L38 - SUMMARY FROM LAST CLASS Semiconductor devices The...

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Dr. P. Lucas U of A MSE 110 Semiconductor devices SUMMARY FROM LAST CLASS The Hall effect is based on the Lorentz force whereby a magnetic field B exerts a force on a moving charged particle. In P-type semiconductors, deflected holes create a positive voltage V H while in N-type semiconductors, deflected electrons generate a negative V H . A diode allows current to flow only in one direction. The Fermi level is the energy level which has a probability of occupancy of ½. Due to different concentrations of holes and electrons, the Fermi level is higher in the N-type and lower in the P-type. In the depletion layer at the p-n junction, there is no charge carriers as electrons and holes recombine to form positive and negative dopant ions and build up a space charge. The space charge shifts and equalizes the Fermi energy on both sides. In forward bias, many electrons on the N side and holes on the N side are available to flow through the junction while in reverse bias no electrons and holes are available and no current can flow.
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Dr. P. Lucas U of A MSE 110 Modern synthetic materials POLYMERS Actually 2500 years ago Amazonian Indians used Hevea tree sap to make latex boots, a naturally occurring polymer. The problem is that they would oxidize and only last a day before falling apart. In 1839, Mr Goodyear decides for no particular reason to cook latex with sulfur and produces what is still known and widely used as rubber. However, at the time nobody knew that rubber was actually a polymer. It was not before the middle of the 20 th century that the concept of long chain molecules constituting polymers was recognized and the first artificial polymers were synthesized.
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Dr. P. Lucas U of A MSE 110
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This note was uploaded on 11/19/2009 for the course MSE 110 taught by Professor Lucas during the Spring '08 term at University of Arizona- Tucson.

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L38 - SUMMARY FROM LAST CLASS Semiconductor devices The...

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