Intrinsic semiconductors

Intrinsic semiconductors are semiconductors, which do not contain impurities. They do contain electrons as well as holes. The electron density equals the hole density since the thermal activation of an electron from the valence band to the conduction band yields a free electron in the conduction band as well as a free hole in the valence band. We will identify the intrinsic hole and electron density using the symbol ni, and refer to it as the intrinsic carrier density.

Intrinsic carrier density
Intrinsic semiconductors are usually non-degenerate, so that the expressions for the electron and hole densities in non-degenerate semiconductors apply. Labeling the
Fermi energy of intrinsic material as Ei, we can then write two relations between the intrinsic carrier density and the intrinsic Fermi energy, namely:



It is possible to eliminate the intrinsic Fermi energy from both equations, simply by multiplying both equations and taking the square root. This provides an expression for the intrinsic carrier density as a function of the effective density of states in the conduction and valence band, and the bandgap energy Eg = Ec - Ev.



The temperature dependence of the intrinsic carrier density is dominated by the exponential dependence on the energy bandgap. In addition, one has to consider the temperature dependence of the effective densities of states and that of the energy bandgap. A plot of the intrinsic carrier density versus temperature is shown in Figure 2.6.4.


Figure 2.6.4: Intrinsic carrier density versus temperature in gallium arsenide (GaAs), silicon and germanium. Compared is the calculated density with (solid lines)
and without (dotted lines) the temperature dependence of the energy bandgap.  

Estudiante:

Leonardo Andrés Márquez Fernández.

Electronica del Estado Sólido.

Fuente: http://ecee.colorado.edu/~bart/book/book/

---

Get news, entertainment and everything you care about at Live.com. Check it out!