“SEMICONDUCTORS”

OBJECTIVES

1.Identify the importance of semiconductors.

2.Differentiate semicondutors from conductors and insulators.

3. Identfiy and describe the elements that works as semiconductors.4.Appreciate the importance of

semicondutors to modern technology.

VACUUM TUBES

Vacuum tube is considered as the backbone of electronic equipment.

WHAT IS a VACUUM TUBE ???!

VACUUM TUBE

In electronics, a vacuum tube, electron tube (in North America), thermionic valve, tube, or valve is a device controlling electric current through a vacuum in a sealed container. The container is often thin transparent glass in a roughly cylindrical shape.

VACUUM TUBE

The simplest vacuum tube, the diode, is essentially an incandescent light bulb with an extra electrode inside. 

Vacuum tubes are thus used for rectification, amplification, switching, or similar processing or creation of electrical signals.

WHAT IS A SEMICONDUCTOR?

A semiconductor is a material which has electrical conductivity between that of a conductor such as copper and an insulator such as glass. The conductivity of a semiconductor increases with increasing temperature, behaviour opposite to that of a metal

Current conduction in a semiconductor occurs via free electrons and "holes", collectively known as charge carriers. Adding impurity atoms to a semiconducting material, known as "doping", greatly increases the number of charge carriers within it.

When a doped semiconductor contains excess holes it is called "p-type", and when it contains excess free electrons it is known as "n-type".

DOPING

The semiconductor material used in devices is doped under highly controlled conditions to precisely control the location and concentration of p- and n-type dopants. A single semiconductor crystal can have multiple p- and n-type regions; the p-n junctions between these regions have many useful electronic properties.

SEMICONDUCTORS

Semiconductors are the foundation of modern electronics, including radio, computers, and telephones.

Semiconductor-based electronic components include transistors, solar cells, many kinds of diodes including the light-emitting diode (LED), the silicon controlled rectifier, photo-diodes, and digital and analog integrated circuits.

Increasing understanding of semiconductor materials and fabrication processes has made possible continuing increases in the complexity and speed of semiconductor devices, an effect known as Moore's Law

SEMICONDUCTOR MATERIALS

Semiconductor materials are nominally small band gap insulators. The defining property of a semiconductor material is that it can be doped with impurities that alter its electronic properties in a controllable way

Most commonly used semiconductor materials are crystalline inorganic solids. These materials are classified according to the periodic table groups of their constituent atoms.

Materials

A large number of elements and compounds have semiconducting properties, including:

• Certain pure elements found in Group IV of the periodic table; the most commercially important of these elements are silicon andgermanium.

• Binary compounds, particularly between elements in Groups III and V, such as gallium arsenide, Groups II and VI, groups IV and VI, and between different group IV elements, e.g. silicon carbide.

• Certain ternary compounds, oxides and alloys.

• A number of organic compounds.

An intrinsic semiconductor is made up of one pure element or pure compound. At room temperature, the conductivity of intrinsic semiconductors is relatively low because there are very few charge carriers available.

Conductivity is greatly enhanced by a process called doping, in which very small amounts of other elements are added to the intrinsic crystal to create what is called an extrinsic semiconductor.

Most common semiconducting materials are crystalline solids, but amorphous and liquid semiconductors are also known. These include hydrogenated amorphous silicon and mixtures of arsenic, selenium and tellurium in a variety of proportions.