Question

(3) The color of extrinsic semiconductor will tend to be blue or red, relative to intrinsic semiconductor?

Answer 1

Intrinsic semiconductors:

These are pure semiconducting materials and no impurity atoms are added to them.

For example: The crystals of pure elements like germanium and silicon are considered as Intrinsic Semiconductors.

Properties:

1. In intrinsic semiconductor, the number density of electrons is equal to the number density of holes. i.e. ne=nh
2. The electrical conductivity is low
3. The electrical conductivity of intrinsic semiconductors depends on their temperatures

Extrinsic semiconductors:

When some impurity is added to an intrinsic semiconductor, extrinsic semiconductors can be produced.

Properties:

1. In extrinsic semiconductor, the number density of electrons is not equal to the number density of holes. i.e. ne?nh
2. The electrical conductivity is high
3. The electrical conductivity depends on the temperature and the amount of impurity added in them

Doping:

Doping is the process of adding impurities to intrinsic semiconductors to change their properties. As we know Silicon and Germanium are known as intrinsic semiconductors. Mostly Trivalent and Pentavalent elements are used to dope these elements.

When an intrinsic semiconductor is doped with Trivalent impurity, it becomes a P-Type semiconductor. The P stands for Positive, which means the semiconductor is rich in holes or positively charged ions.

When we dope intrinsic materials with Pentavalent impurities we get N-Type semiconductors, where N stands for Negative. N-type semiconductors have negatively charged ions or, in other words, they have excess electrons.

So in extrinsic semiconductors holes/electrons are present in their structure . So they can absorb perticular wavelenth of light and emt correspnding color.but in intrinsic semiconductors number of holes and elecrons are eual and pure semiconductors.thats the reason why extrinsic semiconductor will tend to be blue or red relative to intrinsic semiconductor