Semiconductors have special electrical properties. The substance that conducts electricity is called a conductor and a substance that does not conduct electricity is called an insulator. Semiconductors are substances with properties that lie between the conductor and insulators.
Integrated circuits and electronic discrete components such as Diodes, BJT, FET and MOSFET are made of semiconductors. The Common semiconductors materials are silicon(Si) and germanium(Ge). Silicon is well-known and it is available abundant on earth. Common semiconductor compounds are such as gallium arsenide(GaAs) or indium antimonide. Silicon is used in electronic circuit fabrication and gallium arsenide is used in solar cells, laser diodes, etc.
Semiconductors became very essential for almost all electronic appliances as well as for social infrastructure that supports our everyday life. The Semiconductors (SC) plays an important role in equipment control in a variety of fields such as operating air conditioners at a comfortable temperature, improving automobile safety, laser treatment in medical care facilities and many more.
The advances of semiconductor technology have driven systems efficiency, miniaturization, and energy savings, which help us to preserve the global environment and achieve a safe and comfortable life and create a prosperous future.
Semiconductors were discovered in the 19th century. In the 1940s, transistors were invented. Radios, which used vacuum tubes until then, were downsized and became portable.
A well-known semiconductor is a Silicon. Electronic components using semiconductors are called semiconductor devices, including the IC, which is an integrated circuit (IC) of transistors. Semiconductor devices mounted inside almost all electronics appliances are very important electronic components, that support our everyday life.
Charge Carriers in Semiconductors
Electrons (e) (-ve) and Holes (p) (+ve) are the two types of charge carriers responsible for the flow of current in semiconductors. Holes (valence electrons) are the positively charged carrier whereas electrons are negatively charged carriers. Both electrons and holes are equal in magnitude (1.6x10-19C) but opposite in polarity.
Electrons and Holes mobility
In the semiconductor, the mobility of electrons is far higher than that of the holes mobility. It is due to their different band structures and scattering mechanisms.
Electrons are travel in the conduction band (Ec) whereas holes travel in the valence band (Ev). Whenever an electric field (E) is applied to the semiconductors, holes cannot move as electrons due to their restricted movent.
The jump of electrons from their inner orbit to higher outer orbit results in the creation of holes in semiconductors. Because the holes experience stronger atomic force by the nucleus than the electrons, hence holes have lower mobility also holes have higher rest mass than electrons.
The mobility of a particle in a semiconductor is more if;
- The effective mass of particles is lesser.
- The time between scattering events is more.
Properties of Semiconductors
Semiconductors(SC) can conduct electricity under particular conditions or circumstances. This unique property makes it a superb material to conduct electricity in a controlled manner as needed. Unlike conductors, the charge carriers in semiconductors arise only due to external energy (thermal agitation), Which causes a particular number of valence electrons to cross the energy gap and jump into the conduction band, leaving an equal amount of unoccupied energy states, i.e. holes (+ve). Conduction thanks to electrons and holes are equally important.
- Resistivity: 10-5 to 106 Ωm
- Conductivity: 105 to 10-6 mho/m
- Temperature coefficient of resistance: Negative
- Current Flow: Due to electrons and holes
Important Properties of Semiconductors are
- Pure Semiconductor acts like a perfect insulator at Zero Kelvin. On increasing the temperature, it works as a conductor.
- Due to their exceptional electrical properties, semiconductors (SC) can be modified by doping to make semiconductor devices suitable for energy conversion, switches, and amplifiers.
- Lesser power losses.
- Semiconductors are smaller in size and possess light in weight.
- Their resistivity is higher than conductors but lesser than insulators.
- The resistance of semiconductor materials decreases with the increase in temperature and vice-versa.
Types of Semiconductors
Semiconductors can be classified as:
- Intrinsic Semiconductor
- Extrinsic Semiconductor
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