Engineering Sciences 154
Valuable references at Links to Electronics Tutorials in particular the list of interactive applets from SUNY-Buffalo.
We shall also make use of the lectures Principles of Semiconductor Devices from the University of Colorado.
Stephen Gray (1666-1736) demonstrates that the static charges of electricity can be conducted by some materials."Between 1729 and 1736 he (Stephen Gray) gave the results of many experiments which showed that the electric virtue of a tube of glass, that had been excited by friction, could be conveyed to other bodies thereby giving them the ability to attract and repel light bodies. Gray and a friend, Jean Desaguliers, conducted experiments which showed that objects such as cork, as far as eight or nine hundred feet away, could be electrified by connecting them to the glass tube with wires or hempen string. They found material such as silk would not convey electricity. They discovered distant objects could not be electrified if the transmission line made contact with earth. The line for transmission was suspended by silk threads to prevent contact with the ground. It was found that metal objects held in the hand and rubbed showed no signs of electrification. However, when mounted on a non-conductor, they became electrified. Gray realized that somehow the earth was responsible for conducting electrical charge away from the body. After this realization Gray found he could electrify any material on earth by friction. He even went as far as to suspend pupils of the house by cords and electrified them, sometimes even drawing sparks from the human body."So Gray is credited with finding that electrical conductors must be insulated and that insulators were not conductors and that a charge could be induced in a previously non-electrified body. He established electricity as a current showing it would travel over a conductor. Gray found water to be a conductor which rendered insulators into conductors when their surfaces were wetted. This concept helps us to understand the rapid loss of charges on humid days by electrified bodies. He sent many of his papers to the Royal Society and was elected a fellow. He continued his research until upon his death bed he tried to describe to his doctor the work he still needed to complete." (source)See also Shocking communications
Fluid model of electricity (see Right, Truth, Authority)"When rubbed with fur, amber acquires resinous electricity; glass, however, when rubbed with silk, acquires vitreous electricity. Electricity repels the same kind and attracts the opposite kind of electricity. Scientists thought that the friction actually created the electricity (their word for charge). They did not realize that an equal amount of opposite electricity remained on the fur or silk.
"In 1747, Benjamin Franklin in America and William Watson (1715-87) in England independently reached the same conclusion: all materials possess a single kind of electrical "fluid" that can penetrate matter freely but that can be neither created nor destroyed. The action of rubbing merely transfers the fluid from one body to another, electrifying both. Franklin and Watson originated the principle of conservation of charge: the total quantity of electricity in an insulated system is constant.
"Franklin defined the fluid, which corresponded to vitreous electricity, as positive and the lack of fluid as negative. Therefore, according to Franklin, the direction of flow was from positive to negative--the opposite of what is now known to be true. A subsequent two-fluid theory was developed, according to which samples of the same type attract, whereas those of opposite types repel." (source)
In 1827 what is now known as Ohm's law appeared in Die galvanische Kette, mathematisch bearbeitet. Between 1825-27, Georg Simon Ohm (1789-1854), professor of mathematics at the Jesuit College of Cologne, had been studying electrical conduction following as a model Fourier's study of heat conduction. Ohm's Law states that the strength of an unvarying electric current is directly proportional to the electromotive force, and inversely proportional to the resistance of the circuit concerned. Need it be said, the unit of resistance is named after him. (source)
The Drude model of electrical conductivity assumes little about the atomistic details of charge carriers. See the separate Drude Model Page. However, the "bottom line" is that if we have both positive ("p") and negative ("n") charge carriers the electrical conductivity is given by:
Data on metallic conductivityThere is, however, a fundamental mystery that emerges from Drude analysis. In particular, the "mean free path" found using the Drude formulas and experimental conductivities is much, much greater than the interatomic distances in metals! Only quantum mechanical ideas can satisfactory resolve (or at least rationalize) the mystery.
AMM data table
The essentially linear temperature dependence of the electrical conductivity of sodium is the hallmark of the metallic conductivity.
We summarize two fundamental notions in our page entitled Quantum Ideas - Atoms and the Periodic Table.
Electronic structure of Group IV atoms:Electrical Characteristics of Group IV elements
Considerations of energy level filling lead us directly to the concept of the covalent bond.
To understand the electrical properties of Group IV elements we must try to understand three fundamental sets of ideas:
- What do we mean by "allowed" and "forbidden energies" or equivalently what is an "energy (band) gap." See our page entitled Energy (Band) Gap.
- What are the charge carrier and how are they excited? See our page entitled Mechanisms of Charge Carrier Generation.
- What is the Fermi Eergy (Level) and what does it tell us about impurity levels? See our page entitled The Fermi Level or Energy: Semiconductor Energetics and Statistics which extensively uses the SUNY-Buffalo applets.
Diode Current/Voltage Characteristic - Real and Idealized
See our page entitled The Physics of pn Junctions which, again, extensively uses the SUNY-Buffalo applets.
See also from L.C.G. Lesurf's The Scot's Guide to Electronics
The Diode: shows an animation of carrier flow across the junction.
The Diode I/V behavior
Diode Fabrication - Our first discussion of device fabrication concepts and technologiesSee our page entitled Diode Current/Voltage Characteristics
See our notes on materials preparation and crystal growthDiode Applications
PN Junction Diode : a wonderful multimedia presentation of the fabrication steps necessary to obtain a planar pn junction diode.
The Semiconductor Manufacturing Process (ppt) (local copy) - is also quite helpful.
See supplementary notes on the use of the load line concept in analyzing diode circuits
See supplementary notes on Diode Applications.
A Primer on Photodiode Technology
Some simulations of Simple Diode Circuits
Wenzel Associates -Time and Frequency Articles