Intrinsic Semiconductor
A semiconductor in its extremely pure form is called intrinsic semiconductor.
Pure Ge and Si are intrinsic semiconductor. Semiconductor materials belongs to fourth group of periodic table. Their electrical behavior extremely depends upon its purity. The semiconductor elements have four valance electrons. In crystalline solids, the atoms of these elements arrange themselves in such a pattern that each atom has four equidistant neighbors. Pure Ge and Si are intrinsic semiconductor. Semiconductor materials belongs to fourth group of periodic table. Their electrical behavior extremely depends upon its purity. The semiconductor elements have four valance electrons. In crystalline solids, the atoms of these elements arrange themselves in such a pattern that each atom has four equidistant neighbors.
Extrinsic Semiconductor
An impure form of semiconductor material is called extrinsic semiconductor.
By adding impurity the conductivity of the semiconductor increases. Pure Ge and Si are intrinsic semiconductor. Semiconductor materials belongs to fourth group of periodic table. Their electrical behavior extremely depends upon its purity. The semiconductor elements have four valance electrons. In crystalline solids, the atoms of these elements arrange themselves in such a pattern that each atom has four equidistant neighbors.
Doping
The process of adding the small impurity atom in a pure semiconductor by a controlled way is called doping and the impurity material itself is called dopant.
The impurity atoms are added in a semiconductor in the ratio of 1 to 10^6.
Types of Extrinsic Semiconductors
These are two types of extrinsic semiconductors:
- N-type Semiconductor
- P-type Semiconductor
1. N-type Semiconductors
The semiconductor which is formed by adding pentavalent impurity to a pure semiconductor is called N-type semiconductor.
An atom belonging to fifth group such a antimony, phosphorus or arsenic has five valance electrons. When it is added to Germanium Ge or Silicon Si having four electors in four electrons in their outer most orbit then four valance electrons of pentavalent element like phosphorous form covalent bonds with four neighboring Si atoms, while the fifth valence electron provides a free electron in the crystals. An atom belonging to fifth group such a antimony, phosphorus or arsenic has five valance electrons. When it is added to Germanium Ge or Silicon Si having four electors in four electrons in their outer most orbit then four valance electrons of pentavalent element like phosphorous form covalent bonds with four neighboring Si atoms, while the fifth valence electron provides a free electron in the crystals.
2. P-type Semiconductors
The semiconductor which is formed by adding trivalent impurity to a pure semiconductor is called p-type semiconductor.
An atom belonging to third group such as aluminum , boron , gallium or indium has three valance electrons. An atom belonging to fifth group such a antimony, phosphorus or arsenic has five valance electrons. When it is added to Germanium Ge or Silicon Si having four electors in four electrons in their outer most orbit then four valance electrons of pentavalent element like phosphorous form covalent bonds with four neighboring Si atoms, while the fifth valence electron provides a free electron in the crystals. Since trivalent impurity accept a free electron, so it is called accepter impurity. An atom belonging to third group such as aluminum , boron , gallium or indium has three valance electrons. An atom belonging to fifth group such a antimony, phosphorus or arsenic has five valance electrons. When it is added to Germanium Ge or Silicon Si having four electors in four electrons in their outer most orbit then four valance electrons of pentavalent element like phosphorous form covalent bonds with four neighboring Si atoms, while the fifth valence electron provides a free electron in the crystals. Since trivalent impurity accept a free electron, so it is called accepter impurity.
