TABLE OF CONTENTS This chapter reviews some of the basics of semiconductor theory that are necessary for an understanding of the development of the device models which follows. Also reviewed is pn junction theory as its behavior is basic to the operation of transistors. The review is brief and covers only those topics which have direct relevance to MOS VLSI circuits. For more exhaustive treatments, the reader is referred to textbooks on the subject [1] [12].
The starting material in the fabrication of MOS devices and integrated circuits (IC) is silicon in the crystalline form. The silicon wafers are cut parallel to either the ?111 ? or ?100 ? planes with ?100 ? material being the most commonly used. This is largely due to the fact that ?100 ? wafers, during processing, produce the lowest charges at the oxide-silicon interface and higher mobility [13]. Polycrystalline silicon (polysilicon) is also extensively used in IC technology as a conductor, contacts or gate in MOS devices [14]. This material is structurally more complex than single crystal silicon. It consists of many small regions, each having well defined structure but differing from its neighboring regions. For circuit model purposes we can treat polycrystalline silicon as being crystalline in nature.
In a silicon crystal each atom has four valence electrons to share with its four nearest neighboring atoms. The valence electrons are shared in a paired configuration called a covalent bond. It is predicted by...
