Which of the following is a pure semiconductor?

Step 1: Analyze the question The question asks which option is a pure (intrinsic) semiconductor. That means an element or material that is a semiconductor on its own, without added impurities (doping).

Step 2: Explain the concept

• A semiconductor has electrical conductivity between that of a conductor and an insulator.
• A pure (intrinsic) semiconductor is one with no impurity atoms added. The classic examples are silicon (Si) and germanium (Ge). Both are in Group IV of the periodic table and have 4 valence electrons.
• When impurities are added (doping), we get extrinsic semiconductors: • n-type: doped with Group V elements such as phosphorus, giving extra electrons. • p-type: doped with Group III elements such as boron, giving holes.

Step 3: Check each option

• A. Carbon: In its common forms (graphite, diamond), carbon is not used as a pure semiconductor. Graphite is a conductor and diamond is an insulator.
• B. Silicon: Yes, it is a pure semiconductor, widely used in electronics.
• C. Transistor: This is a device made from doped semiconductors, not a pure semiconductor material.
• D. Phosphorus: This is a dopant used to make n-type semiconductors, not itself the standard pure semiconductor.

Step 4: Answer The correct option is B. silicon.

Exam tip: Remember "Si and Ge are the pure ones." Phosphorus, arsenic, and antimony are n-type dopants (Group V), while boron, aluminium, and gallium are p-type dopants (Group III). A transistor is a device, not a material.