2_1_class8sllides

2_1_class8sllides - EE 2 Fall 2007 Class8slides 1 1 2 3 4 5...

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1 EE 2 Fall 2007 Class 8 slides
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2 1. Review of last class 2. Intrinsic semiconductor 3. Distribution of electrons in the conduction band 4. Temperature dependence of carrier concentration 5. Distribution of holes in the valence band 6. Location of Fermi energy in the band gap in an intrinsic semiconductor
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3 Review of last class We discussed the consequences of band theory and the resulting properties of carriers in filled band and partially filled band. We saw the distinction among metals, insulators and semiconductors. We discussed how we can treat the electrons as though they are free particles with an effective mass
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4 Intrinsic semiconductor An intrinsic semiconductor is one which is pure without any impurities and electrons are excited to the conduction band from the valence band by thermal excitation. For each electron that is excited to the conduction band there is generated a hole in the valence band. The electron density (#cm -3 ), also called concentration, is denoted by the letter ‘n’ and the hole density by the letter ‘ p ’. We denote the carrier density with a subscript i as in n i and p i, when we discuss the carrier concentration in an intrinsic semiconductor. The electrons in the conduction band and the holes in the valence band can be treated as free particles and we can use the distribution functions we derived for free electrons in a box for calculating the dynamic properties of the electrons and holes.
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5 Intrinsic semiconductor In applying the free electron (electrons in a box) approximation to
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