Functional Materials and Advanced Manufacturing

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57 Amorphous Semiconductors

The relations (3.5a) and (3.5b) clearly show that the electron–photon system obeys

the conservation laws of both momentum and energy. In Equation 3.5a, E

initial

and

E

nal

are the electron energies before and after the electronic jump. In Equation 3.5b

p

initial

andp

nal

are the corresponding momenta of electron. The symbol “ℏ” is (1/2π)

times the Planck’s constant while the symbol “k” represents the propagation con-

stant of the photon absorbed in the process. Physically, it is the magnitude of wave



vector k of the photon. In general, the value of k of a photon is extremely small in