In ECET 2026 Physics, Semiconductors are a key topic. Questions are usually from definitions, types, doping, charge carriers, and energy band theory. Mastering this ensures scoring 2–3 direct marks.
📘 Concept Notes – Semiconductors (Basics)
🌐 What is a Semiconductor?
- A semiconductor is a material whose electrical conductivity lies between that of a conductor and an insulator.
- Examples: Silicon (Si), Germanium (Ge).
⚡ Types of Semiconductors
- Intrinsic Semiconductor:
- Pure form of semiconductor.
- Conductivity depends only on temperature.
- Equal number of electrons and holes.
- Extrinsic Semiconductor (Doped):
- Impurities are added to improve conductivity.
- Two types:
- n-type: Doped with pentavalent impurity (e.g., P, As). → More electrons.
- p-type: Doped with trivalent impurity (e.g., B, Al). → More holes.
⚙️ Important Formulas
- Electrical Conductivity
Where:
= charge carrier concentration
= charge of electron
= mobility
- Resistivity
Intrinsic Carrier Concentration
Where:
= energy band gap
= Boltzmann constant
= absolute temperature
- Energy Relation
Where:
= conduction band energy
= valence band energy
📐 Example
If intrinsic carrier concentration 
at 
for Si, then resistivity can be calculated using:
🔟 10 Expected MCQs – ECET 2026
Q1. Which of the following is a semiconductor?
A) Copper
B) Silicon
C) Glass
D) Wood
Q2. In intrinsic semiconductors, the number of electrons is:
A) Greater than holes
B) Equal to holes
C) Less than holes
D) Zero
Q3. The process of adding impurities to a semiconductor is called:
A) Mixing
B) Doping
C) Alloying
D) Annealing
Q4. n-type semiconductors are formed by doping with:
A) Trivalent impurity
B) Pentavalent impurity
C) Divalent impurity
D) None
Q5. Resistivity of a semiconductor is given by:
A) 
B)
C) 
D) 
Q6. Energy band gap of Silicon is approximately:
A) 0.7 eV
B) 1.1 eV
C) 3.2 eV
D) 5 eV
Q7. In p-type semiconductors, majority carriers are:
A) Electrons
B) Holes
C) Neutrons
D) None
Q8. Conductivity of semiconductors increases with:
A) Decrease in temperature
B) Increase in temperature
C) Constant temperature
D) None
Q9. Intrinsic carrier concentration 
is proportional to:
A) 
B)
C) 
D) 
Q10. Which statement is FALSE about semiconductors?
A) Conductivity lies between metals and insulators
B) Used in diodes and transistors
C) Doping decreases conductivity
D) Resistivity decreases with temperature
✅ Answer Key
| Q.No | Answer |
|---|---|
| Q1 | B |
| Q2 | B |
| Q3 | B |
| Q4 | B |
| Q5 | B |
| Q6 | B |
| Q7 | B |
| Q8 | B |
| Q9 | C |
| Q10 | C |
🧠 Explanations
- Q1 → B: Silicon is a semiconductor.
- Q2 → B: In intrinsic type, electrons = holes.
- Q3 → B: Adding impurities is called doping.
- Q4 → B: n-type formed by pentavalent impurity.
- Q5 → B: .
- Q6 → B: Si band gap = 1.1 eV.
- Q7 → B: Holes are majority carriers in p-type.
- Q8 → B: Conductivity increases with temperature.
- Q9 → C:
. - Q10 → C: Doping increases, not decreases, conductivity.
🎯 Why Practice Matters
- Semiconductor basics are repeated every year in ECET Physics.
- Very scoring: Most questions are direct definitions, formulas, and properties.
- Also forms the base for Electronics and Digital subjects.
