Semiconductors electrical resistivity, variation with

The thermisters (TMs) are semiconductor device with a high resistance dependence on temperature. They may be calibrated as a thermometer. The semiconductor sensor exhibits a large change in resistance that is proportional to a small change in temperature. Normally TMs have negative thermal coefficients. Like RTDs, they operate on the principle that the electrical resistance of a conductive metal is driven by changes in temperatures. Variations in the conductor s electrical resistance are thus interpreted and quantified, as changes in temperature occur. 

As was remarked as early as chap. 1, many of the properties of materials are not intrinsic in the sense that they are highly dependent upon the structure, purity and history of the material in question. The electrical conductivity is one of the most striking examples of this truth. Nowhere is this more evident than in considering the role of doping in semiconductors. This is hinted at in fig. 7.2 where it is seen that the conductivity of Si ranges over more than 6 orders of magnitude as the concentration of impurities is varied. In fig. 7.3 this effect is illustrated concretely with the variation in resistivity of Si as a function of the concentration of impurities. 

Figure 5.9 shows the variation in resistivity of three metals with temperature. In each case, p increases with temperature, and the electrical conductivity (which is the inverse of the resistance) decreases as the temperature is raised. This property distinguishes a metal from a semiconductor, which is a material in which the electrical conductivity increases as the temperature increases (Figure 5.10). 

Semiconductor nano element devices show great promise, potentially outperforming standard electrical, opt-electrical, and sensor- etc. semiconductor devices. These devices can use certain nano element specific properties, 2-D, 1-D, or 0-D quantum confinement, flexibility in axial material variation due to less lattice match restrictions, antenna properties, ballistic transport, wave guiding properties etc. Furthermore, in order to design first rate semiconductor devices from nanoelements, transistors, light emitting diodes, semiconductor lasers, and sensors, and to fabricate efficient contacts, particularly with low access resistance, to such devices, the ability to dope and fabricate doped regions is cracial [66, 67]. 

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