Semiconductors

Step 1: Define intrinsic semiconductors. In intrinsic semiconductors, the conductivity is due to the breaking of covalent bonds, creating free electrons and holes.
Step 2: Conclusion. Thus, when conductivity is due to the breaking up of covalent bonds, the semiconductor is intrinsic.

Step 1: P-type semiconductor characteristics. In a P-type semiconductor, the acceptor impurities are atoms with one less electron than the semiconductor atoms, and they create holes just below the valence band.
Step 2: Conclusion. Thus, in a P-type semiconductor, the acceptor impurity is located just below the valence band.

Step 1: Analyzing the truth table.
The given truth table shows the behavior of a NOR gate, as it outputs 1 only when both inputs are 0.

Step 2: Conclusion.
Thus, the correct answer is option (A).

Final Answer:

Step 1: Boolean identity.
In Boolean algebra, represents the AND operation, while the options provided represent different logical expressions.

Step 2: Conclusion.
The correct answer is option (D).

Final Answer:

Step 1: Analyzing the circuits.
In circuits 2 and 3, the two P-N junctions are connected such that the potential drop across each is equal. In circuit 1, the two P-N junctions are connected with a different potential configuration.

Step 2: Conclusion.
Therefore, the correct answer is option (A).

Final Answer:

Step 1: Zener Diode Characteristics.
Zener diodes exhibit a negative temperature coefficient for their breakdown voltage. As the temperature increases, the breakdown voltage decreases.

Step 2: Conclusion.
Therefore, the correct answer is option (A).

Final Answer:

Step 1: Current through the components.
When the conductor and semiconductor are in parallel, the current through each depends on the resistance of the material. When the voltage is increased, the current will increase, but the ratio of currents remains the same.

Step 2: Conclusion.
Thus, the correct answer is option (C).

Final Answer:

Step 1: Recall expression of reverse saturation current.
Reverse saturation current is mainly due to minority carriers:

Step 2: Identify dependencies.
From this expression, depends on:
(i) doping concentrations
(ii) diffusion constants
(iii) diffusion lengths
(iv) intrinsic concentration
Step 3: Role of temperature.
strongly increases with temperature, so increases sharply with temperature.
Step 4: Match with option.
Thus, it depends on doping concentration, diffusion length and temperature.
Final Answer:

Step 1: Identify the configuration.
The non-inverting terminal of op-amp is grounded, and input is applied through a resistor to the inverting terminal.
So the circuit is an inverting amplifier.
Step 2: Write gain formula for inverting amplifier.

Step 3: Substitute resistor values from diagram.
From figure:

Step 4: Calculate output.

Final Answer:

Step 1: Understand donor level position.
A donor level lies just below the conduction band and donates electrons easily to the conduction band.
Step 2: Effect of donor impurity.
When electrons are donated, the conduction band gets extra electrons, increasing conductivity.
Step 3: Identify majority charge carriers.
Since electrons become majority carriers, the material becomes an n-type semiconductor.
Step 4: Match with option.
Thus, correct option is (D).
Final Answer:

Step 1: Use formula for built-in (contact) potential.

Step 2: Substitute given values.

Step 3: Compute the ratio inside log.


Step 4: Final expression.

Final Answer:

Step 1: Use relation between electric field and breakdown voltage.
Electric field in depletion region:

Step 2: Substitute given values.

Step 3: Calculate breakdown voltage across depletion layer.

Step 4: Match with option.
Thus, reverse biased potential required is .
Final Answer:

Step 1: Use conductivity of intrinsic semiconductor.
Current density:
where conductivity:
Step 2: Calculate electric field.
Thickness .
Step 3: Calculate conductivity.
Given:
, .
Step 4: Find current density.
Step 5: Find current.
Area .
Final Answer:

Step 1: Use Child’s law for space charge limited current.
For diode in space charge limited region:
Step 2: Apply ratio form.
Step 3: Substitute values.
Step 4: Simplify.
So,
Final Answer:

Step 1: Understand Zener diode operation.
A Zener diode is a heavily doped p-n junction diode designed to work in reverse breakdown region.
Step 2: Key property of Zener diode.
In breakdown region, Zener diode maintains a nearly constant voltage across it even if current changes.
Step 3: Application in circuits.
Because of this constant voltage property, it is used as a voltage regulator.
Voltage regulation means stabilisation of voltage.
Final Answer:

The current gain is defined as , where is the change in collector current and is the change in base current. Using the given values, the current gain is calculated to be 100.

Step 2: Conclusion.
The current gain is 100, corresponding to option (b).

In a full-wave rectifier, the negative part of the input signal is inverted, resulting in a waveform that is always positive and resembles a square wave.

Step 2: Conclusion.
The output waveform of a full-wave rectifier is square, corresponding to option (c).

In a common emitter amplifier, the input signal is typically applied across the base and emitter of the transistor. The current passing through the transistor is found to be 2A.

Step 2: Conclusion.
The input signal in a common emitter amplifier is applied across , corresponding to option (b).

In a p-n junction diode, when the diode is forward biased, the current flows easily and the voltage across the resistor is equal to the applied voltage . When reverse biased, the current is minimal, and the voltage across is near zero.

Step 2: Conclusion.
In forward bias, the voltage across is equal to , corresponding to option (a).

Step 1: Formula for conductivity.
The electrical conductivity of a material is given by the formula: where is the charge of an electron, and are the electron and hole densities, and and are their mobilities.

Step 2: Calculations.
Substitute the given values to calculate the conductivity of germanium. The answer is 2.12 S/m.

The separation between the conduction band and the valence band in semiconductors typically lies around 1 eV, which is the energy required for an electron to jump from the valence band to the conduction band.

The current through the Zener diode can be found using Ohm's law by considering the voltage across the diode and the resistances in the circuit. The Zener diode maintains a constant voltage across it, allowing calculation of the current.

The resistance of the germanium junction diode is calculated from the slope of the curve. Given the voltage and current values at the knee of the curve, we can compute the resistance using Ohm's law: Where and .

The output of the logic circuit depends on the combination of logic gates. By analyzing the circuit diagram, we can derive the Boolean expression for the output.

The addition of impurities to a metal disrupts the regular lattice structure, increasing resistance and reducing both electrical and thermal conductivities.

An n-type semiconductor is formed by doping a semiconductor with elements that donate electrons, making it negatively charged. However, its charge may change based on the impurity added.

Step 1: Analyze the combination of gates.
The combination of the gates shown in the figure corresponds to an AND gate.
Step 2: Conclusion.
Thus, the combination of gates results in an AND gate.
Final Answer:

Step 1: Understand the transistor switch behavior.
To use a transistor as a switch, it needs to be in the saturation region, which is region (III) in the transfer characteristic curve.
Step 2: Conclusion.
Thus, the transistor is used in region (III) for switching applications.
Final Answer:

Step 1: The voltage amplification of a common emitter amplifier is given by the formula , where is the load resistance and is the internal resistance of the transistor.
Step 2: Given and , the voltage amplification is: Since the amplifier gain is usually positive, the voltage amplification comes out to be 460.

Final Answer:

Step 1: The current flowing through the diode depends on the voltage across the junction. Since the diode is ideal, it will conduct current when the voltage exceeds the threshold value, and the current is determined by Ohm's law.
Step 2: Using the given parameters of the circuit, the current flowing through AB is calculated to be .

Final Answer:

Step 1: Relation between collector current, base current, and amplification factor.
The collector current is related to the base current and amplification factor by the formula: Step 2: Calculation of .
The emitter current is given by: Substituting the values: This gives mA. Now, we calculate :
Final Answer:

After analyzing the logic gates, it is determined that the output of gate C is 1. The specific configuration and truth table of the gate are used to arrive at this conclusion.
Final Answer:

For semiconductor diodes, reverse saturation current approximately doubles for every rise in temperature.