Silicon undoped

The fact that pure silicon is not a conductor but is "doped to make it a good semi-conductor might seem odd, particularly since considerable effort goes into obtciining very pure silicon. Nonetheless, the undoped silicon is not conductive. This allows one to form discrete areas of n-type and p-type silicon on the same wafer and to position these in conjunction with each other in a manner so that a current amplifying device results. An example of such a device is shown in the following diagram ... 

The corona discharges produces oxygen ions and ozone, which may react with the photoconductor [634], As a means to circumvent possible degradation of the surface layer, an extra, protective thin layer was proposed, with high carbon content [101, 635, 636]. This would reduce silicon-oxygen reactions at the surface. Excellent electrophotographic characteristics have been obtained with a thin device comprising a 0.1-/rm-thick n-type a-Si H layer, a 1.0-/rm intrinsic a-Si H layer, a 0.1-/irm undoped a-SiCo i H layer, and a 0.014-/xm undoped a-SiCoj H layer [101]. 

Evidence is presented for continuous tuning of the band-filling between y - 0.00 and 0.50. In comparison, electrochemical oxidation of monoclinic /)-Ni(Pc) under the same conditions is also accompanied by a significant overpotential in forming tetragonal Ni(Pc)-(BF4)0.48- However, electrochemical undoping produces the monoclinic 7-Ni(Pc) phase with far less band structure tunability than in the silicon polymer. Experiments with tosylate as the anion indicate that tetragonal [Si(Pc)0](tosylate)y n can be tuned continuously between y = 0.00 and 0.67. For the anions PFg,... 

DIFFUSION COEFFICIENT ACTIVATION ENERGY AND PREEXPONENTIAL FACTOR FOR UNDOPED AMORPHOUS SILICON... 

Doped silicon, conductivity in, 23 35 Doped/undoped electrochromic organic films, 6 580-582 Dope-dyeing, 9 197 Dope-making process, in acrylic fiber solution spinning, 11 204 Dope solids, in air gap spinning, 11 209 Doping, 23 838—839 calcium, 23 842-844 conducting polymers, 7 528-529... 

In traditional semiconductors such as silicon, germanium, or Ga2As3 the conductivity is between, say, 10 to 10 cm In an undoped solid, the concentration of free charge carriers is determined by n = where Aeff is... 

Conductivity in doped silicon crystals is determined by the properties of the added charge earners or majority earners. In n-type silicon, electrons are majonty carriers and holes are minority carriers. There are fewer holes in n-type silicon than in undoped silicon because the large number of electrons causes some recombination with preexisting holes. In p-type silicon, holes are the majonty earners and electrons are the minority carriers. Fewer electrons are present in p-type silicon than in undoped silicon because of the recombination of some electrons with the enhanced population of holes. 

The first step in the fabrication of modern bipolar integrated circuits is the creation of heavily-doped islands in the silicon substrate within which to fabricate the circuits. In the process of creating these "buried layers," the area they occupy has a surface that lies somewhat below the surface of the undoped substrate. The typical appearance of such a buried layer is illustrated in Figure 21. 

Furthermore, a series of ZnO B films with various doping levels has been deposited, and the thickness of the films has been adapted so as to keep the sheet resistance close to 10Qsq. This means that the thickness of the ZnO films was increased as their doping level was decreased. For this series, the highest FoM(A) of LP-CVD ZnO films on the whole visible spectral range has been obtained for the 6 j,m-thick undoped film. This prediction has then been experimentally confirmed the same microcrystalline silicon solar cell was deposited on this ZnO series, and the highest photogenerated current... 

As described in Volume 2IB, Hydrogenated Amorphous Silicon Optical Properties, the absorption coefficient of undoped a-Si H is strongly influenced by the deposition conditions. For example, the optical gap usually increases as the substrate temperature decreases, and this effect has been attributed to an increase in the hydrogen content (Zanzucchi et al.,... 

In a-Si H, it is difficult to operate CCDs in the same mode as conventional SCCDs. This is because the ideal inversion at the p-type a-Si interface has not been observed as yet (Sugiura and Matsumura, 1982), and as for H-type a-Si H, whose interface can be inverted, the drift mobility of the signal charge (i.e., hole) is very low. However, the band gap of a-Si H is about 1.7 eV, which is much wider than that of a single-crystal silicon. This indicates that the carrier concentration in undoped a-Si H under thermal equilibrium condition is so low that the accumulation mode can store transient signals sufficiently long for CCD operation, as described later. 

A physical model for the formation energies is more easily addressed for undoped a-Si H because the dopants do not have to be included. The origin of the distribution is the disorder of the silicon network. Defect generation is expected to occur when a silicon-silicon bond... 

Light sensors made from a-Si H are either p-i-n or Schottky barrier structures. Unlike crystalline silicon, a p-n jimction is ineffective without the undoped layer, because of the high defect density in doped a-Si H. Illumination creates photoexcited carriers which move to the junction by diffusion or drift in the built-in potential of the depletion layer and are collected by the junction. A photovoltaic sensor (solar cell) operates without an externally applied voltage and collection of the carriers results from the internal field of the junction. When the sensor is operated with a reverse bias, the charge collection generally increases and the main role of the doped layers is to suppress the dark current. A Schottky device replaces the p-type layer with a metal which provides the built-in potential. 

It is noted that the polishing of the polysilicon film will employ the well-known technology of polishing monocrystalline silicon substrates. This gives an opportunity to examine the effect of polycrystallinity and thus of grain boundaries and grain orientation in CMP of Si. Doped vs. undoped polysilicon will also shed... 

In the semiconductor technology area most of the experience has been accumulated from research and development in cleaning the silicon substrates. For CMP technologies a variety of additional materials are involved — insulators (like SiOj. doped SiOj, and polymers), high dielectric constant materials (like BaTiOj), polysilicon (doped or undoped), silicides to form low resistivity gate interconnections on top of doped polysilicon, metals (like Cu and Al, and their alloys, W, metal-nitrides, and Ta), silicon nitride, and many others, some of which have been discussed in earlier chapters. Thus cleaning processes must be... 

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