💻 SEMICONDUCTOR ELECTRONICS · Materials, Devices & Circuits
Energy bands • Intrinsic/extrinsic • p‑n junction • Diodes • Transistors • Logic gates • NEET problems
⚡ ENERGY BANDS IN SOLIDS
Valence band, conduction band, forbidden gap (Eg).
Conductors: Eg = 0 (overlap).
Insulators: Eg > 3 eV.
Semiconductors: Eg ≈ 1 eV (Si: 1.1 eV, Ge: 0.7 eV).
📊 Energy band diagram
🔬 INTRINSIC & EXTRINSIC SEMICONDUCTORS
Intrinsic (pure): ne = nh = ni.
n‑type (doped with pentavalent): ne >> nh (majority = electrons). Donor level near CB.
p‑type (doped with trivalent): nh >> ne (majority = holes). Acceptor level near VB.
Mass action law: ne nh = ni²
🧬 n‑type & p‑type crystal structures
🔌 p‑n JUNCTION DIODE
Formed by joining p‑type and n‑type semiconductors. Depletion region created, built‑in potential barrier (~0.7V for Si, 0.3V for Ge).
Forward bias: p to +, n to – → barrier reduced, current flows.
Reverse bias: p to –, n to + → barrier increased, small leakage current.
I–V equation: I = I₀(eeV/kT – 1).
📈 p‑n junction I‑V characteristic
⚙️ DIODE APPLICATIONS
Rectifiers
Half‑wave: η = 40.6%
Full‑wave (bridge): η = 81.2%
Ripple factor: r = √(Vrms²/Vdc² – 1).
Zener Diode
Operates in reverse breakdown → voltage regulator.
LED & Photodiode
LED: forward bias → light emission.
Photodiode: reverse bias → light detection.
🔧 BIPOLAR JUNCTION TRANSISTOR (BJT)
Three regions: emitter (E), base (B), collector (C). Types: npn & pnp.
Transistor action: IE = IB + IC, IC = β IB (β = current gain).
Common emitter configuration: voltage gain Av = –β RC/RB.
📊 Transistor symbol & biasing
🔘 LOGIC GATES
NOT
Y = Ā
Truth table: 0→1, 1→0.
AND
Y = A·B
Output 1 only if both inputs are 1.
OR
Y = A+B
Output 1 if any input is 1.
NAND
Y = (A·B)′
Universal gate.
NOR
Y = (A+B)′
Universal gate.
XOR
Y = A⊕B = A′B + AB′
🧩 Logic gate symbols
💡 NEET TIPS & SHORTCUTS
- In intrinsic semiconductor, ni ∝ T3/2 e–Eg/2kT.
- For a diode, forward voltage drop is constant (≈0.7V Si) in simplified model.
- Transistor β = IC/IB (typical 50–300).
- NAND and NOR are universal gates (can implement any logic).
⚠️ COMMON MISTAKES
- Confusing n‑type (electrons majority) with p‑type (holes majority).
- Applying Ohm's law to p‑n junction – it's non‑ohmic.
- Forgetting that in forward bias, potential barrier reduces.
- Mixing up logic gate truth tables.
📌 QUICK REVISION CARD
ne nh = ni²
Diode I‑V: I = I₀(eeV/kT–1)
Rectifier efficiency (FW): 81.2%
Transistor: IC = β IB
Common emitter gain: Av = –β RC/RB
Logic gates: AND (·), OR (+), NOT (′)
💡 SEMICONDUCTORS • NEET REVISION NOTES
📸 NOTES PREVIEW
Preview of Semiconductors Notes
📥 DOWNLOAD SEMICONDUCTORS NOTES PDF
Download Semiconductors Revision Notes for NEET Physics PDF for quick revision and strong conceptual clarity. This chapter is one of the most important and easy scoring topics in Modern Physics for NEET.
These Semiconductors handwritten notes PDF free download include p-n junction diode, Zener diode, transistor, logic gates, and all important concepts, tricks, and PYQ-based questions.
- Direct theory-based questions in NEET
- Logic gates are frequently asked
- Very easy and scoring chapter
- Less calculation, more concept clarity
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📊 WEIGHTAGE ANALYSIS
1–2 Questions
Logic gates + diode
High Weightage
Theory-based questions
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