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Lab2-ElecConductivityF06-1

# Lab2-ElecConductivityF06-1 - MatE 215 Lab 2 Electrical...

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Unformatted text preview: MatE 215 Lab 2: Electrical Conductivity (Fall 06) Page 1 of 13 Laboratory 2 Electrical Conductivity: The Effect of Heat on Metals and Semiconductors Goal: To understand how heat and atomic bonding interact to control the material’s electrical conductivity with changes in temperature. Learning Objectives: 1. Explain the relationship between a light-emitting diode’s color and the size of its band gap. 2. Use measurements of resistance to determine the band gap (E gap ) of a semiconductor over a range of temperatures. 3. Use measurements of resistance to determine the temperature coefficient of resistivity ( α ) for metals over a range of temperatures. 4. List and then explain the trend of the resistivity vs. temperature for a semiconductor and a metal. 5. Draw a best-fit line to experimental data, approximate its slope, and use it in calculations. MatE 215 Lab 2: Electrical Conductivity (Fall 06) Page 2 of 13 Why Know About Electrical Conduction In Semiconductors? Unless you’ve been living under a rock for the last 25 years, you’ve probably noticed that you are surrounded by gadgets that rely on semiconductors to function. Of course, an electrical device like an integrated circuit (IC) “chip” enlists the help of metals and insulators, but it is the unique conduction properties of semiconductors that allow an IC to function. We can change the electrical conductivity of a semiconductor from “insulator-like” to “conductor-like” by adding a very small amount of another element to the semiconductor (about 1 atom per every billion semiconductor atoms). This process of adding impurities to change the conductivity is called doping . Where Does Electrical Conduction Come From? If you could shrink down to the size of an atom, you would see that electrical conduction is nothing more than the flow of different charges: electrons, which have a negative charge; and sometimes holes, which have a positive charge. You can imagine that a material’s ability to conduct charge – its conductivity – depends on how many charge carriers are available and how easy it is for those charges to move through the material. If you likened the flow of electrical current to the flow of traffic through a city, you might say that the flow of traffic depended on how many vehicles were on the road and the size and quality of the roads. In an equation form, (1) Material type n (1/cm 3 ) μ (cm 2 /V s) metals ~ 10 26 ~ 0.1 semiconductors ~ 10 15-10 21 ~ 10 3 Flow of electrons Number of mobile electrons (or holes) available Ability of electrons (holes) to move about σ conductivity ∝ × n concentration of free carriers × ∝ μ mobility of the free carriers Flow of traffic Number of vehicles on the road Size and quality of the roads MatE 215 Lab 2: Electrical Conductivity (Fall 06) Page 3 of 13 Why Are Semiconductors Different Than Metals?...
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Lab2-ElecConductivityF06-1 - MatE 215 Lab 2 Electrical...

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