# Sol1 - ECE 255 ELECTRONIC ANALYSIS AND DESIGN Homework 1...

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ECE 255 ELECTRONIC ANALYSIS AND DESIGN Fall 2009 Homework 1 Solutions Problem 1 (Text 2.12) (a) A voltage of 5 V is applied across a 10 μ m long region of silicon. What is the electric field? 5V V E 5000 10 m cm Voltage Distance = = = μ (b) Suppose the maximum field allowed in silicon is 10 5 V/cm. How large a voltage can be applied to a 10 μ m long region of silicon? ( 29 5 V V E 10 10 m 100 V cm Distance = × = μ = Problem 2 (Text 2.27) Silicon is doped with 6 x 10 18 boron atoms/cm 3 . (a) Is this n- or p- type silicon? Since boron is in group III of the periodic table, it is an acceptor 18 3 A N = 6 10 /cm × Assume N D = 0, since it is not specified. Therefore, the material is p-type. ( b) What are the electron and hole concentrations at room temperature? At room temperature, 10 3 10 / cm i n (text page 47) and 18 3 A N = 6 10 /cm i n × Therefore, 18 3 6 10 cm p / × and 2 20 6 3 18 3 10 cm 16.7 cm 6 10 cm i n / n / p / = = × (c) What are the electron and hole concentrations at 200°K? At 200°K, ( 29 ( 29 G 5 1 12 E 3 8 62 10 200 2 3 31 9 6 T T 1 08 10 200 5 28 10 cm . . x k i n B e . x e . / - - - = = = × Therefore, 18 3 6 10 cm p / × and 2 9 6 10 3 18 3 5 28 10 cm 8.80 10 cm 6 10 cm i n . / n / p / - × = = × × Problem 3 (Text 2.30) Silicon is doped with 5 x 10 17 boron atoms/cm 3 and 2 x 10 17 phosphorus atoms/cm

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Sol1 - ECE 255 ELECTRONIC ANALYSIS AND DESIGN Homework 1...

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