Semiconductor Diode MCQ Quiz - Objective Question with Answer for Semiconductor Diode - Download Free PDF

The correct answer is Both Statement I and Statement II are incorrect.

Key Points

• Photovoltaic devices convert optical radiation into electricity. These devices, such as solar panels, utilize the photovoltaic effect to generate electrical energy from light energy.
• The photovoltaic effect is a process in which light photons are absorbed by a material, typically a semiconductor, causing the release of electrons and creating an electric current.
• Zener diodes are designed to operate in the reverse bias condition, specifically in the breakdown region.
• In the breakdown region, a Zener diode allows current to flow in the reverse direction when the voltage exceeds the breakdown voltage, which is a characteristic feature of Zener diodes.
• Zener diodes are commonly used for voltage regulation in electronic circuits, ensuring a stable output voltage despite variations in the input voltage or load conditions.

 Additional Information

• Statement I
  • Photovoltaic devices are crucial in renewable energy systems, particularly in solar power generation, where they convert sunlight directly into electricity.
  • These devices are made of materials such as silicon, which have properties that allow them to absorb photons and release electrons, creating an electric current.
• Statement II
  • Zener diodes are specifically designed to maintain a constant voltage across their terminals when reverse-biased and the applied voltage reaches the Zener breakdown voltage.
  • This property makes Zener diodes useful in applications requiring precise voltage regulation, such as power supplies and voltage reference circuits.

Concept Used:

The Zener diode operates in reverse breakdown mode and maintains a constant voltage across it, irrespective of changes in input voltage or load resistance.

For a maximum current calculation , we consider the highest supply voltage (100V).

The voltage drop across the series resistors (R₁ and R₂) can be determined as:

V_R1+R2 = V_input - V_Zener

where:

V_input = 100V

V_Zener = 30V

Calculation:

Voltage across 5kΩ + 2kΩ resistors :

V_R1+R2 = 100V - 30V = 70V

Total resistance in series:

R_total = 5kΩ + 2kΩ = 7kΩ

Total current through the circuit:

I_total = V_R1+R2 / R_total

I_total = 70V / 7kΩ

I_total = 10 mA

Current through 6kΩ resistor (load current):

I_load = V_Zener / R_load

I_load = 30V / 6kΩ

I_load = 5 mA

Zener diode current:

I_Zener = I_total - I_load

I_Zener = 10 mA - 5 mA

I_Zener = 5 mA

∴ The maximum current through the Zener diode is 5 mA.

Concept:

Intrinsic and Doped Semiconductor:

• In an intrinsic semiconductor, the electron concentration (nᵢ) is equal to the hole concentration (pᵢ), and they are related by the equation:
  nᵢ = pᵢ = 6 × 10¹⁵ m⁻³ (Given for intrinsic semiconductor)
• When a semiconductor is doped, the electron concentration increases, and the hole concentration decreases. However, in thermal equilibrium, the product of the electron concentration (n) and the hole concentration (p) remains constant and is given by:
  n × p = nᵢ²
• After doping, the electron concentration (n) increases to 4 × 10²² m⁻³. The concentration of holes (p) can be found using the above relation, where nᵢ² is the product of the intrinsic carrier concentration.
• So, in thermal equilibrium, the hole concentration is:
  p = nᵢ² / n

Calculation:

Given,

Initial electron concentration in intrinsic semiconductor, nᵢ = 6 × 10¹⁵ m⁻³

After doping, the electron concentration, n = 4 × 10²² m⁻³

The product of electron and hole concentration is given by:

n × p = nᵢ²

p = nᵢ² / n = (6 × 10¹⁵)² / (4 × 10²²)

p = 36 × 10³⁰ / 4 × 10²²

p = 9 × 10⁸ m⁻³

∴ The concentration of holes in the doped semiconductor is 9 × 10⁸ m⁻³.
Hence, the correct option is 3) 9 × 10⁸ m⁻³.

Given:

A Zener diode is connected in the reverse breakdown region with a series resistor R_S and load resistor R_L. The input voltage is V₀, the Zener voltage is V_Z, and the current through the load resistance is I_L. We need to calculate the current through the Zener diode, I_Z.

Concept:

• In a Zener diode circuit, the total current through the series resistor R_S splits into two parts:
  • Current through the load resistance R_L: I_L.
  • Current through the Zener diode: I_Z.
• Using Kirchhoff's Voltage Law (KVL) for the input loop:

  V₀ - I_SR_S - V_Z = 0.

  Therefore, the total current through the series resistor is:

  I_S = (V₀ - V_Z) / R_S.

• The current through the Zener diode is the difference between the total current I_S and the load current I_L:

  I_Z = I_S - I_L.

Calculation:

Step-by-step calculation:

1. Total current through the series resistor:

I_S = (V₀ - V_Z) / R_S.

2. Current through the Zener diode:

I_Z = I_S - I_L.

Substitute I_S:

I_Z = (V₀ - V_Z) / R_S - I_L.

∴ The current through the Zener diode is ((V₀ - V_Z) / R_S) - I_L.

The correct option is 4)

​Explanation:

A. Zener Diode - Zener diodes are commonly used for voltage regulation. So, A matches with II (Voltage Regulator).

B. LED - LEDs are used for displays and indicators, often in remote control systems, so B matches with III (Remote Control).

C. Rectifier - A rectifier converts AC to DC, so C matches with IV (AC to DC).

D. Photo Diode - Photo diodes are used to detect optical signals, so D matches with I (Detect optical signals).

Correct Answer: Option 4) A - II, B - IV, C - I, D - III

CONCEPT:​

Zener diode: 

• A Semiconductor Diode blocks current in the reverse direction but will suffer from premature breakdown or damage if the reverse voltage applied across becomes too high.

EXPLANATION:

Zener diode as a voltage regulator: 

• The Zener diode is connected with its cathode terminal connected to the positive rail of the DC supply so it is reverse biased and will be operating in its breakdown condition.
• Resistor Rs is selected so as to limit the maximum current flowing in the circuit.

• A Zener diode is used as a voltage regulator in reverse biased mode.
• The breakdown voltage in the Zener diode when connected in the reverse-biased is called Zener voltage. This Zener voltage so steady and constant, it has huge applications in circuits, most importantly, voltage regulation. Therefore option 4 is correct.

CONCEPT:

• Zener diode: It is a highly doped p - n junction which is not damaged by high reverse current.
• It can operate continuously, without being damaged in the region of reverse background voltage.
• It is represented by

EXPLANATION:

• Zener diode can be used as voltage regulator, voltage clamper and voltage reference. Therefore option 1 is correct.
• A transistor is a device used to amplify electronic signals. Therefore option 2 is incorrect.
• IC or integrated circuit consists of thousands of small resistors, capacitors, and transistors. It can perform as a timer, microprocessor, oscillator, amplifier, etc. Therefore option 3 is incorrect.
• Resistors are used to reduce the flow of current. Therefore option 4 is incorrect.

CONCEPT:

• Zener diodes are normal PN junction diodes operating in a reverse-biased condition.
  • Working of the Zener diode is similar to a PN junction diode in forward biased condition, but the uniqueness lies in the fact that it can also conduct when it is connected in reverse bias above its threshold/breakdown voltage.
  • It is operated in a breakdown region.

• Photo-diode: It is a light-sensing device which is used to sense the intensity of light
  • Some of the examples are the smoke detector, a receiver in tv for converting remote signals, etc.
• Normal P-N junction diode: just like Zener diode when semiconductors of P and N-type doping is combined such devices are called p-n junction diode but unlike Zener diode, this types of diode do not work in reverse bias
• A light-emitting diode (LED): The device which is used to produce the different intensity of light and different colour depending upon the types of mater used in making it is called LED.

Some symbols:

1)     Zener diodes

2)     Normal P-N junction

3)     A light-emitting diode (LED)

4)             Photo-diode

EXPLANATION:

• A Zener diode is used as a voltage regulator in reverse biased mode.
• The breakdown voltage in the Zener diode when connected in the reverse-biased is called Zener voltage.
• This Zener voltage so steady and constant, it has huge applications in circuits, most importantly, voltage regulation.
• From the above explanation, we can see that Zener diode is fabricated by heavily doped p-side and n-side, which help it in operating in reverse bias.

So option 3 is correct.

CONCEPT:

• A photodiode is one type of light detector, used to convert the light into current or voltage.
• The working principle of a photodiode is, when a photon of ample energy strikes the diode, it makes a couple of an electron-hole.
• This mechanism is also called as the photoconductive effect. So option 2 is correct.
• Photoconductive detectors use the increase in electrical conductivity resulting from increase in the number of free carriers generated when photons are absorbed (generation of current)

• User may get confused with the photoelectric effect and photoconductive effect.
• The photoconductive effect is special case of photoelectric effect where the device is reversed biased.

Zener Diode is mostly used as Voltage Regulator.

CONCEPT:

Zener diode: A Semiconductor Diode blocks current in the reverse direction, but will suffer from premature breakdown or damage if the reverse voltage applied across becomes too high.

Zener diode as voltage regulator: The Zener diode is connected with its cathode terminal connected to the positive rail of the DC supply so it is reverse biased and will be operating in its breakdown condition. Resistor R_s is selected so to limit the maximum current flowing in the circuit.

EXPLANATION:

• A Zener diode is used as a voltage regulator in reverse biased mode.
• The breakdown voltage in the Zener diode when connected in the reverse-biased is called Zener voltage. This Zener voltage so steady and constant, it has huge applications in circuits, most importantly, voltage regulation.

So option 3 is correct.

Additional Information

• Half wave rectifier: A half-wave rectifier is only allowing one half-cycle of an AC voltage waveform to pass, blocking the other half-cycle. Half-wave rectifiers are used to convert AC voltage to DC voltage, and only require single diodes to construct.
• Full-wave rectifier: A full-wave rectifier converts both halves of each cycle of an alternating wave (AC signal) into a pulsating DC signal.
• LED: A light-emitting diode is a semiconductor device that emits visible light when an electrical current passes through it.

CONCEPT:

Diode:

• A diode is a semiconductor device that essentially acts as a one-way switch for current.
  • It allows current to flow easily in one direction but severely restricts current from flowing in the opposite direction.

• Forward bias and reverse bias:

EXPLANATION:

Reverse bias:

• When an external voltage (V ) is applied across the diode such that the n-side is positive and the p-side is negative, it is said to be reverse biased. The applied voltage mostly drops across the depletion region.
• The direction of the applied voltage is the same as the direction of barrier potential. As a result, the barrier height increases, and the depletion region widens due to the change in the electric field. Hence, option 1 is correct.

CONCEPT:

• Zener diode: It is a highly doped p - n junction which is not damaged by high reverse current.
• It can operate continuously, without being damaged in the region of reverse background voltage.
• It is represented by

EXPLANATION:

• When a Zener diode is operated in the reverse breakdown region, a voltage across it remains practically constant (equal to the break voltage V_Z)  for a large change in the reverse current.
• Thus based on this fact Zener diode is used as a voltage regulator.

CONCEPT:

• Semiconductor: Semiconductors are the materials that have a conductivity between conductors (generally metals) and non-conductors or insulators (such as ceramics).
• Doping of semiconductor: To improve the electrical properties of semiconductors, the impurities are added to it that is called the doping of semiconductors.

• Diode: A diode is a semiconductor device that essentially acts as a one-way switch for current. It allows current to flow easily in one direction but severely restricts current from flowing in the opposite direction.

EXPLANATION:

• In a P−N junction diode, if the P - region is heavily doped than the N region then, the depletion layer is more on the less doped side.
• Hence, option 2 is correct.

CONCEPT:

Ripple

• ‘Ripple’ is the unwanted AC component remaining when converting the AC voltage waveform into a DC waveform. Even though we try our best to remove all AC components, there is still some small amount left on the output side which pulsates the DC waveform. This undesirable AC component is called a ‘ripple’.

​Ripple factor

• The ripple factor is the ratio between the RMS value of the AC voltage (on the input side) and the DC voltage (on the output side) of the rectifier.

​\(\Rightarrow r=\frac{\sqrt{I_{rms}^{2}-I_{dc}^{2}}}{I_{dc}}\)     -----(1)

CALCULATION:

Given \(I_{rms}=\frac{I_{o}}{\sqrt{2}}\) and \( I_{dc}=\frac{I_{o}}{\pi}\)

• A rectifier is a device that converts an alternating current into a direct current. A p-n junction can be used as a rectifier because it permits current in one direction only.
• A p-n junction can be used as a rectifier because it permits current in one direction only.

By equation 1,

\(\Rightarrow r=\frac{\sqrt{I_{rms}^{2}-I_{dc}^{2}}}{I_{dc}}\)

\(\Rightarrow I_{rms}=\frac{\sqrt{\frac{I_{o}^{2}}{2}-\frac{I_{o}^{2}}{\pi^{2}}}}{\frac{I_{o}}{\pi}}\) = 1.21

• Hence, option 1 is correct.

Additional Information

CONCEPT:

Zener diode:

• A Zener diode is a semiconductor device that allows current to flow either in a forward or reverse direction.
• Since it is highly doped, the depletion layer is very thin and has a high voltage gradient and electric field.

​

EXPLANATION:

• The Zener diode will be operated in the reverse breakdown region so that the voltage will remain constant. Therefore option 3 is correct. 
• In that region, the voltage will be equal to the breakdown voltage and this will make the Zener diode work as a voltage regulator.

Additional Information

Photo diode:

• A photo diode is a semiconductor device that converts light into electrical current.
• It is commonly used in remote controls to detect signals from an infrared (IR) .

Tunnel diode

• A tunnel diode is a highly doped semiconductor diode.
• The p-type and n-type semiconductor is heavily doped in a tunnel diode due to a greater number of impurities. Heavy doping results in a narrow depletion region.
• When compared to a normal p-n junction diode, tunnel diode has a narrow depletion width.
• The Fermi level moves in the conduction band on the n-side and inside the valence band on the p-side.
• Below the Fermi level, all states are filled and above the Fermi level all states are empty

Tunnel diode is represented by the symbol