28_Part2_CHM115_Spring_09

28_Part2_CHM115_Spring_09 - CHM 11500 Lecture 27 Reading...

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CHM 11500 CHM 11500 Lecture 27 Lecture 27
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Reading Interchapter: The Chemistry of Modern Materials, Pages 643-655
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3 Solar Cells (Photovoltaics) Overview of how they work…. To understand how solar cells work, we must understand “n” and “p” type semiconductors at the “band” level.
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4 Question #1 - solo From your reading… Which of the following is true? A. Electrons can freely conduct electricity in a solid as long as the solid has a regular crystal lattice. B. Insulators, metals and semiconductors are distinguished by their crystal lattice structure. C. Semiconductors consist of material that is p-type on one side and n-type on the other, where electrons can move across the junction. D. The energy levels of the individual atoms in the solid combine and form continuous bands (rather than separate orbitals).
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5 Extrinsic and Intrinsic Semiconductors Intrinsic semiconductors – the pure, crystalline material has semiconducting properties (such as pure Si or Ge) Extrinsic semiconductors – The material is “doped” with a small amount of impurity of a similar material (about 1 in 10 6 to 1 in 10 8 atoms)
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6 Doped Semiconductors • Decreased E g (band gap) relative to intrinsic material p-type : Doped with an element with fewer electrons. Provides positive charge carriers (“holes”). n-type : Doped with element with more electrons. Provides negative charge carriers (electrons).
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7 Extrinsic and Intrinsic Semiconductors A. Intrinsic silicon (group IV element). B. Silicon doped with P atoms (group V).
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This note was uploaded on 02/06/2012 for the course CHM 115 taught by Professor Towns during the Spring '08 term at Purdue.

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28_Part2_CHM115_Spring_09 - CHM 11500 Lecture 27 Reading...

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