Semiconductor Electronics for NEET UG
Semiconductors are the materials inside every phone, computer and LED. Learn how doping, the p–n junction and logic gates make electronics work.
PhysicsClass 1260 MCQs3 lessons13 flashcards3 memory tricks
Practise Semiconductor Electronics free
What you'll learn
- Energy bands and doping
Tell conductors, semiconductors and insulators apart by band gap, and explain n-type and p-type doping. - The p–n junction diode
Explain forward and reverse bias, and how a diode rectifies AC. - Special diodes and logic gates
Match special-purpose diodes to their uses and write truth tables for basic logic gates.
Memory tricks
Pentavalent dopants (P, As, Sb) give an extra electron, making n-type. Trivalent dopants (B, Al, Ga, In) create holes, making p-type.
In forward bias the p side goes to the positive terminal; the depletion layer narrows and current flows. Reverse bias widens it and almost no current flows.
AND gives 1 only if all inputs are 1; OR gives 1 if any input is 1. NAND and NOR are universal gates: every other gate can be built from them alone.
Try 3 NEET-style questions
Q1. A silicon diode has a forward voltage drop of 0.7 V. In series with a 2 kΩ resistor across 5 V, the current is about
- 2.5 mA
- 0.35 mA
- 2.15 mA
- 3.6 mA
Show answer
Answer: (3) 2.15 mA
I = (5 − 0.7)/2000 = 2.15 mA.
Q2. Which gates are called universal gates, because any logic circuit can be built from them alone?
- AND and OR
- OR and NOT
- AND and NOT
- NAND and NOR
Show answer
Answer: (4) NAND and NOR
Using only NAND gates (or only NOR gates), one can build NOT, AND and OR, and hence any logic circuit.
Q3. The depletion region of a p-n junction contains
- immobile positive and negative ions
- only free electrons
- only free holes
- a large number of free electrons and holes
Show answer
Answer: (1) immobile positive and negative ions
Near the junction, electrons and holes recombine, leaving fixed donor (+) and acceptor (−) ions. These immobile ions form the depletion region.
Practise all 60 questions Free · explanations for every option · see where you go wrong