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ECE474S09_Lecture28 - ECE 474 Principles of Electronic...

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ECE 474: Principles of Electronic Devices Prof. Virginia Ayres Electrical & Computer Engineering Michigan State University [email protected]
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Lecture 28: Chp. 04: Current State-of-Art Transistors Photo-generated carriers Find α r for “low level injection” Excess carriers Diffusion and Drift Current Einstein’s relation Find built-in E(x) and n(x)
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Lecture 28: Chp. 04: Current State-of-Art Transistors Photo-generated carriers Find α r for “low level injection” Excess carriers Diffusion and Drift Current Einstein’s relation Find built-in E(x) and n(x)
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Example in Lecture 25: Try to evaluate the constant of proportionality for recombination The constant of proportionality for recombination is α r . (p. 125) Doped Si @ 300K: 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: τ n = τ p = 1 μ sec. n = 101 x 10 17 cm -3 => increase factor: 10 2 p 100 x 10 17 cm -3 => increase factor: 10 16 δ n = g op τ n = (10 25 cm -3 s -1 )(1 x 10 -6 s) = 100 x 10 17 cm -3 δ p = g op τ n = 100 x 10 17 cm -3
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How well did my example problem meet this criteria? Badly.
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Now we will consider the problem from a couple of different angles: Effect of recombination.
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