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32 {\LARGE {\bf Materials Physics I}\\}
37 {\Large\bf Tutorial 6}
40 \section{Indirect band gap of silicon}
42 Some facts about silicon:
44 \item Lattice constant: $a=5.43 \cdot 10^{-10} \, m$.
45 \item Silicon has an indirect band gap.
47 \item The minimum of the conduction band is located at
48 $k=0.85 \frac{2 \pi}{a}$.
49 \item The maximum of the valance band is located at $k=0$.
50 \item The energy gap is $E_g=1.12 \, eV$.
54 \item Calculate the wavelength of the light necessary to lift an electron from
55 the valence to the conduction band.
56 What is the momentum of such a photon?
57 \item Calculate the phonon momentum necessary for the transition.
58 Compare the momentum values of phonon and photon.
59 \item Draw conclusions concerning optical applications.