Question

An intrinsic semiconductor is converted into n-type extrinsic semiconductor by doping it with:

• A. Germanium
• B. Phosphorus
• C. Aluminium
• D. Silver

Hint:

Key points to remember:
- n-type has extra electrons from group 15 dopants (P, As, Sb)
- p-type has holes from group 13 dopants (B, Al, Ga)
- Pure Si/Ge have equal electrons and holes
- Doping controls conductivity type and magnitude

Answer 1

The Correct Option is B

Step 1: Understanding intrinsic semiconductors
An intrinsic semiconductor like pure silicon or germanium has equal numbers of electrons and holes. Its conductivity can be enhanced by adding impurity atoms through doping.
Step 2: Types of extrinsic semiconductors
Extrinsic semiconductors are of two types: n-type (electron rich) and p-type (hole rich). The type depends on the dopant used.
Step 3: Creating n-type semiconductors
To create n-type semiconductors, we use pentavalent impurities (5 valence electrons). These include phosphorus (P), arsenic (As), and antimony (Sb). They donate extra electrons as charge carriers.
Step 4: Analyzing the options
Germanium is not a dopant but a semiconductor itself. Aluminium is trivalent and creates p-type. Silver is not used for doping. Phosphorus is pentavalent and creates n-type.
Step 5: Why phosphorus works
Phosphorus (group 15) has 5 valence electrons. When doped into silicon (group 14), 4 electrons form covalent bonds while the 5th becomes a free electron, increasing electron concentration.