Silicon mirror suspensions for gravitational wave detectors

One of the most significant limits to the sensitivity of current, and future, long-baseline interferometric gravitational wave detectors is thermal displacement noise of the test masses and their suspensions. This paper reports results of analytical and experimental studies of the limits to thermal noise performance of cryogenic silicon test mass suspensions set by two constraints on suspension fibre dimensions: the minimum dimensions required to allow conductive cooling for extracting incident laser beam heat deposited in the mirrors; and the minimum dimensions of fibres (set by their tensile strength) which can support test masses of the size envisaged for use in future detectors. We report experimental studies of breaking strength of silicon ribbons, and resulting design implications for the feasibility of suspension designs for future gravitational wave detectors using silicon suspension fibres. We analyse the implication of this study for thermal noise performance of cryogenically cooled silicon suspensions

Process Research On Polycrystalline Silicon Material (PROPSM)

Performance limiting mechanisms in polycrystalline silicon are investigated by fabricating a matrix of solar cells of various thicknesses from polycrystalline silicon wafers of several bulk resistivities. The analysis of the results for the entire matrix indicates that bulk recombination is the dominant factor limiting the short circuit current in large grain (greater than 1 to 2 mm diameter) polycrystalline silicon, the same mechanism that limits the short circuit current in single crystal silicon. An experiment to investigate the limiting mechanisms of open circuit voltage and fill factor for large grain polycrystalline silicon is designed. Two process sequences to fabricate small cells are investigated

Raman study of Fano interference in p-type doped silicon

As the silicon industry continues to push the limits of device dimensions, tools such as Raman spectroscopy are ideal to analyze and characterize the doped silicon channels. The effect of inter-valence band transitions on the zone center optical phonon in heavily p-type doped silicon is studied by Raman spectroscopy for a wide range of excitation wavelengths extending from the red (632.8 nm) into the ultra-violet (325 nm). The asymmetry in the one-phonon Raman lineshape is attributed to a Fano interference involving the overlap of a continuum of electronic excitations with a discrete phonon state. We identify a transition above and below the one-dimensional critical point (E = 3.4 eV) in the electronic excitation spectrum of silicon. The relationship between the anisotropic silicon band structure and the penetration depth is discussed in the context of possible device applications.Comment: 6 pages, 7 figures, pape

Nonlinear optical interactions in silicon waveguides

The strong nonlinear response of silicon photonic nanowire waveguides allows for the integration of nonlinear optical functions on a chip. However, the detrimental nonlinear optical absorption in silicon at telecom wavelengths limits the efficiency of many such experiments. In this review, several approaches are proposed and demonstrated to overcome this fundamental issue. By using the proposed methods, we demonstrate amongst others supercontinuum generation, frequency comb generation, a parametric optical amplifier, and a parametric optical oscillator

mm-Wave Silicon ICs: Challenges and Opportunities

Millimeter-waves offer promising opportunities and interesting challenges to silicon integrated circuit and system designers. These challenges go beyond standard circuit design questions and span a broader range of topics including wave propagation, antenna design, and communication channel capacity limits. It is only meaningful to evaluate the benefits and shortcoming of silicon-based mm-wave integrated circuits in this broader context. This paper reviews some of these issues and presents several solutions to them

State-of-the-art all-silicon sub-bandgap photodetectors at telecom and datacom wavelengths

Silicon-based technologies provide an ideal platform for the monolithic integration of photonics and microelectronics. In this context, a variety of passive and active silicon photonic devices have been developed to operate at telecom and datacom wavelengths, at which silicon has minimal optical absorption - due to its bandgap of 1.12 eV. Although in principle this transparency window limits the use of silicon for optical detection at wavelengths above 1.1 μm, in recent years tremendous advances have been made in the field of all-silicon sub-bandgap photodetectors at telecom and datacom wavelengths. By taking advantage of emerging materials and novel structures, these devices are becoming competitive with the more well-established technologies, and are opening new and intriguing perspectives. In this paper, a review of the state-of-the-art is presented. Devices based on defect-mediated absorption, two-photon absorption and the internal photoemission effect are reported, their working principles are elucidated and their performance discussed and compared

Ga^+ beam lithography for nanoscale silicon reactive ion etching

By using a dry etch chemistry which relies on the highly preferential etching of silicon, over that of gallium (Ga), we show resist-free fabrication of precision, high aspect ratio nanostructures and microstructures in silicon using a focused ion beam (FIB) and an inductively coupled plasma reactive ion etcher (ICP-RIE). Silicon etch masks are patterned via Ga^+ ion implantation in a FIB and then anisotropically etched in an ICP-RIE using fluorinated etch chemistries. We determine the critical areal density of the implanted Ga layer in silicon required to achieve a desired etch depth for both a Pseudo Bosch (SF_6/C_4F_8) and cryogenic fluorine (SF_6/O_2) silicon etching. High fidelity nanoscale structures down to 30 nm and high aspect ratio structures of 17:1 are demonstrated. Since etch masks may be patterned on uneven surfaces, we utilize this lithography to create multilayer structures in silicon. The linear selectivity versus implanted Ga density enables grayscale lithography. Limits on the ultimate resolution and selectivity of Ga lithography are also discussed