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Unformatted text preview: energy is given as 2 ⎛ π ⎞
E=
⎜ ⎟ = 2.14 eV . 2m ⎝ a ⎠
2 At the top of the gap, we have αa ~ 1.7, so that 2 ⎛ 1.7π ⎞
⎜
⎟ = 6.18 eV 2m ⎝ a ⎠
2 E= and the forbidden gap is EG = 6.18 − 2.14 = 4.04 eV . (b) At ka = 2π, αa has the same value, so the energy is given as 2 ⎛ 2π ⎞
E=
⎜
⎟ = 8.55 eV . 2m ⎝ a ⎠
2 At the top of the gap, we have αa ~ 2.6, so that 2 ⎛ 2.6π ⎞
⎜
⎟ = 14.45 eV 2m ⎝ a ⎠
2 E= and the forbidden gap is...
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This document was uploaded on 02/19/2014.
 Fall '14

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