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

Explanation:

A tunnel diode, also known as an Esaki diode, is a special type of diode that exhibits a unique behavior called negative differential resistance. This characteristic makes it capable of both amplification and oscillation.

Negative Differential Resistance:

In a typical diode, the current increases with an increase in voltage (positive resistance). However, in a tunnel diode, there is a region in its voltage-current characteristic where an increase in voltage leads to a decrease in current. This is called negative differential resistance.

Tunneling Effect:

The negative resistance region is a result of quantum tunneling. As the voltage across the diode increases, electrons overcome a potential barrier by tunneling through it. This tunneling effect causes the current to decrease even as the voltage increases.

Amplification:

The negative resistance property of the tunnel diode allows it to be used for amplification. When biased properly, it can amplify weak signals.

Oscillation:

The negative resistance characteristic also allows the tunnel diode to be used in oscillator circuits. In an oscillator, the diode is combined with other circuit elements to create a feedback loop that sustains oscillations. The tunneling effect helps in achieving the necessary conditions for sustained oscillations.

The Correct option is 2

Concept:

SCR

• A Silicon Controlled Rectifier is a 3-terminal and 4-layer semiconductor current-controlling device. It is mainly used in devices for the control of high power.
• The silicon-controlled rectifier is also sometimes referred to as an SCR diode, 4-layer diode, 4-layer device, or Thyristor.
• 3 terminals- Anode, Cathode & Gate
• Three junctions- J1, J2, J3
• 4 Layers- P, N, P, N

​

Characteristic of SCR:

The Correct option is 4

Concept

Bipolar transistors are basically two types

• NPN bipolar transistors
• PNP bipolar transistors

NPN bipolar transistors

• The NPN transistor consists of two n-type semiconductors that sandwich a p-type semiconductor. Here, electrons are the majority charge carriers, while holes are the minority charge carriers.

​PNP bipolar transistors

• This bipolar PNP junction transistor is formed with three layers of semiconductor material, with two P-type regions sandwiched between one N-type region.

​Equation

Emitter current = collector current + base current

I_E = I_B + I_C

• In a transistor doping level emitter>base>collector

The Correct option is 3

Concept

Zener diode

The Zener diode is a special type of diode that allows the flow of current in the opposite direction of the arrow of the diode. This diode does not conduct until the applied voltage reaches or is greater than the breakdown voltage. This voltage is the “Zener voltage”.

Zener diode as a voltage regulator

Zener Diodes can be used to produce a stabilized output with low ripple under varying load current conditions. By bypassing a small current through the diode from a voltage source, via a suitable current limiting resistor (RS), the Zener diode will conduct sufficient current to maintain a voltage drop of Vout.

 

Biasing of the circuit

1.) Forward biasing

When we apply the external voltage across the semiconductor diode in such a way that the p-side is connected to the positive terminal of the battery and the n-side is connected to the negative terminal, then the semiconductor diode is said to be forward-biased. 

During forward biasing, the ideal value of resistance is zero and the ideal value of conductance is infinite.

The diode is short-circuited under forward bias conditions, hence acting as a closed switch.

The depletion width decrease during the forward bias condition.

2.) Reverse biasing

When we apply the external voltage across the semiconductor diode in such a way that the p-side is connected to the negative terminal of the battery and the n-side is connected to the positive terminal, then the semiconductor diode is said to be reverse-biased. 

During reverse biasing, the ideal value of resistance is infinite and the ideal value of conductance is zero.

The diode is open-circuited under reverse bias conditions, hence acting as an open switch.

The depletion width increases during the reverse bias condition.

The Correct option is 2

Concept:

SCR

• A Silicon Controlled Rectifier is a 3-terminal and 4-layer semiconductor current-controlling device. It is mainly used in devices for the control of high power.
• The silicon-controlled rectifier is also sometimes referred to as an SCR diode, 4-layer diode, 4-layer device, or Thyristor.
• 3 terminals- Anode, Cathode & Gate
• Three junctions- J1, J2, J3
• 4 Layers- P, N, P, N

​

Characteristic of SCR:

The forward voltage at which the current through PN junction starts increasing rapidly is known as knee voltage. The Knee voltage of a crystal diode is approximately equal to barrier potential.

Knee voltage of “germanium” diode is 0.3 volts

Knee voltage of “silicon" diode is 0.7 volts

Zener diode:

• A Zener diode is a heavily doped semiconductor device that is designed to operate in the reverse direction.
• A Zener diode operates just like a normal diode when it is forward-biased.
• When the voltage across the terminals of a Zener diode is reversed and the potential reaches the Zener Voltage (knee voltage), the junction breaks down and the current flows in the reverse direction. This effect is known as the Zener Effect.
• The Zener diode acts as a voltage regulator.

The material which is not a good conductor or a good insulator is called a semiconductor.

For example Silicon, Germanium, etc

Intrinsic semiconductors: Intrinsic semiconductors have equal numbers of electrons and holes. Intrinsic means pure, and without any impurity.

Extrinsic semiconductors: When small amount of impurity is doped in intrinsic semiconductor it is become extrinsic semiconductors.

A superconductor is an element or metallic alloy which, when cooled below a critical temperature of the substance, then it loses all electrical resistance.

• The function of the heat sink in semiconductor devices is to control the temperature rise.
• Heat sinks are either made up of aluminum or copper or any other material, which is a good conductor of heat.
• The heat sink is used in transistors to radiate the excessive heat of the transistor.

• A solar cell is a device that converts photons from the sun (solar light) into electricity. 
• Solar cells are made of semiconductor materials like silicon, cadmium telluride, and copper indium gallium selenide.
• The working principle of solar cells is based on the photovoltaic effect. The photovoltaic effect is the production of electricity by a material when it is exposed to the light. Solar cells convert the sun's energy into electricity.
• The common single junction silicon solar cell can produce a maximum open-circuit voltage of approximately 0.5 to 0.6 volts.

Open-circuit voltage:

• It is maximum open circuit voltage (VOC) available from a solar cell at zero current. The value of open circuit voltage is about 0.57 volts at 25°C
• Open circuit voltage, \({{\rm{V}}_{{\rm{oc}}}} = {{\rm{V}}_{\rm{t}}}\ln \left( {1 + \frac{{{{\rm{J}}_{\rm{L}}}}}{{{{\rm{J}}_{\rm{S}}}}}} \right)\)

Where,

• V_t is temperature equivalent voltage
• J_S is reverse saturation current density  
• J_L is photo current density 

Efficiency:

• Maximum efficiency of practically used solar cells is about 20%
• The highest efficiency of solar cell achieved till date is 46%
• The efficiency of a solar cell is determined as the fraction of incident power which is converted to electricity and is defined as:
• \(\eta = \frac{{({V_{oc}}{I_{SC}})\left( {F.F} \right)}}{{{P_{in}}}}\)

Where:

• Voc is the open-circuit voltage
• Isc is the short-circuit current
• FF is the fill factor
• η is the efficiency

In Transistors biasing is done to keep stable DC operating conditions needed for its functioning as an amplifier. A properly biased transistor must have its Q-point (DC operating parameters like IC and VCE) at the centre of saturation mode and cut-off mode i.e. active mode.

In the active mode of transistor operation, the base-emitter junction is forward biased and the base-collector junction is reverse biased.

Important Point:

Different modes of BJT operations

Type of semiconductors:

1.) p-type semiconductor

• An acceptor is a dopant atom that when added to a semiconductor can form a p-type region.
• These atoms have electrons less than four in their outermost shell, and hence they accept electrons from nearby atoms.
• Since the trivalent atoms, i.e. dopant having a valency of 3 i.e. an element whose each atom has 3 valence electrons is called a Trivalent impurity. For example Indium, Gallium, Aluminum, Boron, etc.

2.) n-type semiconductor

• A donor is a dopant atom that when added to a semiconductor can form a p-type region.
• These atoms have electrons greater than four in their outermost shell, and hence they donate electrons from nearby atoms.
• Since the pentavalent atoms, i.e. dopants having a valency of 5 i.e. an element whose each atom has 5 valence electrons is called a Pentavalent impurity. For example Phosphorus, Arsenic, Antimony, etc.

Concept:

In a transistor, emitter current (I_e)can be calculated as

I_e = I_b + I_c

Where,

I_b = base current

I_c = collector current

Note:

Common base current gain (α) is defined as the ratio of collector current to emitter current of a transistor.

\(\alpha = \frac{{{I_c}}}{{{I_e}}}\)

\(\alpha = \frac{\beta }{{\beta + 1}}\)

Common emitter current gain (β) is defined as the ratio of collector current to base current transistor.

\(\beta = \frac{{{I_c}}}{{{I_b}}}\)

\(\beta = \frac{\alpha }{{1 - \alpha }}\)

Calculation:

I_C = 4.5 mA,

I_b = 20 μA = 0.02 mA

I_e = 4.5 + 0.02

I_e = 4.52 mA

The correct answer is option 3

CONCEPT:

• The material which is not a good conductor or a good insulator is called a semiconductor.
• For example Silicon
• The charge carriers which are present in more quantity in a semiconductor compared to other particles are called the majority charge carrier.

• The impurity atoms added are called dopants and semiconductors doped with the impurity atoms are called extrinsic or doped semiconductors.
• The pure form of a semiconductor is called an intrinsic semiconductor.

There are two types of semiconductors:

P-type semiconductor:

• The semiconductor having holes as majority charge carriers and electrons as a minority charge carrier is called a P-type semiconductor.
• When a trivalent impurity is doped in intrinsic semiconductors then we got P-type semiconductors. For Example: gallium, indium 

N-type semiconductor:

• The semiconductor having electrons as majority charge carriers and holes as a minority charge carrier are called N-type semiconductors.
• When a pentavalent impurity is doped in intrinsic semiconductors then we got N-type semiconductors. For Example: Arsenic

EXPLANATION: