Introduction to Semiconductors PDF

INTRODUCTION TO SEMICONDUCTORS ECEN2012: Basic Electronics (Lecture) OBJECTIVES Describe the structure of an atom Discuss insulators, conductors, and semiconductors and how they differ Describe how current is produced in a semiconductor Describe the properties of n-type and p-type semico...

INTRODUCTION TO SEMICONDUCTORS ECEN2012: Basic Electronics (Lecture) OBJECTIVES Describe the structure of an atom Discuss insulators, conductors, and semiconductors and how they differ Describe how current is produced in a semiconductor Describe the properties of n-type and p-type semiconductors Describe how a pn junction is formed THE ATOM Neutron – neutrally charged particle Proton – positively charged particle Electron –negatively charged particle Free electrons – electrons that have left their orbit in an atom and are wandering freely through the materials - Its directional movement makes an electric current ATOMIC MASS AND NUMBER The mass of proton is 1836 times the mass of the electrons The atomic number represents the number of protons. 10^-10 m*Angstrom = 0.01 nm  Atomic structure of (a) silicon; (b) germanium; and (c) gallium and Tetravalent arsenic. Trivalent Pentavalent VALENCE is used to indicate that the potential (ionization potential) required to remove any one of these electrons from the atomic structure is significantly lower than that required for any other electron in the structure. For materials in electronics, valence electrons decide whether something is a conductor (lets electricity flow), insulator (blocks electricity), or semiconductor (in between). IONIZATION Process where atoms lose or gain electrons. Anions Cations CONDUCTOR, INSULATOR, AND SEMICONDUCTOR Conductor – materials with less than four valence electrons. It allows electrical current to flow easily because of more free electrons. Example: copper (Cu), silver (Ag), gold (Au), and aluminum (Al) Insulator – materials with more than four electrons. It will not allow the flow of current because there are less or no free electrons. Example: rubber, plastics, glass, mica, and quartz. Semiconductor – materials with exactly four valence electrons. It has electrical characteristics between conductor and insulator. Example: antimony (Sb), arsenic (As), astatine (At), boron (B), polonium (Po), tellurium (Te), silicon (Si), and germanium (Ge) ATOMIC BONDING Ionic Bonding – results from attractive forces between positive and negative ions or between pairs of oppositely charged ions. – transfer! – metals and nonmetals. ATOMIC BONDING Covalent Bonding – results when atoms share their valence electrons with other atoms – shared, holds them together. – nonmetals and nonmetals. ATOMIC BONDING Metallic Bonding – results from attractive forces between a group of positive ions and sea of electrons that are free to move about among its ion. CONDUCTION IN SEMICONDUCTORS Electron Flow Hole Flow TYPES OF SEMICONDUCTOR MATERIALS Intrinsic Materials Extrinsic Materials The process of adding impurities is known as “doping”. TYPES OF EXTRINSIC MATERIALS N –type – adding donor impurities, such as pentavalent atoms. P – type – adding acceptor impurities, such as trivalent atoms. TYPES OF DOPANT Donor / Pentavalent Atoms (Group 5A) Phosphorus, Arsenic, Antimony, Bismuth Acceptor / Trivalent Atoms (Group 3A) Boron, Indium, Gallium, Aluminum  A semiconductor in its pure (intrinsic) state is neither a good conductor nor a good insulator. Compound semiconductors such as gallium arsenide, indium phosphide, gallium nitride, silicon carbide, and silicon germanium are also commonly used. The single-element semiconductors are characterized by atoms with four valence electrons. Silicon is the most commonly used semiconductor. Electron and Hole Current Majority and Minority Carriers In an n-type the electron is called the majority carrier and the hole the minority carrier. In a p-type material the hole is the majority carrier and the electron is the minority carrier.