What are semiconductors?

Answer 1

Semiconductors are insulators at low temperatures and reasonably good conductors at higher temperatures.

semiconductors whose ability to conduct electric lies between those of conductor and insulator

Additional:

Common semiconductors include silicon and germanium, which are tetra-valent, that is each atom has four electrons in its outer orbit. In the normal crystalline form, the atoms form covalent bonds where adjacent atoms share an electron. Electrons thus bound are not free to move and are not affected by an electric field. These bonds are fairly weak, and are easily broken. At any temperature above absolute zero, many of the bonds are broken leaving electrons free to move. So, as temperature increases, the semiconductor material becomes a better and better conductor. This is an intrinsic, or pure semiconductor. So, the above statement " Semiconductors are insulators at low temperatures and reasonably good conductors at higher temperatures." is absolutely true.

As used in electronics, impurities are intentionally introduced (doped) into the semiconductor. When penta-valent (5 outer electrons) elements such as Arsenic and Antimony are used, the semiconductor has many free electrons, and is said to be n-type. If tri-valent (3-outer electrons) elements such as Boron, Gallium and Indium are used, the material is electron starved, and is said to be p-type. If we dope one side of a semiconductor block such that it is n-type, and the other side p-type, a so-called semiconductor junction is formed. This is the building block for all modern electronics such as the diode, transistor and integrated circuit (IC).