文档介绍：Unit 1 Introduction to Semiconductors
Part I
Semiconductors are materials that exhibit properties that are between a metal and a non-metal. Their electrical properties are part way between a conductor and an insulator—thus they are called "semiconductors". (Actually they are much closer to insulators than conductors.) A number of materials have these properties:
The crystalline forms of most elements of Group IV (valency 4) (silicon⑴，germanium, tin).
Some forms of specific elements一boron (Group III), arsenic and antimony (Group V), selenium and tellurium (Group VI).
Crystalline alloys of elements in Group III (valency 3) with elements of group V (valency 5). Gallium arsenide (a compound or alloy of gallium and arsenic) is a good example here.
Some compounds of elements of Group VI with elements of Group II.
Probably the most versatile elements are those with four electrons in their outer shell (Group IV: carbon, silicon, germanium, tin, lead). Because of the fact that they can have four bonds to four other elements, covalent compounds of endless complexity can be formed. (Indeed DNA is a single carbon-based molecule.)
All of these elements can exist in multiple physical forms. Carbon can take many forms such as graphite (a form a bit like a classical metal) which conducts electricity very well or diamond (a crystalline form) which is an insulator.
Almost anyone who has ever soldered an electrical connection knows the difference between a good soldered joint (where the metal solidifies in a polymorphic form) and a "dry joint" where the solder crystallizes.[2] Polymorphic solder is a very good electrical conductor. Solder (an alloy of lead and tin) in its crystalline form is a semiconductor!
In fact carbon is not classified by chemists as a semiconductor even though diamond does semiconduct at relatively high temperatures (well above room temperature). The technical reason is that carbon has very strong molecular bonds which do not break down very easily (th