Dopant impurity

The stmcture of the polysihcon depends on the dopants, impurities, deposition temperature, and post-deposition heat annealing. Deposition at less than 575°C produces an amorphous stmcture deposition higher than 625°C results in a polycrystalline, columnar stmcture. Heating after deposition induces crystallization and grain growth. Deposition between 600 and 650°C yields a columnar stmcture having reasonable grain size and (llO)-preferred orientation. 

At the same time, it was demonstrated that hydrogen neutralization of dopant impurities also occurs in compound semiconductors. This was first achieved with n-type dopants in GaAs (Chevallier etal., 1985) and then with p-type dopants in GaAs (Johnson et al., 1986b). 

Equation 36 is divided into the contributions to the diffusion of substitutional impurity under nonoxidizing conditions, DSI, and the enhanced contribution due to oxidation, AD0. Figure 16 shows the data of Taniguchi et al. (44) for oxidation-enhanced diffusion of P and B versus the total number of dopant impurities per square centimeter, QT. The calculated values of DSI and AD0 are shown in comparison with the experimental data. Reasonable agreement is obtained. Thus, Taniguchi s model of self-interstitial recombination with vacancies is consistent with the models of high-concentration diffusion of B and P used by Fair in his calculations. 

Overall SIMS is the most sensitive and accurate technique for measuring chemical dopants/impurities and composition in the nitride material system. However, this is destructive and cannot provide fast feedback to the crystal grower. Complementary techniques such as XRD, PL and RHEED can therefore be used to determine the composition of alloys with reduced accuracy. 

Structural effects the free volume model. Demonstrative examples of the role of free spaces on Ps formation in solids are provided by solids in which no Ps is formed when pure, and where the Ps yield increases as some dopant impurity is added. This is the case for p-terphenyl, in which the Ps yield increases as either chrysene or anthracene are added. Both dopant molecules, when introduced in the p-terphenyl matrix, promote the formation of extrinsic defects having roughly the size of a naphthalene molecule [42], Similarly, doping the ionic KIO4 matrix by lOj ions induces the formation of oxygen vacancies which promote the formation of Ps [43],... 

Catalytic applications of ceria and ceria-based mixed oxides depend primarily upon the nature and concentration of the defects present in the material. Although experimental techniques are available for the study of these defects, the characterization of their physical properties at the atomic level is often very difficult. The most important point defects in ceria are oxygen vacancies, reduced Ce centers and dopant impurities. The formation energy of such defects and the energetics of their mutual interactions within the bulk oxide have been the subject of several computational studies. 

Russel Ohl of Bell Laboratories discovered and filed patents in 1941 that were granted in 1946 and 1948 " for the p-n junction photovoltaic effect in silicon. The early devices contained rectifying junctions that were accidentally formed by segregation of dopant impurities during cooling. 

Extrinsic diffusion is controlled by dopants (impurities) that are present. 

As shown in Fig. 9.18, there is a quite uniform deposition of copper on both n-and p- germanium substrates. However, these images clearly show that larger particles of Cu are produced on n- germanium substrates in comparismi to that of the p-Ge, leading in this way to a different surface morphology. The differences in the surface morphology of these two samples were attributed to the presence of different dopants (impurities) in the n- and p- Ge substrates [12]. 

There are several challenges associated with the synthesis of BDD suitable for electrochemistry. Since diamond is a semiconductor with exceptional properties, precise control of dopant impurities and extended defects is required to dope the diamond lattice with sufficient boron to make the material conduct. However, as the boron levels increase, it can be harder to maintain crystallinity and control the amount of nondiamond carbon (NDC) both within crystal defects and at grain boundaries. While NDC can increase material conductivity, it is be detrimental to a diamond electrochemist, as the widely recognized electrochemical properties of BDD (wide solvent window, low background currents, reduced susceptibility to electrode fouling, corrosion resistance) are impaired and the electrochemical response becomes more akin to glassy carbon. If the presence of NDC is unaccounted for, electrical resistivity measurements will mislead the user into believing that there is more boron than actually present in the matrix. 

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