Semiconductor, intrinsic, definition

Figure 9.1 Band model of an intrinsic semiconductor and definition of energies. is the electron affinity, the work function, and the gap energy.

The above definition is actually that for intrinsic semiconductors. What make semiconductors so useful in electronics, however, is that their electronic properties can be altered in a controllable manner by adding tiny amounts of an advisedly chosen impurity. This is the well-known process of doping, which is related to the notion of extrinsic semiconductors. 

Fig. 3.15 Band model for an intrinsic semiconductor. The valence band is totally filled and the conduction band empty. Conduction occurs via promotion of electrons from Ey to Ecy the conductivity increasing with increase in temperature, (a) Definition of energy levels (b) Variation of density of available states with...

The double- and single-escape peak efficiencies are used with semiconductor detectors only. In the above definitions, if the total detector efficiency is replaced by intrinsic, the corresponding full-energy, single-, and double-escape peak efficiencies are also considered intrinsic. 

In metals the Fami energy is the enetgy of the highest occupied energy level (at T = 0 K). In an intrinsic semiconductor the Fermi energy is per definition midway between the valence and conduction bands. Therefore, the Fermi energy for an intrinsic semiconductor is... 

We now describe the behavior of charge carriers in an intrinsic semiconductor (i.e., pure) at equilibrium. The electrical properties of any extended solid depend on the position of the Fermi level, defined as the highest occupied state at T = 0 K. An alternative definition, stemming from the Fermi-Dirac statistics that govern the distribution of electrons, the Fermi level is the energy at which the probability of finding an electron is If the Fermi level falls within a band, the band is partially filled and the material behaves as a conductor. As shown in Fig. 3, the valence and conduction band edges of an intrinsic semiconductor straddle the Fermi level. At T = 0 K, no conduction is possible since all of the states in the valence band are completely filled with electrons while aU of the states in the conduction band are empty. 

Definite collection volumes can be achieved in PIN diodes, where an undoped zone I of an intrinsic semiconductor separates the p- and -regions (Fig. 4.97). Since no space charges exist in the intrinsic zone, the bias voltage applied to the... 

Definite collection volumes can be achieved in PIN diodes, where an undoped zone I of an intrinsic semiconductor separates the p- and -regions (Fig. 4.95). Since no space charges exist in the intrinsic zone, the bias voltage applied to the diode causes a constant electric field, which accelerates the carriers. The intrinsic region may be made quite wide, which results in a low capacitance of the p n junction and provides the basis for a very fast and sensitive detector. The limit for the response time is, however, also set by the transit time r = ru/uth of the carriers in the intrinsic region, which is... 

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