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Figure 2.7. The light energy dependency of electron-hole generation.
The generation rate (G) of electron-hole (e-h) pairs per unit volume can be calculated
using the formula:
G Į Ne x Į (2.1)
where N is the photon flux (photons per unit area per second), Į is the absorption
coefficient, and x is the distance from the surface. The value of Į as a function of the
wavelength of light is illustrated in Fig. 2.8 for silicon at 300 K.
Figure 2.8. The absorption coefficient, Į, of silicon at 300 K as a function of the
vacuum wavelength of light.
2.4 RECOMBINATION
When the light is switched off, the system must return to a state of equilibrium and
the electron-hole pairs generated by the light must disappear. With no external source
of energy, the electrons and holes wander around until they meet up and recombine.
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