Diffusion of impurities

Note in passing that the common model in the theory of diffusion of impurities in 3D Debye crystals is the so-called deformational potential approximation with C a>)ccco,p co)ccco and J o ) oc co, which, for a strictly symmetric potential, displays weakly damped oscillations and does not have a well defined rate constant. If the system permits definition of the rate constant at T = 0, the latter is proportional to the square of the tunneling matrix element times the Franck-Condon factor, whereas accurate determination of the prefactor requires specifying the particular spectrum of the bath. 

Because diffusion of impurities in SiC is impractical, SiC DIMOSFET cannot be fabricated using self-aligned processes adopted from the Si industry. On the other... 

The damage and high concentrations of lattice delects, resulting from atomic displacements produced by the incident alums, can change the chemical reactivity and mechanical hardness of a treated surface, Implantation cun enhance the diffusion of impurities already deposited in a substrate, presumably through the motion of the high concentrations of lattice defects produced by the incident ions. 

The Role of Point Defects in Silicon Processing. The Balancing Act in Silicon Processing. Both silicon oxidation and the diffusion of impurities occur at high temperatures and involve point defects such as va-... 

After the balance sheet of pros and cons surrounding the question of the native defect in Si is reviewed, the question remains. What is the native defect responsible for the diffusion of impurity and growth of defects in Si So far we only have clues. 

FIGURE 4 SIMS profile of a GaN layer grown by MBE on a GaP substrate showing diffusion of impurities from the substrate and the accumulation of impurities at the layer/substrate interface. 

To illustrate the use of PIXE and micro-PIXE in the study of breakdown phenomena in polyethylene high voltage cable insulation and other related topics we will describe a few typical measurements, first the study by standard PIXE of impurities in the organic semiconductor H2PC and in the carbon black semicon used in high voltage cables. Examples of the use of the microbeam to study some electrical and water trees as well as the diffusion of impurities from the semicon into polyethylene under typical electric field and humidity conditions will be given. 

Refining by slag treatment is dependent on several parameters, such as reaction kinetics, diffusion of impurities, partition ratios, etc. Meanwhile, these parameters are dependent on the type of slag and its thermophysical and thermochemical properties. For example, viscosity, density, and interfacial properties affect the separation of slag from the metal and the duration of slag refining. 

Assuming that there is thermodynamic equilibrium at the solid/liquid interface, no diffusion of impurities in solid, and complete mixing in the liquid,... 

Simultaneous with the carburization reaction, a diffusion of impurity element traces takes place. It can be assumed that these atoms migrate preferably along grain boundaries... 

With the machinery of transition state theory in place, it is now possible to examine the predicted diffusion rates associated with a host of different important situations ranging from the bulk diffusion of impurities to the motion of adatoms on surfaces to the short-circuit diffusion of atoms along the cores of dislocations. It is evident that besides being of academic interest (which they definitely are), diffusive processes such as those mentioned above are a key part of the processing steps that take place in both the growth and subsequent microstructural evolution of the materials around which modern technology is built. 

Diffusion of impurity atoms in bulk substrate under the porous layer is fairly different from diffusion of the same species in nonporous crystals. Figure 2.16 shows boron atom profiles in bulk substrate under the porous layer (formed at the same conditions) after diffusion at different temperatures. Coordinate x = 0 corresponds to the interface porous layer-bulk substrate. The diffusion profile of boron atoms in nonporous SiC substrate after diffusion at the same conditions (2000 °C, 10 min) is also presented in this plot for comparison. It is seen that the maximum concentration of boron atoms diffused from the porous layer into bulk... 

The diffusion of impurities into Si wafers typically is done in two steps. In the first step, dopants are implanted into the substrate to a relatively shallow depth of a few thousand angstroms. After the impurities have been introduced into the Si substrate, they are diffused deeper into the substrate to provide a suitable impurity distribution in the substrate. The solid solubility and diffusion of dopant atoms in Si are given in the top and bottom, respectively, of Fig. 9.10. 

---