hw5_sol - 3.091 Homework #5 page 2 1. Each In atom will...

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3.091 Homework #5 page 2 1. Each In atom will attract an electron and thus create a “mobile hole”; we only have to determine the number of In atoms/cm 3 . The atomic volume of the host crystal (Ge) is given on your PT as 13.57 cm 3 /mole. (a) # Ge atoms/cm 3 = 23 3 6.02 10 atoms 1 mole 1 mole 13.57 cm × × = 4.44 × 10 22 atoms/cm 3 # In atoms/cm 3 = 4.44 × 10 22 × 0.0003 × 10 -2 = 1.33 × 10 17 In/cm 3 The number of free charge carriers (“holes”) is 1.33 × 10 17 /cm 3 ; they are created through the acquisition of one electron by each In atom from the valence band of the host crystal. (b) conduction band valence band +. . . .+ In . . . . In 1.33 × 10 17 In ions in the band gap just above the valence band edge. 1.33 × 10 17 holes in the valence band E g =0 .7eV acceptor level for In 2. λ crit = hc E g = 6.62 × 10 34 × 3 × 10 8 1.1 × 1.6 × 10 19 = 1.13 × 10 6 m The critical λ for silicon is 1.1 × 10 -6 m; thus radiation of λ = 5 × 10 -7 m = 0.5 × 10 -6 m has even more energy than that required to promote electrons across the band gap.
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This note was uploaded on 11/02/2009 for the course CHEMISTRY 3.091 taught by Professor Donsadoway during the Fall '04 term at MIT.

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hw5_sol - 3.091 Homework #5 page 2 1. Each In atom will...

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