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# samp25 - m 3/phosphorus = 3 22/m phosphorus 10 5 1 × = 2...

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SAMPLE PROBLEM (Class 25) Suppose that one of every 10 6 silicon atoms in pure silicon is replaced by a phosphorus atom. On average, how far apart will the phosphorus atoms be? ANS: Sample problem 42-6, on page 1049 shows that the number of silicon atoms per cubic meter in pure silicon is, 5 ×10 28 silicon/m 3 . If one of every 10 6 atoms is replaced by phosphorus, there will be: osphorus silicon/ph 10 1 silicon/m 10 5 6 3 28 × × = 5 ×10 22 phosphorus/m 3 . Then on average, each phosphorus atom would occupy a volume equal to:
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Unformatted text preview: m 3 /phosphorus = 3 22 /m phosphorus 10 5 1 × = 2 ×10-23 m 3 . Imagine that the volume is a cube, so the length of an edge would be: nm. 27 m 10 7 . 2 m 10 2 8 3 3 23 = × = × =--a This is the average distance between the phosphorus atoms in the doped silicon. It is about 100 times greater than the average distance between silicon atoms in the same material....
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