Impurity concentration profile

Fig. 7. (a) Impurity elements are rejected into the Hquid between the dendritic solidification fronts, (b) Corresponding impurity concentration profiles. Cq, weld metal composition k, impurity partitioning coefficient in the Hquid maximum impurity soHd solubiHty eutectic composition at grain... 

Fig. 3. Impurity concentration profiles resulting from progressive freezing with different values of distribution coefficient k (from eq. 2).

Fig. 7. Constitutional supercooling, (a) impurity concentration profile during solidification (b) actual temperature T and equilibrium freezing temperature T...

A certain relationship, which exists between the bulk and surface properties of semiconducting materials and their electrochemical behavior, enables, in principle, electrochemical measurements to be used to characterize these materials. Since 1960, when Dewald was the first to determine the donor concentration in a zinc oxide electrode using Mott-Schottky plots, differential capacity measurements have frequently been used for this purpose in several materials. If possible sources of errors that were discussed in Section III.3 are taken into account correctly, the capacity method enables one to determine the distribution of the doping impurity concentration over the surface" and, in combination with the layer-by-layer etching method, also into the specimen depth. The impurity concentration profile can be constructed by this method. It has recently been developed in greatest detail as applied to gallium arsenide crystals and multilayer structures. 

Impurity concentration profiles can be shaped to certain specifications. One important aspect of ion implantation into semiconductors, in contrast to the diffusion process, is that the number of implanted atoms can be precisely controlled by the external system, rather than by the physical parameters of the target material. 

Ion implantation is well suited for the design of bipolar structures used in injection logic. Among the attributes of ion implantation for these are 1) ability to fabricate shallow devices thus improving the speed and gain and tailoring the impurity concentration profiles. Separate implantations for the inactive and the active base layers are usually desirable. 

Figure 20. Impurity concentration profile of a bipolar transistor fabricated by diffusion. (Reproduced from Reference 41).

An investigation was made of diffusion into (lll)-type samples by using the spreading resistance technique to determine impurity concentration profiles. It was... 

As seen from equation (27) the surface concentration of impurity ions depends critically on the difference in binding at the surface from the bulk. The space charge concentration of divalent ions on the other hand depends mainly on the sign of the surface electrostatic potential. Thus, various impurity concentration profiles are possible i.e., enriched/depleted surface monolayers combined with enriched/depleted space charge regions. As discussed later experimental surface analytical techniques have difficulty in distinguishing these possibilities. 

Figure 6.3.15. (a) Zone melting impurity concentration profile in melt near the freezing interface (b) a small element in the molten zone illustrating various fluxes (coordinate system based on part (c)) (c) overall configuration in a coordinate system fixed in the heater. 

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