ECE474S09_Lecture25 - ECE 474: Principles of Electronic...

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ECE 474: Principles of Electronic Devices Prof. Virginia Ayres Electrical & Computer Engineering Michigan State University ayresv@msu.edu
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Chp. 04: Current State-of-Art Transistors Photo-generated carriers Examples Lecture 25: Introduction of Diffusion Current
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Continue Example Problem on RHS: Doped Si @ 300K: N d = 10 17 cm -3 P atoms Fully ionised: N d = N d + Therefore: Majority carrier concentration: n 0 = 10 17 cm -3 Minority carrier concentration: p 0 = 2.25 x 10 3 cm -3 Doped Si @ 300K + laser light: Given: 10 17 cm -3 e- hole pairs (EHPs) are generated every microsecond by laser light on the n-doped Si. τ n = τ p = 1 μ sec. Find the increases in the e- and hole concentrations, δ n and δ p and compare the new concentration values for n and p to the original values for n 0 and p 0 .
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Doped Si @ 300K + laser light Given: 10 17 cm -3 e- hole pairs (EHPs) are generated every microsecond Given: τ n = τ p = 1 μ sec. Find first: the increases in the e- and hole concentrations δ n and δ p: g optical = 10 17 cm -3 EHP 10 -6 sec = 10 25 cm -3 s -1 δ n = g op τ n = (10 25 cm -3 s -1 )(1 x 10 -6 s) = 10 19 cm -3 = 100 x 10 17 cm -3 δ p = g op τ p = 100 x 10 17 cm -3 Doped Si @ 300K: N d = 10 17 cm -3 P atoms Fully ionised: N d = N d + Therefore: Majority carrier concentration: n 0 = 10 17 cm -3 Minority carrier concentration: p 0 = 2.25 x 10 3 cm -3
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Given: 10 17 cm -3 e- hole pairs (EHPs) are generated every microsecond Given: τ n = τ p = 1 μ sec. Find first: the increases in the e- and hole concentrations δ n and δ p: g optical = 10 17 cm -3 EHP 10 -6 sec = 10 23 cm -3 s -1 δ n = g op τ n = (10 25 cm -3 s -1 )(1 x 10 -6 s) = 10 19 cm -3 = 100 x 10 17 cm -3 δ p = g op τ n = 100 x 10 17 cm -3 Doped Si @ 300K: N d = 10 17 cm -3
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ECE474S09_Lecture25 - ECE 474: Principles of Electronic...

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