Introduction:
Germanium is a semimetal that has properties of both metals and non-metals. It is widely used in electronic devices such as transistors and diodes. Arsenic is a group V element that has five valence electrons.

Effect of adding arsenic to germanium:
When arsenic is added to germanium, it becomes an extrinsic semiconductor. This means that the conductivity of germanium is increased due to the addition of arsenic. This is because arsenic has one more valence electron than germanium, which means that it can donate an extra electron to the germanium lattice.

Extrinsic semiconductor:
An extrinsic semiconductor is a semiconductor material that has been intentionally doped with impurities to increase its conductivity. The impurities are added in small amounts to the semiconductor material to change its electrical properties. Extrinsic semiconductors are also called doped semiconductors.

Types of extrinsic semiconductors:
There are two types of extrinsic semiconductors:

1. N-type extrinsic semiconductor: When an element with extra valence electrons, such as arsenic, is added to a semiconductor material, it becomes an N-type semiconductor. In N-type semiconductors, the extra electrons donated by the impurity atoms become the majority carriers, and the holes become the minority carriers.

2. P-type extrinsic semiconductor: When an element with fewer valence electrons, such as boron, is added to a semiconductor material, it becomes a P-type semiconductor. In P-type semiconductors, the impurity atoms create holes in the valence band, which become the majority carriers, and the electrons become the minority carriers.

Conclusion:
Therefore, the addition of arsenic to germanium makes it an extrinsic semiconductor, specifically an N-type extrinsic semiconductor. This increases its conductivity and makes it more suitable for use in electronic devices.

Extrinsic semiconductor:- Doped semiconductors are called as extrinsic semiconductors
As is a dopant as it adds impurity in Ge
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