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1.1_Introduction - Introduction Abstract This note serves...

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Introduction June 22, 2014 Abstract This note serves as an introduction of both n -type and p -type semi- conductors. For more details, please refer to the reference books or more online materials. 1 Materials In terms of their electrical properties, materials can be classified into 3 groups: Insulator : a material that does not conduct electrical current under nor- mal conditions. For examples, rubber, plastics, glass, etc. Conductor : a material that easily conduct electrical current. For exam- ples, copper, gold, silver, etc. Semiconductor : a material with characteristics fall between insulator and conductor. A semiconductor in its pure state is neither a good con- ductor nor a good insulator. For examples, silicon (Si), germanium (Ge), boron (B), arsenic (As), antimony (Sb), etc. These materials have atomic structures which may be easily altered to obtain specific elecrical characteristics. 1.1 Semiconductive Atom All atoms have a nucleus where protons and neutrons are located. It carries positive charges, which are surrounded by electrons orbiting in certain shells around the nucleus, as shown in Figure 1. 1
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Figure 1: Atomic Structure The maximum number of electrons ( N e ) that can exist in each shell of an atom is a fact of nature and can be calculated by the formula N e = 2 n 2 where n indicates the number of the shell. For example, the 1st shell (i.e., n = 1) can only hold 2 electrons, the 2nd shell (i.e., n = 2) can hold 8 electrons, the 3rd shell can hold 18 electrons and so on. The outermost shell of an atom is called the valence shell
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