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  • The typical ionisation energy of a donor in silicon isOption: 1 10.0 eVOption: 2 1.0 eV

The typical ionisation energy of a donor in silicon is

Option: 1

10.0 eV


Option: 2

1.0 eV


Option: 3

0.1 eV


Option: 4

0.001 eV


Answers (1)

best_answer

When donor impurity (+5 valence) added to a pure silicon (+4 valence), the +5 valence donor
atom sits in the place of + 4 valence silicon atom. So it has a net additional + 1 electronic
charge. The four valence electron form covalent bond and get fixed in the lattice. The fifth
electron (with net – 1 electronic charge) can be approximated to revolve around + 1 additional
charge. The situation is like the hydrogen atom for which energy is given by \mathrm{E=-\frac{13.6}{n^2} e V}.. For
the case of hydrogen, the permittivity was taken as \mathrm{\varepsilon_{0}}.  However, if the medium has a permittivity \mathrm{\varepsilon}, relative to \mathrm{\varepsilon_{0}}. then \mathrm{E=-\frac{13.6}{\varepsilon_r^2 n^2} e V} 

For Si, \mathrm{\epsilon _{r}=12} and for \mathrm{n=1, E=0.1 \mathrm{eV}}

 

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