What you are expected to learn

At the end of this module, you should be able to:

• Identify materials that act as semiconductors.

• Define covalent bonding.

• Describe the doping process for creating N- and P-type semiconductor materials.

• Explain how doping supports current flow in a semiconductor material.

How to learn from this module

Going through this module can be both a fun and a meaningful learning experience. All you need to do is make use of your time and resources efficiently. To do this, here are some

tips for you:

1. Take time in reading and understanding each lesson. It is better to be slow but sure than to hurry finishing the module only to find out that you missed the concepts you are supposed to learn.

2. Do not jump from one chapter to another. Usually, the lessons are arranged such that one is built upon another, hence an understanding of the first is essential in comprehending the succeeding lessons.

3. Be honest. When answering the test items, do not turn to the key to correction page unless you are done. Likewise, when performing experiments, record only what you have really observed.

4. Safety first. Perform the experiments with extra precaution. Wear safety gears whenever necessary.

5. Don’t hesitate to ask. If you need to clarify something, approach your teacher or any knowledgeable person.

What to do before (Pretest)

Semiconductors are the basic components of electronic equipment. The more commonly used semiconductors are the diode (used to rectify), the transistor (used to amplify), and the integrated circuit (used to switch or amplify). The primary function of semiconductor devices is to control voltage or current for some desired result.

Advantages of semiconductors include the following:

• Small size and weight

• Low power consumption at low voltages

• High efficiency

• Great reliability

• Ability to operate in hazardous environments

• Instant operation when power is applied

• Economic mass production

Disadvantages of semiconductors include:

• Great susceptibility to changes in temperature

• Extra components required for stabilization

• Easily damaged (by exceeding power limits, by reversing polarity of operating voltage, by excess heat when soldering into circuit)

• Semiconductor materials are any materials with characteristics that fall between those of insulators and conductors.

• Pure semiconductor materials are germanium (Ge), silicon (Si), and carbon (C).

• Silicon is used for most semiconductor devices.

• Valence is an indication of an atom’s ability to gain or lose electrons.

• Semiconductor materials have valence shells that are half full.

• Crystals are formed by atoms sharing their valance electrons through covalent bonding.

• Semiconductor materials have a negative temperature coefficient: As the temperature rises, their resistance decreases.

• Heat creates problems with semiconductor materials by allowing electrons to break their covalent bonds.

• Heat energy can break covalent bonds, making free electrons available to conduct current. This gives silicon and other semiconductor materials a negative temperature coefficient.

• As the temperature increases in a semiconductor material, electrons drift from one atom to another.

• A hole represents the absence of an electron in the valence shell.

• Hole current is opposite in direction to electron current.

• A difference of potential, applied to pure semiconductor material, creates a current flow toward the positive terminal and a hole flow toward the negative terminal.

• Semiconductors with free holes are classified as P-type materials.

• Current flow in semiconductor materials consists of both electron flow and hole movement.

• Doping is the process of adding impurities to a semiconductor material.

• Doping a semiconductor crystal changes its electrical characteristics.

• Pentavalent materials have atoms with five valence electrons and are used to make N type material.

• Trivalent materials have atoms with three valence electrons and are used to make P type material.

• In N-type material, electrons are the majority carrier and holes are the minority carrier.

• In P-type material, holes are the majority carrier and electrons are the minority carrier.

• N- and P-type semiconductor materials have a higher conductivity than pure semiconductor materials.

• To move a valence electron to the conduction band, an amount of energy equal to or greater than the band gap must be applied.

Self Check