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# HW3 - EE2 Problem Set#3 Solutions Question 1(10 points...

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EE2 Problem Set#3 Solutions Question 1 (10 points): Given the mobility of electrons as 1200 cm 2 /V-s, determine the resistivity of a n-type silicon with 10 16 cm -3 donor atoms. If the electron effective mass is 0.26m o , calculate the average scattering time (mean free time) for an electron. Mobility of electrons, μ n = 1200 cm 2 /V-sec = 0.12 m 2 /V-sec Given concentration of electrons, n = 10 16 cm -3 Resistivity, ρ = (qnμ n + qpμ p ) -1 For n-type Si, p << n, Therefore, ρ = (qnμ n ) -1 = (1.6 x 10 -19 x 10 16 x 1200) -1 = 0.52 Ω -cm Effective mass, m c * = 0.26m 0 Average scattering time, m m c * n q 0.26 9.1 10 31 0.12 1.6 10 19 1.775 10 13 sec 0.1775 psec Question 2 (10 points): How far is the Fermi level from the valence band for a silicon if the doping is 2x10 17 1/cm 3 of Boron? How far is the Fermi level from the conduction band, assuming the bandgap of silicon is 1.1 eV? You can use equation 3.11 from the book to find the difference between E F and E V .

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