Gases dopant

By varying the partial pressure of the gas phase of the dopant in the furnace, the concentration of impurities in the silicon can be changed. Henry s law relates the concentration of dopants that are introduced in the furnace to the surface concentration by the relation C0 = HpSf where C0 is the surface concentration of dopant, H is Henry s constant, and p is the partial pressure of the dopant gas. 

Figure 1 is a plot of boron concentration versus ps that illustrates Henry s law. When the solid solubility of boron in silicon is reached, Henry s law no longer applies. Thus, most predeposition steps are operated at a sufficiently high partial pressure in the dopant gas phase to achieve solid solubility of the dopant in the silicon. This requirement provides a natural control for reproducible diffusion results. 

The Gaussian distribution can be used to describe the impurity profile that results from a drive-in step with no dopant gas in the furnace. The drive-in step itself is performed in several types of ambients dry oxygen, steam, nitrogen, or argon. The drive-in temperatures range from 900 to 1200 °C. 

Fay et al. [3] used a pressure lower than 1 Torr, but also BoHf, as dopant gas. They, however, did not observe any substantial modification of crystal orientation by doping. Indeed, as illustrated in Fig. 6.35b, the (1120)/(1010) peak ratio observed here is quite high for undoped ZnO films deposited at 155°C, and remains at a high value even when the dopant concentration is increased. Moreover, in this case, the deposition rate does not vary significantly with the introduction of I >21 h , as is shown in Fig. 6.36. 

The procedure is the same as for depositing polysilicon except that there is an additional flow of the dopant gas. For example, for the incorporation of phosphorous, which of various possible impurity dopants has been the most extensively studied to date, phosphine diluted in an inert gas, such as nitrogen, is introduced into the reactor. The overall process can be represented by... 

In fact, other reactions are added as a result of the introduction of dopant gas like boron or phosphorus precursors that are used to modify the electrical... 

In the case of in-situ doping during epitaxy, a small amount of dopant gas is introduced into the reactor at the same time as the silicon precursor. The... 

The actual incorporation of dopants in silicon is determined by a factor of segregation Keg. It is given by the concentration of dopants in silicon divided by the ratio of partial pressure of dopant gas (Pgopant) and silicon precursor... 

On the one hand, when Keg is less than 1, part of the incorporated dopant atoms are rejected from the silicon layer. On the other hand, when Keg is equal to 1, the atoms of the dopant gas are completely incorporated in the silicon. 

In the regime limited by the surface kinetics, adding a dopant gas to induce n-type or p-type doping causes an increase in the growth rate. On the contrary, in the regime limited by mass transfer, adding dopants in the reactive gas does not affect the silicon growth rate [16-18]. 

A method for reducing the dopant concentration loss on the surface is to cover the surface with an oxide layer, the latter acting as diffusion barrier [19]. Another method is to carry out the cooling step under a dopant gas flow, in such a way that the gas phase is saturated with boron or phosphorus. This trick helps ensuring a uniform doping along the volume of the epitaxial layer. 

Since the introduction of ECD, the Ni 3-ray radioactive electron source has remained unchanged, and considerable efforts have been made to develop nonradioactive alternatives. A new version of such a detector — the pulsed discharge electron capmre detector (PDECD) — employs a pulsed discharge in helium as the primary source of electron generation. A modified version of PDECD which makes use of methane as the dopant gas and of a sapphire and quartz insulation was used for detecting OCPs. The relatively low ionization potential of methane allows reduction... 

The electronic structure of a doped semiconductor is shown here, (a) Which band, A or B, is the valence band (b) Which band is the conduction band (c) Which band consists of bonding molecular orbitals (d) Is this an example of an n-type or p-type doped semiconductor (e) If the semiconductor is germanium, which of the following elements could be the dopant Ga, Si, or P [Section 12.7]... 

One method of making n-doped Si for solar cells is to pass a dopant gas mixture of phosphine and oxygen over the silicon surface at about 800°C. Some surface oxidation of the silicon takes place, and the resultant silica reacts with the P2O5 formed according to (12.402) to form a glass layer, which becomes the diffusion source. 

FIGURE 21.9 Mass spectra of RDX. (A) Without any dopant gas, (B) with dichloromethane dopant, and (C) with lactic acid dopant. 

Other hand, LA was tested as a dopant gas as illustrated in Figure 21.10B. The ion signal of m/z 311 becomes a dominant signal with a low concentration of LA, and 15 ppm of LA is enough to obtain a strong signal of the adduct ions. 

Dopant gas/semiconductor A gas or gas mixture used to incorporate a metallic impurity into a semiconductor substrate to impart particular electrical properties. 

While a concern, there have been no published reports of significant dopant gas exposures during oil changes of vacuum pumps used with dopants—possibly because this is usually done as a closed system. The lack of reported exposure may also be a result of low levels of off-gassing of hydrides fi om the used oil. 

Diachem electrodes are manufactured by HFCVD with methane and dopant gas (diborane or trimethylboron)... 

Linear dynamic response ranges for capillary (IC-AED extend from the upper linear analyte-carr3ring column capacity, at ca.l00 ng, down to the detection limit for the element (1-100 pg). Chemical, dopant gas and plasma-wall interaction effects modify the limits. 

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