TABLE OF CONTENTS A monograph on microwave field effect transistors would be incomplete without an introductory chapter on basic semiconductor theory. Thus, this chapter gives a basic review of energy bands in solids and introduces the reader to the concepts of intrinsic and impurity semiconductors and metal-to-semiconductor contacts.
For many years the energy levels of electrons in solids have been treated in discrete bands separated by gaps in which ordinarily no energy levels occur.
The band structure of occupied energy levels of electrons in solids have been extensively investigated by using X-ray emission spectroscopy. When the crystal structure of the solid is bombarded by high-energy electrons, electrons are ejected from the innermost part of the atom thus allowing transitions to take place between the outer and inner atomic shells. Such transitions give rise to narrow discrete spectroscopic lines, except for certain lines that are broader due to the transition of certain outer electrons which have a range of energies.
In ionic crystals, such as NaCl, there are two energy bands occupied by electrons where one energy band is due to the outer electrons of the positive ion and the other to the outer electrons of the negative ion. In valence-bond crystals, such as diamond, only one energy band exists and this is attributed to the electrons in the valence bond.
The band structure of unoccupied energy levels has been investigated by the use of X-ray absorption spectroscopy. When the crystal is irradiated by X-rays at certain frequencies there...
