Question

Write any two points of difference between intrinsic and extrinsic semiconductors.

Hint:

To easily remember: "Intrinsic" means "In its pure state." "Extrinsic" means something "Extra" (impurity) has been added to increase conductivity.

Answer 1

Concept:
• Semiconductors are materials with electrical conductivity between that of a conductor and an insulator.
• They are broadly classified into two categories based on their purity: intrinsic (pure) and extrinsic (doped).

Step 1: Point of Difference 1: Purity and Composition
Intrinsic Semiconductors: These are pure semiconductor materials (like pure Silicon or Germanium) without any significant dopant atoms present. Extrinsic Semiconductors: These are impure semiconductors formed by deliberately adding (doping) a small, controlled amount of trivalent or pentavalent impurity atoms to a pure semiconductor.

Step 2: Point of Difference 2: Charge Carrier Concentration
Intrinsic Semiconductors: The number of thermally generated electrons ($n_e$) in the conduction band is exactly equal to the number of holes ($n_h$) in the valence band ($n_e = n_h = n_i$). Extrinsic Semiconductors: The number of electrons and holes are entirely unequal. In n-type, electrons are majority carriers ($n_e \gg n_h$), whereas in p-type, holes are majority carriers ($n_h \gg n_e$).

Step 3: Conclusion
Intrinsic semiconductors have low conductivity that depends solely on temperature, whereas extrinsic semiconductors have high conductivity controlled by the doping concentration.