Normalized plot of n0/ND as a function of temperature. This plot is for ND = 1016 cm3.

Figure 2.20

2-20

Under high doping concentrations, the formerly discrete donor levels smear into a band, effectively narrowingthe band gap by an amount Eg.

Figure 2.21

2-21

Reduction of room-temperature band gap Eg as a function of donor density in phosphorus-doped silicon.

Figure 2.23

2-23

The motion of an electron in a crystal. The electron changes direction randomly whenever it makes a collision.(a) Under no applied field there is no net progress in any particular direction. (b) When a field is applied, theelectron tends to drift in some particular direction. A trajectory such as this would be found only under veryhigh fields.

Figure 3.1

3-1

3-9

Mobility as a function of temperature. At low temperatures, impurity scattering dominates, but at hightemperatures, lattice vibrations dominate.

Figure 3.8

3-10

The experimentally measured dependence of the drift velocity on the applied field.

Figure 3.9

3-13

Various generation and recombination processes. (a) An electron-hole pair is generated when an electronabsorbs (in this case) a phonon plus a photon. This generation could also occur by the absorption of a singlephoton or multiple phonons. The photons and phonons are absorbed simultaneously. (b) Band-to-bandrecombination via the simultaneous emission of multiple phonons. (c) A two-step generation process, in which, for example, the electron absorbs a phonon to promote it to the acceptor state, then in the next step it absorbsa photon to go to the conduction band. (d) A typical recombination event in p-type material involves emissionof a photon to take the electron temporarily to the acceptor level, then the subsequent emission of the phononreturns it to the valence band, annihilating a hole. (e) and (f) Recombination and generation via trap states.

Figure 3.12

3-14

(a) At equilibrium, electrons and holes are generated and destroyed at equal rates, thus maintaining someconstant equilibrium n0 and p0. (b) When light shines on the sample, the photons can be absorbed, producingextra electron-hole pairs.

Figure 3.13