Semiconductors' definition, types, Energy Bands, and Applications

Semiconductors Types, Energy Bands, and Applications.

Is the most, common and wide material used in electronic devices due to its properties and advantages. It is the basic material used in modern technology applications and manufacturing. It is used in computers, communication, military systems, and renewable energy systems.

What is the meaning of energy bands of atoms?

The energy band is the atom’s energy profile which represents the energy levels of carrier charges. It also determines the behavior of the material based on the distribution of the inside charges (carriers). The below figure shows the main types of energy bands.

What are the types of atom’s energy bands?

Valance band. 

It is the energy band that contains valance electrons’ energy levels. It is filled or partially filled with valance electrons and can’t be empty. Its electrons have a weak bond or connection with the atom’s nucleus. This energy band exists under the conduction band energy level. The energy of electrons in the valence band is lower than that of electrons in the conduction band.

Forbidden energy gap.

 It is the energy gap between the valance band and the conduction band. There is no electrons or hole at this energy level. It is also defined as the energy gap that should be passed by electrons when excited by enough energy. the electrical conductivities are defined by the forbidden energy gap as well as the materials' specifications.

Conduction band.

 It is the band that includes the conduction electrons’ energy level. This energy band is empty or partially filled. When the electrons in the valance band are excited by enough energy to pass the forbidden energy gap it will jump to the conduction band and become free electrons. The conduction electron’s energy is higher than the energy of the electrons in the valance band. 

What are the three types of solid materials?

Conductors (metals). 

 In Conductors there is no energy gap (forbidden gap) exists between the valance and conduction band even the conduction band rather, the valance band is overlapped so the conduction electrons move through the lattice easily. In conductors like copper, the conductivity is high and the resistivity is low.

Semiconductor materials. 

It is a material between conductors and insulators. The semiconductors’ forbidden energy gap is considered small which enables electrons in the valance band to jump to the conduction band by a small excitation energy like temperature or sunlight.

Insulators.

In insulators the energy gap between the valance band and conduction band is large and the electrons can’t jump from the valance band to the conduction band because it needs a huge amount of energy to excite the valance electrons to leave the valance band and jump to the conduction band. The insulator materials like glass and ceramic have very low conductivity and very high resistivity.

What is the meaning of the semiconductor materials?

Semiconductor materials are materials between conductors and insulators. In its normal condition (at zero kelvin temperature), it is considered an insulator because it hasn’t any electrons in its conduction band and the electrons in the valance band are forming covalent bonds between each other.

 At certain conditions and specific parameters like temperature increasing or sunlight photovoltaic effect, it turns into a conductor when the electrons are excited and leave their original position and become free to move the entire lattice. Semiconductor materials could be pure (intrinsic) semiconductors or compounds (extrinsic). The purest semiconductor materials are silicon and germanium while the compounds are cadmium selenide and gallium arsenide.

What are the types of semiconductor materials?

Intrinsic semiconductors.

they are materials made chemically from completely pure and free from impurities and single atoms of semiconductors. The number of electrons and holes that are balanced and equal. It depends on the internal characteristics of the material like the effect of temperature, not the external ones (impurities). The below figure shows the pure (intrinsic) semiconductor.

 

The intrinsic semiconductor materials have low electrical conductivity at Standard Test Conditions (STC). In intrinsic semiconductors, the motion of free electrons and holes determines the current flow. The summation of the electrons' current generated by the thermal effect and the holes’ current is the total current of the semiconductor materials.

Extrinsic semiconductors.

they are semiconductor materials made from doped intrinsic materials through a process called the doping process by planting impurities materials. The charge majority, minority, and energy band profiles depend on the type of dopant. The dopant may be of the fifth group then the majority are electrons and the minority are holes. The below figure shows the extrinsic semiconductor materials

The dopant in that case called a donor. If the dopant is of the third group, the majority carriers will be holes and the minority are electrons and the dopant will be called an acceptor. There is no balance between holes and electrons and it depends on the dopant element. The electrical conductivity of the extrinsic semiconductors is high.

Energy bands for Semiconductors and their occupied electrons.

Pure semiconductor materials (intrinsic), have tetravalent electrons (four electrons) in the valance band these four electrons are shared with other atoms and form the covalent bond. The covalent bond in the semiconductors’ lattice is very strong and the semiconductors are considered insulators at zero kelvin temperature. At that condition, no electrons exist in the conduction band and the conductivity is zero. As the temperature increase, some electrons gain energy and become free electron leaving a hole behind in their original position. The electrons that represent the negative charges and the holes that represent the positive charges have the same numbers and magnitudes but different polarities.

What are the properties of the Semiconductors?

• Can be controlled to work as a conductor or insulator as per thermal characteristics, doping. process, and other sources of excitation like sunlight in solar cell.
• As per its electrical properties, it is suitable for amplifiers, switches, and energy conversions.
• Low amount of power losses.
• Low weight and size.
• The flow of current is according to electrons and holes.
• Conductivity: 105 to 10-6 mho/m.
• Resistivity: 10-5 to 106 Ωm.
• Negative Temperature coefficient of resistance.
• High reliability.
• Good compactness.
• low cost.

What are the semiconductor applications?

• Solar cells and solar panels.
• Temperature sensors because its thermal parameters.
• Used in calculators and computers.
• Used in integrated circuit.
• controllers and microcontrollers.
• Diodes thyristors, and transistors.

The below figure shows the semiconductors applications.

As per the chemical and physical characteristics of the semiconductors, it is used widely in industrial processes like space vehicles, microprocessors robots, and trans fabrications. The advanced step of the semiconductor materials is the P-N Junction will be explained later.