancement of the 1.54 μm Er emission in erbium doped silicon-on-insulator when codoped with oxygen at a ratio of 1:1. This is attributed to a more favourable crystal field ...splitting in the substitutional tetrahedral site favoured for the singly coordinated case. The results on these carefully matched implant profiles show that optical response is highly determined by the amount and ratio of erbium and oxygen present in the sample and ratios of O:Er greater than unity are severely detrimental to the Er emission. The most efficient luminescence is forty times higher than in silicon-on-insulator implanted with Er only. This super enhancement now offers a realistic route not only for optical communication applications but also for the implementation of silicon photonic integrated circuits for sensing, biomedical instrumentation and quantum communication.
The effects of helium ion irradiation on immiscible AlN/TiN multilayered system were studied. The structure consisted of 30 alternate AlN (~8nm) and TiN (~9.3nm) layers of a total thickness around ...260nm, deposited on (100) Si substrates by reactive sputtering. The system was then implanted with 30keV He+ to very high irradiation doses, 1–4×1017ions/cm2. Evaluated projected ion range was 153.1±45.4nm and maximum displacements per atom for the applied doses from 6 to 24. It was found that the multilayers remained well separated and stable after irradiation to 1×1017ions/cm2, which introduces up to 10at.% of He within the structure. The main effects were agglomeration of He bubbles around the projected ion range, mostly concentrated at the AlN edges of the interfaces, and a slight increase of the mean grain size within the affected zone. Increasing of the ion dose induced further agglomeration of bubbles, splitting of the layers at the interfaces, and final destruction of the structure. The evaluated He content was consistent with the implanted dose up to 2×1017ions/cm2. For the highest dose the implanted gas is partially released from the structure. The results can be interesting towards the development of radiation tolerant materials.
•AlN/TiN multilayered system was implanted with 30keV He+ up to 4×1017ions/cm2.•Multilayered structure is radiation tolerant up to a dose of 1×1017ions/cm2.•Helium agglomerates in form of bubbles at AlN edge of the interfaces.•The highest dose induces delamination of multilayered structure.
Declines in habitat and wildlife in semiarid African savannas are widely reported and commonly attributed to agropastoral population growth, livestock impacts, and subsistence cultivation. However, ...extreme annual and shorter-term variability of rainfall, primary production, vegetation, and populations of grazers make directional trends and causal chains hard to establish in these ecosystems. Here two decades of changes in land cover and wildebeest in the Serengeti-Mara region of East Africa are analyzed in terms of potential drivers (rainfall, human and livestock population growth, socio-economic trends, land tenure, agricultural policies, and markets). The natural experiment research design controls for confounding variables, and our conceptual model and statistical approach integrate natural and social sciences data. The Kenyan part of the ecosystem shows rapid land-cover change and drastic decline for a wide range of wildlife species, but these changes are absent on the Tanzanian side. Temporal climate trends, human population density and growth rates, uptake of small-holder agriculture, and livestock population trends do not differ between the Kenyan and Tanzanian parts of the ecosystem and cannot account for observed changes. Differences in private versus state/communal land tenure, agricultural policy, and market conditions suggest, and spatial correlations confirm, that the major changes in land cover and dominant grazer species numbers are driven primarily by private landowners responding to market opportunities for mechanized agriculture, less by agropastoral population growth, cattle numbers, or small-holder land use.
We review progress in silicon LEDs using dislocation engineering to achieve high temperature operation, a process that is fully CMOS (Complementary Metal Oxide Semiconductor) compatible. We ...concentrate on devices operating in the near infra-red where high value applications are. The need for silicon emitters, lasers and optical amplifiers is discussed followed by an outline of previous approaches and possible future routes explored. Results on gain in silicon are reported and routes to electrically pumped injection lasers and optical amplifiers considered. Extension of 1.1 and 1.5
μm devices to other wavelengths is discussed.
Within the field of environmental management and conservation, the concept of well-being is starting to gain traction in monitoring the socio-economic and cultural impact of interventions on local ...people. Here we consider the practical trade-offs policy makers and practitioners must navigate when utilizing the concept of well-being in environmental interventions. We first review current concepts of well-being before considering the need to balance the complexity and practical applicability of the definition used and to consider both positive and negative components of well-being. A key determinant of how well-being is operationalized is the identity of the organization wishing to monitor it. We describe the trade-offs around the external and internal validity of different approaches to measuring well-being and the relative contributions of qualitative and quantitative information to understanding well-being. We explore how these trade-offs may be decided as a result of a power struggle between stakeholders. Well-being is a complex, multi-dimensional, dynamic concept that cannot be easily defined and measured. Local perspectives are often missed during the project design process as a result of the more powerful voices of national governments and international NGOs, so for equity and local relevance it is important to ensure these perspectives are represented at a high level in project design and implementation.
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