Introduction Chapter 1 : basic electronics

INTRODUCTION

An electronic device controls the movement of electrons. The Study of electronic devices requires a basic understanding of the relationship between electrons and the other components of an atom. The movement of electrons within a solid and the  bonding forces  between atoms  can then be investigated . this leads to a knowledge of the differences between conductors , insulators and semiconductors and to an understanding   of p-Type and n-Type semiconductor materials. Junctions of p-Type and n-Type material (pn- junction) are basic to all but a very  few semiconductors devices . forces  act upon electrons that are adjacent to a pn – Junction , and these forces are altered by the presence of an external bias voltage.

1-1   ATOMIC THEORY

THE ATOM

The Atom can be thought of as consisting of a central nucleus surrounded by orbiting electrons . It may be  compared to a planet with orbiting satellites. Just  are satellites are held in orbit by the attractive force of gravity due to the mass of the planet so each electrons is held in orbit by an electrostatic force of attraction between it and the nucleus.

Each electron has a negative electrical charge of  1.602*10(-19) Coulombs ©.  And  Some particles within the nucleus have a positive charge of the same magnitude. Because opposite charge attract, a force of attraction exists  between the oppositely charged electron and nucleus . Compared to the mass of the nucleus , electrons are relatively tiny particles of almost negligible mass .   In fact they can be considered to be little particles of negative having no mass at all.

The nucleus of an atom is largely a cluster of two types of particles protons, and neutrons. Protons  have a positive electrical charge , equal in magnitude (But opposite in polarity) to the negative charge on an electron . A neutron has no charge at all. Protons and neutrons each have masses about 1800 times the mass of an electron . for a given atom,the number of protons in the nucleus normally  equals the number of orbiting electrons.

Because the protons and orbital electrons are equal in number and equal  and opposite in charge , they neutralize eah other electrically . For this reason , ll atoms are normally electrically neutral. If an atom loses an electron , It has lost some negative charge. Consequently, it becomes positively charged and is referred to as a positive ion. Similarly if an atom gains an additional electron, it becomes negatively charged and is termed a negative ion.

The number of protons in an atom is referred to as atomic number of the atom. The atomic weight is approximately equal to the total number of protons and neutrons in the nucleus of the atom . The atom of the semiconductor material silicon has the 14 protons and 14 neutrons in its nucleus , as well as 14 orbital electrons. Therefore the atomic number for silicon is 14 and its atomic weight is approximately 28.