P-N Junction Diode – Forward Biasing (Simplified Notes)

What is a P-N Junction Diode?

• A basic semiconductor device formed by joining a P-type and N-type semiconductor.
• Mainly used for rectification (converting AC to DC).

Forward Biasing – Connection

• Battery positive terminal → connected to P-side
• Battery negative terminal → connected to N-side
• In this setup, the junction is called forward biased.

What Happens Inside (Fig. 9.4)

• An external electric field E is created, pointing from P to N.
• This field E is stronger than the junction's internal field Eᵢ (which normally opposes current flow).
• Because E > Eᵢ:
  • Holes (in P-region) move toward the junction.
  • Electrons (in N-region) move toward the junction.
• Holes and electrons penetrate into the depletion region.

Effect on Depletion Layer

• The depletion region width decreases.
• The potential barrier is reduced.
• As a result, more majority charge carriers can diffuse across the junction.

How Current Flows (Step-by-Step)

1. Charge carriers recombine at the junction (electron-hole recombination).
2. In the P-region: a covalent bond breaks near the battery's positive terminal → creates a new electron-hole pair.
   • The hole moves toward the junction.
   • The electron moves into the battery's positive terminal via the wire.
3. Simultaneously, an electron leaves the battery's negative terminal and enters the N-region, moving toward the junction.
4. This continuous motion of:
   • holes in the P-region, and
   • electrons in the N-region → creates current across the junction, called forward current.

Key Points

• Forward current is mainly due to majority carriers.
• A very small reverse current also exists due to minority carriers, but it's negligible.
• In the external circuit, current is carried only by electrons.
• Current keeps flowing as long as the battery stays connected.
• If battery voltage increases → barrier potential reduces further → more carriers diffuse → current increases (shown in Fig. 9.5, an exponential rise curve of I vs V).

Diagrams Referenced

• Fig. 9.4 – Circuit diagram showing forward bias of P-N junction (battery + polarity, depletion layer, carrier movement).
• Fig. 9.5 – Graph of Forward Current (I in mA) vs Voltage (V in volts) – shows current rises sharply as voltage increases.

Reverse Biasing of a P-N Junction Diode

Connection Setup

• Battery positive terminal → connected to the N-side
• Battery negative terminal → connected to the P-side
• This is opposite to forward biasing, and the junction is now called reverse biased.

What Happens Inside

• The applied electric field E (due to battery) now points in the same direction as the internal field Eᵢ of the junction.
• Since both fields act in the same direction, the net field across the junction increases.
• Because of this field:
  • Holes in the P-region are pushed away from the junction (toward the negative terminal).
  • Electrons in the N-region are pushed away from the junction (toward the positive terminal).

Effect on Depletion Layer

• Majority carriers move away from the junction, so very few of them cross it.
• The depletion region widens.
• The potential barrier increases.
• This makes it harder for majority carriers to diffuse across the junction.

Current Flow in Reverse Bias

• Since majority carriers move away from the junction, they contribute almost nothing to current flow.
• However, a small current does flow, called the reverse saturation current (I₀), caused by:
  • Minority carriers – electrons in the P-region and holes in the N-region, which are pulled across the junction by the applied field (since the field direction favors their motion).
• This reverse current is very small in magnitude, usually in the microampere (μA) range, compared to milliampere-range forward current.

Key Characteristics

• Reverse current is almost independent of the applied reverse voltage (over a normal working range) because it depends only on the number of minority carriers, which is fixed by temperature, not voltage.
• Reverse current increases with temperature, since more minority carriers are thermally generated at higher temperatures.
• If the reverse voltage is increased beyond a certain critical value (called the breakdown voltage), the current increases sharply and suddenly — this is called junction breakdown (Zener or avalanche breakdown), which can damage an ordinary diode.

I-V Characteristic (Reverse Bias)

• Graph of reverse current vs reverse voltage shows:
  • Current stays almost flat and very small (I₀) as voltage increases.
  • Then rises sharply once breakdown voltage is reached.

Comparison Summary

How Current Flows in Forward Bias (Step-by-Step)

Setup Recap

• Battery +ve terminal → connected to P-side
• Battery -ve terminal → connected to N-side
• Applied field E opposes and overcomes the internal junction field Eᵢ

Step-by-Step Current Flow

• Since E > Eᵢ, the depletion region narrows and the potential barrier is reduced.
• This allows majority carriers to diffuse across the junction easily.

• Holes in the P-region move toward the junction (pushed by the field, and by repulsion from the +ve battery terminal).
• Electrons in the N-region move toward the junction (pushed by the field, and by repulsion from the -ve battery terminal).

• At the junction, holes (from P-side) and electrons (from N-side) meet and recombine.

• Each recombination event needs to be "replaced" for current to keep flowing continuously:
  • In the P-region, near the battery's +ve terminal, a covalent bond breaks, creating a new electron-hole pair.
    • The hole moves toward the junction (to replace the one that recombined).
    • The electron moves into the battery's +ve terminal through the connecting wire.
  • At the same instant, in the N-region, an electron leaves the battery's -ve terminal, enters the N-region, and moves toward the junction (replacing the electron that recombined).

• This continuous process, holes flowing from P toward the junction and electrons flowing from N toward the junction, constitutes a steady forward current across the diode.
• This current is carried mainly by majority carriers (holes in P, electrons in N).
• A tiny reverse current also exists due to minority carriers, but it is negligible compared to the forward current.

Current in the External Circuit

• Inside the diode: current is carried by both holes (P-side) and electrons (N-side) moving toward each other.
• In the external circuit (the wires and battery): current is carried only by electrons, since only electrons can exist and move in the metal wires.

Effect of Increasing Voltage

• As battery voltage is increased, the potential barrier is reduced further.
• More majority carriers diffuse across the junction, so the forward current increases rapidly.
• This is shown by the exponential rise in the I-V graph (Fig. 9.5: current in mA rises sharply as voltage increases).

Quick Summary

Majority Charge Carrier

Definition

• The type of charge carrier that is present in larger number in a semiconductor material, and is mainly responsible for conduction of current in it.

In P-type Semiconductor

• Holes are the majority charge carriers.
• Created by doping a pure (intrinsic) semiconductor with a trivalent impurity (like Boron, Aluminium, Gallium, Indium).
• These impurity atoms have only 3 valence electrons, so when they bond with the semiconductor atoms (4 valence electrons), one bond is left incomplete, creating a hole (absence of an electron).
• Electrons here are the minority carriers.

In N-type Semiconductor

• Free electrons are the majority charge carriers.
• Created by doping a pure semiconductor with a pentavalent impurity (like Phosphorus, Arsenic, Antimony).
• These impurity atoms have 5 valence electrons; 4 form bonds with the semiconductor atoms, and the 5th electron remains free to move, becoming a majority carrier.
• Holes here are the minority carriers.

Quick Comparison

Relevance to P-N Junction Diode

• In forward bias: current flow is mainly due to the motion of majority carriers (holes in P-region move toward the junction, electrons in N-region move toward the junction) — this gives a large current.
• In reverse bias: majority carriers are pushed away from the junction, so current is instead due to the small number of minority carriers, giving a very small (negligible) current.

Reverse Bias of P-N Junction Diode (Simplified Notes)

What is Reverse Biasing?

• When a battery is connected to a P-N junction diode such that the positive terminal of the battery is connected to the N-side and the negative terminal to the P-side, the P-N junction is said to be reverse biased.

Connection (like Fig. 9.4, but reversed)

• P-side → connected to battery's negative terminal
• N-side → connected to battery's positive terminal

What Happens Inside

• An external electric field E is established, directed from N to P (opposite direction compared to forward bias).
• This field E acts in the same direction as the internal field Eᵢ of the junction (unlike forward bias, where E opposes Eᵢ).
• Because both fields point the same way, the net field across the junction increases.
• Due to this combined field:
  • Holes in the P-region are pushed away from the junction, toward the negative terminal.
  • Electrons in the N-region are pushed away from the junction, toward the positive terminal.

Effect on Depletion Layer

• Since majority carriers move away from the junction (instead of toward it), very few of them cross over.
• The width of the depletion region increases.
• The potential barrier increases.
• This makes it very difficult for majority carriers to diffuse across the junction.

How Current Flows (Step-by-Step)

1. Majority carriers (holes in P, electrons in N) are pulled away from the junction, so they don't contribute to conduction across it.
2. However, the minority carriers — electrons present in the P-region and holes present in the N-region — experience a favorable field direction and get pulled across the junction.
3. This motion of minority carriers constitutes a small current, known as the reverse saturation current (I₀).
4. As with forward bias, current in the external circuit is carried only by electrons through the connecting wires.
5. This reverse current continues as long as the battery is connected, but its magnitude stays very small (microampere range) and remains almost constant, regardless of how much the reverse voltage is increased — because it depends on the fixed number of thermally generated minority carriers, not on voltage.

Key Points

• Reverse current is due to the motion of minority carriers, unlike forward current which is due to majority carriers.
• Reverse current is very small (μA) compared to forward current (mA).
• Reverse current increases with temperature, since heat generates more minority carriers.
• If reverse voltage is increased beyond a critical limit (the breakdown voltage), the current suddenly rises sharply — this is called junction breakdown, and it can permanently damage an ordinary diode.

I-V Graph (Reverse Bias)

• Current stays almost flat and very small as reverse voltage increases.
• Then rises abruptly once the breakdown voltage is reached (opposite trend compared to the sharply-rising exponential curve seen in forward bias, Fig. 9.5).

Intrinsic vs Extrinsic Semiconductor

Intrinsic Semiconductor

• A semiconductor in its pure form, without any impurity added.
• Example: Pure Silicon (Si), Pure Germanium (Ge).

• Contains equal numbers of free electrons and holes.
• These carriers are generated purely due to thermal energy breaking covalent bonds (electron-hole pairs created in equal pairs).

• Very low conductivity at room temperature.
• Conductivity increases with temperature, since more electron-hole pairs are generated as heat increases.
• Cannot be controlled or adjusted since there's no doping involved.

• Number of free electrons (nₑ) = Number of holes (nₕ)

Extrinsic Semiconductor

• A semiconductor formed by adding a small amount of impurity (doping) to a pure/intrinsic semiconductor, to increase its conductivity.
• Example: Silicon doped with Boron (P-type), Silicon doped with Phosphorus (N-type).

• Contains unequal numbers of electrons and holes, one type dominates:
  • N-type: doped with pentavalent impurity (e.g. Phosphorus, Arsenic) → free electrons are majority carriers, holes are minority carriers.
  • P-type: doped with trivalent impurity (e.g. Boron, Aluminium) → holes are majority carriers, electrons are minority carriers.

• Much higher conductivity than intrinsic semiconductor, even at room temperature.
• Conductivity can be controlled by varying the amount/type of doping.

• Number of majority carriers is much greater than minority carriers.

Quick Comparison Table

Semiconductor Electronics (Class 12, MP Board) — Objective Questions Overview

Topic Breakdown

1. Basics of Semiconductors – energy bands, conductor vs insulator vs semiconductor, intrinsic semiconductor
2. Doping & Extrinsic Semiconductors – P-type, N-type, trivalent/pentavalent impurities, majority/minority carriers
3. P-N Junction Diode – formation, depletion layer, potential barrier
4. Forward & Reverse Biasing – current flow, I-V characteristics
5. Diode Applications – half-wave & full-wave rectifiers, ripple factor
6. Special Purpose Diodes – Zener diode (voltage regulation), LED, photodiode, solar cell
7. Transistors – NPN/PNP structure, working, transistor as a switch, transistor as an amplifier (CE configuration)
8. Digital Electronics / Logic Gates – NOT, AND, OR, NAND, NOR gates, truth tables, Boolean expressions

Brief Overview

P-N Junction Diode – Forward Biasing (Simplified Notes)

What is a P-N Junction Diode?

• A basic semiconductor device formed by joining a P-type and N-type semiconductor.
• Mainly used for rectification (converting AC to DC).

Forward Biasing – Connection

• Battery positive terminal → connected to P-side
• Battery negative terminal → connected to N-side
• In this setup, the junction is called forward biased.

What Happens Inside (Fig. 9.4)

• An external electric field E is created, pointing from P to N.
• This field E is stronger than the junction's internal field Eᵢ (which normally opposes current flow).
• Because E > Eᵢ:
  • Holes (in P-region) move toward the junction.
  • Electrons (in N-region) move toward the junction.
• Holes and electrons penetrate into the depletion region.

Effect on Depletion Layer

• The depletion region width decreases.
• The potential barrier is reduced.
• As a result, more majority charge carriers can diffuse across the junction.

How Current Flows (Step-by-Step)

1. Charge carriers recombine at the junction (electron-hole recombination).
2. In the P-region: a covalent bond breaks near the battery's positive terminal → creates a new electron-hole pair.
   • The hole moves toward the junction.
   • The electron moves into the battery's positive terminal via the wire.
3. Simultaneously, an electron leaves the battery's negative terminal and enters the N-region, moving toward the junction.
4. This continuous motion of:
   • holes in the P-region, and
   • electrons in the N-region → creates current across the junction, called forward current.

Key Points

• Forward current is mainly due to majority carriers.
• A very small reverse current also exists due to minority carriers, but it's negligible.
• In the external circuit, current is carried only by electrons.
• Current keeps flowing as long as the battery stays connected.
• If battery voltage increases → barrier potential reduces further → more carriers diffuse → current increases (shown in Fig. 9.5, an exponential rise curve of I vs V).

Diagrams Referenced

• Fig. 9.4 – Circuit diagram showing forward bias of P-N junction (battery + polarity, depletion layer, carrier movement).
• Fig. 9.5 – Graph of Forward Current (I in mA) vs Voltage (V in volts) – shows current rises sharply as voltage increases.# Reverse Biasing of a P-N Junction Diode

Connection Setup

• Battery positive terminal → connected to the N-side
• Battery negative terminal → connected to the P-side
• This is opposite to forward biasing, and the junction is now called reverse biased.

What Happens Inside

• The applied electric field E (due to battery) now points in the same direction as the internal field Eᵢ of the junction.
• Since both fields act in the same direction, the net field across the junction increases.
• Because of this field:
  • Holes in the P-region are pushed away from the junction (toward the negative terminal).
  • Electrons in the N-region are pushed away from the junction (toward the positive terminal).

Effect on Depletion Layer

• Majority carriers move away from the junction, so very few of them cross it.
• The depletion region widens.
• The potential barrier increases.
• This makes it harder for majority carriers to diffuse across the junction.

Current Flow in Reverse Bias

• Since majority carriers move away from the junction, they contribute almost nothing to current flow.
• However, a small current does flow, called the reverse saturation current (I₀), caused by:
  • Minority carriers – electrons in the P-region and holes in the N-region, which are pulled across the junction by the applied field (since the field direction favors their motion).
• This reverse current is very small in magnitude, usually in the microampere (μA) range, compared to milliampere-range forward current.

Key Characteristics

• Reverse current is almost independent of the applied reverse voltage (over a normal working range) because it depends only on the number of minority carriers, which is fixed by temperature, not voltage.
• Reverse current increases with temperature, since more minority carriers are thermally generated at higher temperatures.
• If the reverse voltage is increased beyond a certain critical value (called the breakdown voltage), the current increases sharply and suddenly — this is called junction breakdown (Zener or avalanche breakdown), which can damage an ordinary diode.

I-V Characteristic (Reverse Bias)

• Graph of reverse current vs reverse voltage shows:
  • Current stays almost flat and very small (I₀) as voltage increases.
  • Then rises sharply once breakdown voltage is reached.

Comparison Summary

Setup Recap

• Battery +ve terminal → connected to P-side
• Battery -ve terminal → connected to N-side
• Applied field E opposes and overcomes the internal junction field Eᵢ

Step-by-Step Current Flow

• Since E > Eᵢ, the depletion region narrows and the potential barrier is reduced.
• This allows majority carriers to diffuse across the junction easily.

• Holes in the P-region move toward the junction (pushed by the field, and by repulsion from the +ve battery terminal).
• Electrons in the N-region move toward the junction (pushed by the field, and by repulsion from the -ve battery terminal).

• At the junction, holes (from P-side) and electrons (from N-side) meet and recombine.

• Each recombination event needs to be "replaced" for current to keep flowing continuously:
  • In the P-region, near the battery's +ve terminal, a covalent bond breaks, creating a new electron-hole pair.
    • The hole moves toward the junction (to replace the one that recombined).
    • The electron moves into the battery's +ve terminal through the connecting wire.
  • At the same instant, in the N-region, an electron leaves the battery's -ve terminal, enters the N-region, and moves toward the junction (replacing the electron that recombined).

• This continuous process, holes flowing from P toward the junction and electrons flowing from N toward the junction, constitutes a steady forward current across the diode.
• This current is carried mainly by majority carriers (holes in P, electrons in N).
• A tiny reverse current also exists due to minority carriers, but it is negligible compared to the forward current.

Current in the External Circuit

• Inside the diode: current is carried by both holes (P-side) and electrons (N-side) moving toward each other.
• In the external circuit (the wires and battery): current is carried only by electrons, since only electrons can exist and move in the metal wires.

Effect of Increasing Voltage

• As battery voltage is increased, the potential barrier is reduced further.
• More majority carriers diffuse across the junction, so the forward current increases rapidly.
• This is shown by the exponential rise in the I-V graph (Fig. 9.5: current in mA rises sharply as voltage increases).

Quick Summary

Definition

• The type of charge carrier that is present in larger number in a semiconductor material, and is mainly responsible for conduction of current in it.

In P-type Semiconductor

• Holes are the majority charge carriers.
• Created by doping a pure (intrinsic) semiconductor with a trivalent impurity (like Boron, Aluminium, Gallium, Indium).
• These impurity atoms have only 3 valence electrons, so when they bond with the semiconductor atoms (4 valence electrons), one bond is left incomplete, creating a hole (absence of an electron).
• Electrons here are the minority carriers.

In N-type Semiconductor

• Free electrons are the majority charge carriers.
• Created by doping a pure semiconductor with a pentavalent impurity (like Phosphorus, Arsenic, Antimony).
• These impurity atoms have 5 valence electrons; 4 form bonds with the semiconductor atoms, and the 5th electron remains free to move, becoming a majority carrier.
• Holes here are the minority carriers.

Quick Comparison

Relevance to P-N Junction Diode

• In forward bias: current flow is mainly due to the motion of majority carriers (holes in P-region move toward the junction, electrons in N-region move toward the junction) — this gives a large current.
• In reverse bias: majority carriers are pushed away from the junction, so current is instead due to the small number of minority carriers, giving a very small (negligible) current.# Reverse Bias of P-N Junction Diode (Simplified Notes)

What is Reverse Biasing?

• When a battery is connected to a P-N junction diode such that the positive terminal of the battery is connected to the N-side and the negative terminal to the P-side, the P-N junction is said to be reverse biased.

Connection (like Fig. 9.4, but reversed)

• P-side → connected to battery's negative terminal
• N-side → connected to battery's positive terminal

What Happens Inside

• An external electric field E is established, directed from N to P (opposite direction compared to forward bias).
• This field E acts in the same direction as the internal field Eᵢ of the junction (unlike forward bias, where E opposes Eᵢ).
• Because both fields point the same way, the net field across the junction increases.
• Due to this combined field:
  • Holes in the P-region are pushed away from the junction, toward the negative terminal.
  • Electrons in the N-region are pushed away from the junction, toward the positive terminal.

Effect on Depletion Layer

• Since majority carriers move away from the junction (instead of toward it), very few of them cross over.
• The width of the depletion region increases.
• The potential barrier increases.
• This makes it very difficult for majority carriers to diffuse across the junction.

How Current Flows (Step-by-Step)

1. Majority carriers (holes in P, electrons in N) are pulled away from the junction, so they don't contribute to conduction across it.
2. However, the minority carriers — electrons present in the P-region and holes present in the N-region — experience a favorable field direction and get pulled across the junction.
3. This motion of minority carriers constitutes a small current, known as the reverse saturation current (I₀).
4. As with forward bias, current in the external circuit is carried only by electrons through the connecting wires.
5. This reverse current continues as long as the battery is connected, but its magnitude stays very small (microampere range) and remains almost constant, regardless of how much the reverse voltage is increased — because it depends on the fixed number of thermally generated minority carriers, not on voltage.

Key Points

• Reverse current is due to the motion of minority carriers, unlike forward current which is due to majority carriers.
• Reverse current is very small (μA) compared to forward current (mA).
• Reverse current increases with temperature, since heat generates more minority carriers.
• If reverse voltage is increased beyond a critical limit (the breakdown voltage), the current suddenly rises sharply — this is called junction breakdown, and it can permanently damage an ordinary diode.

I-V Graph (Reverse Bias)

• Current stays almost flat and very small as reverse voltage increases.
• Then rises abruptly once the breakdown voltage is reached (opposite trend compared to the sharply-rising exponential curve seen in forward bias, Fig. 9.5).# Intrinsic vs Extrinsic Semiconductor

Intrinsic Semiconductor

• A semiconductor in its pure form, without any impurity added.
• Example: Pure Silicon (Si), Pure Germanium (Ge).

• Contains equal numbers of free electrons and holes.
• These carriers are generated purely due to thermal energy breaking covalent bonds (electron-hole pairs created in equal pairs).

• Very low conductivity at room temperature.
• Conductivity increases with temperature, since more electron-hole pairs are generated as heat increases.
• Cannot be controlled or adjusted since there's no doping involved.

• Number of free electrons (nₑ) = Number of holes (nₕ)

Extrinsic Semiconductor

• A semiconductor formed by adding a small amount of impurity (doping) to a pure/intrinsic semiconductor, to increase its conductivity.
• Example: Silicon doped with Boron (P-type), Silicon doped with Phosphorus (N-type).

• Contains unequal numbers of electrons and holes, one type dominates:
  • N-type: doped with pentavalent impurity (e.g. Phosphorus, Arsenic) → free electrons are majority carriers, holes are minority carriers.
  • P-type: doped with trivalent impurity (e.g. Boron, Aluminium) → holes are majority carriers, electrons are minority carriers.

• Much higher conductivity than intrinsic semiconductor, even at room temperature.
• Conductivity can be controlled by varying the amount/type of doping.

• Number of majority carriers is much greater than minority carriers.

Quick Comparison Table

Topic Breakdown

1. Basics of Semiconductors – energy bands, conductor vs insulator vs semiconductor, intrinsic semiconductor
2. Doping & Extrinsic Semiconductors – P-type, N-type, trivalent/pentavalent impurities, majority/minority carriers
3. P-N Junction Diode – formation, depletion layer, potential barrier
4. Forward & Reverse Biasing – current flow, I-V characteristics
5. Diode Applications – half-wave & full-wave rectifiers, ripple factor
6. Special Purpose Diodes – Zener diode (voltage regulation), LED, photodiode, solar cell
7. Transistors – NPN/PNP structure, working, transistor as a switch, transistor as an amplifier (CE configuration)
8. Digital Electronics / Logic Gates – NOT, AND, OR, NAND, NOR gates, truth tables, Boolean expressions

Brief Overview

Semiconductor Electronics – Important Objective Questions (MP Board, Class 12)

1. Basics of Semiconductors (Energy Bands, Intrinsic Semiconductor)

1. Q: The energy gap of a semiconductor is of the order of: A: 1 eV (approx.) (e.g., Si ≈ 1.1 eV, Ge ≈ 0.7 eV)
2. Q: In an intrinsic semiconductor, the number of free electrons is: A: Equal to the number of holes
3. Q: At absolute zero temperature (0 K), a pure semiconductor behaves as a/an: A: Insulator (no free carriers available)
4. Q: The energy gap of an insulator is: A: Very large (> 3 eV, e.g. diamond ≈ 5.4 eV)
5. Q: As temperature increases, the resistance of a semiconductor: A: Decreases (conductivity increases)
6. Q (Fill in blank): In a conductor, the valence band and conduction band _______. A: Overlap

2. Doping & Extrinsic Semiconductors

1. Q: Which impurity is added to Silicon to make a P-type semiconductor? A: Trivalent impurity (e.g., Boron, Aluminium, Indium, Gallium)
2. Q: Which impurity is added to Silicon to make an N-type semiconductor? A: Pentavalent impurity (e.g., Phosphorus, Arsenic, Antimony)
3. Q: In N-type semiconductor, majority carriers are: A: Free electrons
4. Q: In P-type semiconductor, minority carriers are: A: Electrons
5. Q: A pentavalent impurity atom is also called a/an: A: Donor impurity (donates an electron)
6. Q: A trivalent impurity atom is also called a/an: A: Acceptor impurity (accepts an electron, creates a hole)
7. Q (True/False): Doped semiconductors are electrically neutral overall. A: True

3. P-N Junction Diode

1. Q: A P-N junction diode is formed by joining: A: A P-type and N-type semiconductor
2. Q: The region near the junction depleted of free charge carriers is called: A: Depletion region/layer
3. Q: The potential difference developed across the depletion layer is called: A: Barrier potential / Junction potential (≈ 0.7 V for Si, ≈ 0.3 V for Ge)
4. Q: The direction of the internal electric field (Eᵢ) at a P-N junction is from: A: N-region to P-region
5. Q (Fill in blank): The symbol of a diode has an arrow pointing from _______ to _______. A: P (anode) to N (cathode)

4. Forward & Reverse Biasing

1. Q: In forward biasing, the positive terminal of battery is connected to: A: P-side
2. Q: In reverse biasing, the positive terminal of battery is connected to: A: N-side
3. Q: In forward bias, the width of depletion layer: A: Decreases
4. Q: In reverse bias, the width of depletion layer: A: Increases
5. Q: Forward current in a diode is due to: A: Majority charge carriers
6. Q: Reverse current in a diode is due to: A: Minority charge carriers
7. Q: The current in external circuit connected to a diode is always carried by: A: Electrons only
8. Q: The sudden, large increase in reverse current at high reverse voltage is called: A: Breakdown (Zener/Avalanche breakdown)
9. Q (True/False): A diode conducts current equally well in both directions. A: False (it conducts mainly in forward direction — this property is called rectification)

5. Rectifiers (Diode Application)

1. Q: A device that converts AC into DC is called a: A: Rectifier
2. Q: Number of diodes used in a half-wave rectifier: A: 1
3. Q: Number of diodes used in a full-wave rectifier: A: 2 (center-tap) or 4 (bridge rectifier)
4. Q: Which rectifier has higher efficiency, half-wave or full-wave? A: Full-wave rectifier
5. Q: The output of a half-wave rectifier is obtained for: A: Only one half cycle of the AC input
6. Q: The component used to smoothen rectifier output (reduce ripples) is a: A: Capacitor filter

6. Special Purpose Diodes

1. Q: A Zener diode is mainly used as a: A: Voltage regulator
2. Q: A Zener diode works in which region of its characteristic? A: Reverse breakdown region
3. Q: LED stands for: A: Light Emitting Diode
4. Q: LED works when connected in: A: Forward bias
5. Q: A photodiode works in which biasing? A: Reverse bias
6. Q: A photodiode converts: A: Light energy into electrical current
7. Q: A solar cell works on the principle of: A: Photovoltaic effect (converts light energy directly into electrical energy, no external bias needed)

7. Transistors

1. Q: A transistor has how many P-N junctions? A: Two (Emitter-Base junction and Collector-Base junction)
2. Q: The three terminals of a transistor are: A: Emitter (E), Base (B), Collector (C)
3. Q: Which region of a transistor is very thin and lightly doped? A: Base
4. Q: In a transistor, the Emitter-Base junction is _______ biased and Collector-Base junction is _______ biased (for normal/active operation). A: Forward biased; Reverse biased
5. Q: Current amplification factor in common base configuration is denoted by: A: α (alpha) = Iс/Iₑ (always < 1)
6. Q: Current amplification factor in common emitter configuration is denoted by: A: β (beta) = Iс/I_b (always > 1)
7. Q: Relation between α and β: A: β = α / (1 - α)
8. Q: Which transistor configuration is most commonly used as an amplifier? A: Common Emitter (CE) configuration
9. Q: A transistor used as a switch operates in which two states? A: Cut-off (OFF) and Saturation (ON)

8. Digital Electronics / Logic Gates

1. Q: The basic logic gates are: A: OR, AND, NOT
2. Q: NAND gate is a combination of: A: AND gate followed by NOT gate
3. Q: NOR gate is a combination of: A: OR gate followed by NOT gate
4. Q: Which gates are called "Universal Gates" (can be used to build all other gates)? A: NAND and NOR
5. Q: Output of an AND gate is HIGH (1) only when: A: All inputs are HIGH (1)
6. Q: Output of an OR gate is LOW (0) only when: A: All inputs are LOW (0)
7. Q: A NOT gate is also called a/an: A: Inverter (has only 1 input, 1 output)
8. Q (Fill in blank): Boolean expression for NAND gate: Y = _______ A: Y = (A.B)' or NOT(A AND B)
9. Q (Fill in blank): Boolean expression for NOR gate: Y = _______ A: Y = (A+B)' or NOT(A OR B)