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Unformatted text preview: 1 Semiconductors Intrinsic Si Si Si Si Si Si Si Si Si Si Si Si e e e e C E V E h h h h i n N-material Si Si Si Si Si P Si Si Si e e e e C E V E donor E with minimum thermal energy this becomes a free electron D N Æ density of Donor atoms like P . Available free electron (N Æ negative) Æ material is still neutral since –ve charged electron cancels positively charged P ion. P-material Si Si Si Si Si In Si Si Si Si Si Si h h h h C E V E with minimum thermal energy an electron can be absorbed to this bond (p Æ positive) material is still neutral. a E cceptor A N Æ density of acceptor atoms like In . 2 D N n = Å in an N-material A N p = Å in an P-material Turns out that the density of the other carries goes down i.e. in N-material: ⎪ ⎩ ⎪ ⎨ ⎧ = = D i D N n p N n 2 Æ Density of free electrons or holes of an intrinsic semiconductor i n In P-material: ⎪ ⎩ ⎪ ⎨ ⎧ = = A i A N n n N p 2 i n = depends on how much thermal energy is available (Temperature dependent) at 27°C (300K)...
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- Fall '10
- Electron, Electric charge