Nanocavity shrinkage and preferential amorphization during irradiation in silicon

We model the recent experimental results and demonstrate that the internal shrinkage of nanocavities in silicon is intrinsically associated with preferential amorphization as induced by self-ion irradiation. The results reveal novel thermodynamic nonequilibrium properties of such an open-volume nanostructure in condensed matter and also of covalently bound amorphous materials both at nanosize scale and during ultrafast interaction with energetic beam.

A new technique for boosting efficiency of silicon solar cells

A new type of photovoltaic system with higher generation power density has been studied in detail. The feature of the system is a V-shaped module (VSM) with two tilted monocrystalline solar cells. Compared to solar cells in a flat orientation, the VSM enhances external quantum efficiency and leads to an increase of 31% in power conversion efficiency. Due to the VSM technique, short-circuit current density was raised from 24.94 to 33.7mA/cm(2), but both fill factor and open-circuit voltage were approximately unchanged. For the VSM similar results (about 30% increase) were obtained for solar cells fabricated by using mono-crystal line silicon wafers with only conventional background impurities. (c) 2004 Elsevier B.V. All rights reserved.

Research on improved methods of reduction of bend loss of silicon-on-insulator waveguides

Improved methods of reduction of bend loss of silicon-on-insulator waveguides were simulated and analyzed by means of effective index method (EIM) and two dimensional beam propagation method (2D-BPM). The simulation results indicate that two different methods, one of which are introducing an offset at the junction of two waveguides and the other is etching groove at the outside of bend waveguide, can decrease bend loss. And the later one is more effective. Meanwhile, experiments validate them. By etching groove, the insertion loss of bend waveguide of R = 16mm, transverse displacement 70mum was decreased 5dB. And its bend loss was almost eliminated.

Thermally tunable optical filter with crystalline silicon as cavity

A novel method to fabricate a thermally tunable filter with a tuning range of 26 nm from 1.504 to 1.530 mum is reported. The high-reffectivity bottom mirror is deposited in the hole formed by anisotropically etching in the basic solution from the backside of the slice with the buried SiO2 layer in silicon-on-insulator substrate as the etching-stop layer. Because of the formation of the mesa and the removing of the substrate of the hole, the power from the metal heater can be more effectively consumed in the crystalline silicon cavity. So it lowers the power consumption and the filter has a higher tuning range. (C) 2004 Elsevier B.V. All rights reserved.

Technique for enhancing generation power density of silicon photovoltaic devices

A new type of photovoltaic system with higher generation power density has been studied in detail. The feature of the proposed system is a V-shaped structure with two polycrystalline solar cells. Compared to solar cells in a conventional approach, the V-shaped structure enhances external quantum efficiency and leads to an increase of 24% in power conversion efficiency.

Silicon-on-insulator based electro-optic variable optical attenuator with a series structure

An electro-optic variable optical attenuator in silicon-on-insulator is designed and fabricated. A series Structure is used to improve the device efficiency Compared to the attenuator in the single p-i-n diode Structure in the same modulating length, the attenuation range of the device in the series structure improves 2-3 times in the same injecting current density, while the insertion loss is not affected. The maximum dynamic attenuation of the device is greater than 30 dB. The response frequency is obtained to be about 2 MHz.

Silicon-on-insulator-based waveguide switch with fast response

Based on thermo-optical effect of silicon, a 2 x 2 switch is fabricated in silicon-on-insulator by chemical etching. The switch presents an extinction ratio of 26 dB and a power consumption of 169 mW. The response time F similar to 10.5 mus.

Novel folding large-scale optical switch matrix with total internal reflection mirrors on silicon-on-insulator by anisotropy chemical etching

A compact optical switch matrix was designed, in which light circuits were folded by total internal reflective (TIR) mirrors. Two key elements, 2 x 2 switch and TIR mirror, have been fabricated on silicon-on-insulator wafer by anisotropy chemical etching. The 2 x 2 switch showed very low power consumption of 140 mW and a very high speed of 8 +/- 1 mus. An improved design for the TIR mirror was developed, and the fabricated mirror with smooth and vertical reflective facet showed low excess loss of 0.7 +/- 0.3 dB at 1.55 mum.

Boron-doped silicon nanowires grown by plasma-enhanced chemical vapor deposition

Boron-doped ( B-doped) silicon nanowires have been successfully synthesized by plasma-enhanced chemical vapor deposition (PECVD) at 440degreesC using silane as the Si source, diborane( B2H6) as the dopant gas and An as the catalyst. It is desirable to extend this technique to the growth of silicon nanowire pn junctions because PECVD enables immense chemical reactivity.

Stress reduction in GaN films on (111) silicon-on-insulator substrate grown by metal-organic chemical vapor deposition

The GaN film was grown on the (111) silicon-on-insulator (SOI) substrate by metal-organic chemical vapor deposition and then annealed in the deposition chamber. A multiple beam optical stress sensor was used for the in-situ stress measurement, and X-ray diffraction (XRD) and Raman spectroscopy were used for the characterization of GaN film. Comparing the characterization results of the GaN films on the bulk silicon and SOI substrates, we can see that the Raman spectra show the 3.0 cm(-1) frequency shift of E-2(TO), and the full width at half maximum of XRD rocking curves for GaN (0002) decrease from 954 arc see to 472 are sec. The results show that the SOI substrates can reduce the tensile stress in the GaN film and improve the crystalline quality. The annealing process is helpful for the stress reduction of the GaN film. The SOI substrate with the thin top silicon film is more effective than the thick top silicon film SOI substrate for the stress reduction. (C) 2007 Elsevier B.V. All rights reserved.

Stress evolution influenced by oxide charges on GaN metal-organic chemical vapor deposition on silicon-on-insulator substrate

GaN epilayers have been deposited on silicon-on-insulator (SOI) and bulk silicon substrates. The stress transition thickness and the initial compressive stress of a GaN epilayer on the SOI substrate are larger than those on the bulk silicon substrate, as shown in in situ stress measurement results. It is mainly due to the difference of the three-dimensional island density and the threading dislocation density in the GaN layer. It can increase the compressive stress in the initial stage of growth of the GaN layer, and helps to offset the tensile stress generated by the lattice mismatch.

A photonic crystal waveguide with silicon on insulator in the near-infrared band

A two-dimensional (2D) photonic crystal waveguide in the Gamma-K direction with triangular lattice on a silicon-on insulator (SOI) substrate in the near-infrared band is fabricated by the combination of electron beam lithography and inductively coupled plasma etching. Its transmission characteristics are analysed from the stimulated band diagram by the effective index and the 2D plane wave expansion (PWE) methods. In the experiment, the transmission band edge in a longer wavelength of the photonic crystal waveguide is about 1590 nm, which is in good qualitative agreement with the simulated value. However, there is a disagreement between the experimental and the simulated results when the wavelength ranges from 1607 to 1630 nm, which can be considered as due to the unpolarized source used in the transmission measurement.

A novel implantable multichannel silicon-based microelectrode

Silicon-based microelectrodes have been confirmed to be helpful in neural prostheses. The fabricated 7-channel silicon-based microelectrode was feasible to be implanted into the brain cortex. The manufacturing process by microelectromechanical system (MEMS) technology was detailed with four photolithographic masks. The microscopic photographs and SEM images indicated that the probe shank was 3mm long, 100 mu m wide and 20 mu m thick with the recording sites spaced 120 mu m apart for good signal isolation. To facilitate the insertion and minimize the trauma, the microelectrode is narrowed down gradually near the tip with the tip taper angle of 6 degrees. Curve of the single recording site impedance versus frequency was shown by test in vitro and the impedance declined from 150.5 k Omega to 6.0 k Omega with frequency changing from 10 k to 10MHz.

Directional-coupler-based Mach-Zehnder interferometer in silicon-on-insulator technology for optical intensity modulation

Based on silicon-on-insulator (SOI) technology, a Mach-Zehnder interferometer (MZI) is fabricated, in which two directional couplers serve as power splitter and combiner. The free carrier plasma dispersion effect of Si is adopted to achieve the phase modulation and the consequent intensity modulation of optical fields. The device presents an insertion loss of 2.61 dB and an extinction ratio of 19.6 dB. The rise time and fall time are 676 ns and 552 ns, respectively. Detailed analysis and explanation of the performance behaviors are also presented. (c) 2007 Society of Photo-Optical Instrumentation Engineers.

Submicrosecond rearrangeable nonblocking silicon-on-insulator thermo-optic 4 X 4 switch matrix

A rearrangeable nonblocking silicon-on-insulator-based thermo-optic 4 X 4 switch matrix is designed and fabricated. A spot-size converter is integrated to reduce the insertion loss, and a new driving circuit is designed to improve the response speed. The insertion loss is less than 10 dB, and the response time is 950 us. (c) 2007 Optical Society of America