Semiconductor is a material whose conductivity lies in-between that of the conductors and the insulators. Semiconductors which are chemically pure, meaning free of impurities, are called Intrinsic Semiconductors or Undoped Semiconductor or i-type Semiconductor. The most common intrinsic semiconductors are Silicon (Si) and Germanium (Ge), which belong to Group IV of the periodic table. The atomic numbers of Si and Ge are 14 and 32, which yields their electronic configuration as 1s²2s²2p⁶3s²3p² and 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p² respectively. This indicates that both Si and Ge have four electrons each in their outer-most i.e. valence shell (indicated by red colour). These electrons are called valence electrons and are responsible for the conduction-properties of the semiconductors.
What is Intrinsic Semiconductor?
Intrinsic semiconductor is a crystal having all atoms of same nature i.e. extremely pure semiconductor is called intrinsic semiconductor.Si atom has four valence electrons. Every Si atom in the crystal shares its four valence electrons with its four neighbours. Thus, all atoms complete their octet and attain stability. At initial temperature i.e. absolute zero temperature (0 Kelvin), the valence band is completely filled with electrons and the conduction band is empty. At room temperature (330 kelvin), the electrons in the valence band are moved to the conduction band. When an electron leaves the valence band it creates a vacancy known as hole. A hole attracts electrons as it is positively charged.In intrinsic semiconductor number of free electrons is equal to number of holes.
ne = nh
When current is passed through a material containing free electrons, the current is conducted and it is known as current due to electrons (Ie).
Similarly, when a current is passed through a material it can be conducted due to holes and it is known as current due to holes (Ih).
The total current passing through intrinsic semiconductors is I = Ie + Ih.