Silicone layer

Yet another alternative is the thin-film solar cell. This cannot use silicon, because the transmission of solar radiation through silicon is high enough to require relatively thick silicon layers. One current favourite is the Cu(Ga, InjSci thin-film solar cell, with an efficiency up to 17% in small experimental cells. This material has a very high light absorption and the total thickness of the active layer (on a glass substrate) is only 2 pm. 

Silicon wafer has been extensively used in the semiconductor industry. CMP of silicon is one of the key technologies to obtain a smooth, defect-free, and high reflecting silicon surfaces in microelectronic device patterning. Silicon surface qualities have a direct effect on physical properties, such as breakdown point, interface state, and minority carrier lifetime, etc. Cook et al. [54] considered the chemical processes involved in the polishing of glass and extended it to the polishing of silicon wafer. They presented the chemical process which occurs by the interaction of the silicon layer and the... 

Probe measurements in silane discharges have been reported [296,297]. Apparently, no difficulties were experienced, as the deposited amorphous silicon layer on the tip was sufficiently photoconductive. For typical silane discharge conditions values for are found to be between 2 and 2.5 eV. Electron densities are around 1 x 10 cm - [296]. Probe measurement in the ASTER system failed due to strong distortions of the probe current, even after following cleaning procedures. 

Interferometry on porous silicon The average refractive index of the porous silicon layer is affected by analyte adsorption, resulting in a shift of the Fabry Perot fringes 6,18... 

Illumination of a microporous silicon layer during anodization changes the PL spectrum significantly, as discussed in Section 7.4, and may also be applied for structuring of microporous layers [As2, Dol]. 

To understand the electrochemical behavior of silicon, however, the formation and the properties of anodic oxides are important The formation of an anodic oxide on silicon electrodes in HF and HF-free electrolytes will therefore be discussed in detail in this chapter. The formation of native and chemical oxides is closely related to the electrochemical formation process and will be reviewed briefly. The anodic oxidation of porous silicon layers is closely related to the morphology and the luminescent properties of this material and is therefore discussed in Section 7.6. 

Electropolishing under galvanostatic conditions can be used to remove bulk silicon in a well-defined manner. This can for example be used to profile doping density or diffusion length versus the thickness of the sample, as discussed in Sections 10.2 and 10.3. The thickness D of the removed silicon layer can be calculated from the applied current density J, the anodization time t, the dissolution valence nv, the atomic density of silicon Nsi and the elementary charge e. 

Electropolishing is well established as a simple, in situ method to separate porous silicon layers from the silicon electrode. By switching the anodic current density from values below JPS to a value above JPS, the PS film is separated at its interface to the bulk electrode. The flatness of a PS surface separated by electropolishing is sufficient for optical applications, as shown in Fig. 10.10. 

The cross-section of a macropore may have all shapes between a circle and a four-pointed star, as shown in Fig. 9.12a-e. In addition the pore walls are covered with a microporous silicon layer, as shown in Fig. 9.12h, which makes the determination of AP difficult. In most cases, however, the approximation of the pore cross-section by a square of size d is found to be sufficient. Under this assumption and for a square pattern of pitch i, as shown in Fig. 9.15 a, d becomes simply ... 

NHE OCP ONO OPS PCD PDS PL PLE PMMA PP PP PS PSG PSL PTFE PVC PVDF normal hydrogen electrode (= SHE) open circuit potential oxide-nitride-oxide dielectric oxidized porous silicon photoconductive decay photothermal displacement spectroscopy photoluminescence photoluminescence excitation spectroscopy polymethyl methacrylate passivation potential polypropylene porous silicon phosphosilicate glass porous silicon layer polytetrafluoroethylene polyvinyl chloride polyvinylidene fluoride... 

Another way to use silicon wafers as DLs was presented by Meyers and Maynard [77]. They developed a micro-PEMFC based on a bilayer design in which both the anode and the cathode current collectors were made out of conductive silicon wafers. Each of fhese componenfs had a series of microchannels formed on one of their surfaces, allowing fhe hydrogen and oxygen to flow through them. Before the charmels were machined, a layer of porous silicon was formed on top of the Si wafers and fhen fhe silicon material beneath the porous layer was electropolished away to form fhe channels. After the wafers were machined, the CEs were added to the surfaces. In this cell, the actual diffusion layers were the porous silicon layers located on top of the channels because they let the gases diffuse fhrough fhem toward the active sites near the membrane. 

In a similar design, DArrigo et al. [78] also used porous silicon as the DL in a fuel cell. The porous silicon was deposited by chemical vapor deposition (CVD) on top of a silicon wafer that already had microgrooves machined on it. Then, catalytic particles were deposited on top of fhe porous silicon layer. Unfortunately, no performance-related data indicating whether the cell was acceptable or not were published for fhis design. 

Previous reports 13] emphasized the importance of sample handling, and indeed because of the very volatile nature of the compounds measured in this type of analysis, sample collection deserves special consideration. In general, narrow mouth glass vials with a total volume in excess of 50 ml are acceptable. The bottles need not be rinsed or cleaned with organic solvents, but simply cleaned with detergent and water, rinsed with distilled water, air dried, and dried in a 105°C oven for one hour. The vials are carefully filled with sample to overflowing (zero head space) and a Teflon faced silicone rubber septum is placed Teflon face down on the water sample surface. The septa may be cleaned in the same manner as the vials, but should not be heated more than one hour because the silicone layer slowly degrades at 105°C. 

Australia, and scaled up by BP Solar in Spain, the heterojunction with intrinsic thin layer (HIT) cells developed by Sanyo by replacing the diffused P-doped emitter with an amorphous silicon layer and the back contact cells developed by Stanford University for use in concentrator technology and now converted to a large area for flat plate use. All three use single-crystalline silicon, while the majority of screen-printed cells use multicrystalline silicon wafers. 

Kim SJ, Jeon BH, Choi KS (1999) Improvement of the sensitivity by UV light in alcohol sensors using porous silicon layer. In CAS 99 Proceedings of the international semiconductor conference, Sinaia, Romania, 2 475 78... 

SorU B, Garcia M, Benhida A et al (1999) Porous silicon layer used as a humidity sensor. In Proceedings of the european matter conference E-MRS spring meeting. Symposium 1 micro-crystalline and nanocrystaUine semiconductors, 1-8... 

Cl2) or hydrogen chloride (HC1). The silane gas has to be diluted with an inert gas to prevent precipitation in the gas phase. In addition, small amounts of phosphane PH3 or diborane B2H6 can be added to dope the deposited silicon layer. 

W. Moritz, T. Yoshinobu, F. Finger, S. Krause, M. Martin-Fernandez and M.J. Schoning, High resolution LAPS using amorphous silicon as the semiconductor material, Sens. Actuators B Chem., 103 (2004) 436—441. J.C. van den Heuvel, R.C. van Oort and M.J. Geerts, Diffusion length measurements of thin amorphous silicon layers, Solid State Commun., 69(8) (1989) 807-810. 

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