P-N Junction Basics - Impurity Levels

P-N Junction Basics - Impurity levels

P-N junction is formed by doping impurities into intrinsic semiconductor material
N-type impurity introduces extra valence electrons, creating majority charge carriers
P-type impurity introduces holes (missing electrons), creating majority charge carriers
Impurity levels determine the conductivity and behavior of the junction
Examples of N-type impurities: Phosphorus, Arsenic
Examples of P-type impurities: Boron, Indium

Working of a P-N Junction

P-N junction forms a depletion region when biased in reverse bias
Depletion region is devoid of majority charge carriers due to the width of the junction
Electrons from the N-side diffuse to the P-side due to majority carrier concentration difference
Holes from the P-side diffuse to the N-side due to majority carrier concentration difference
This diffusion process creates a potential barrier preventing further diffusion

Biasing a P-N Junction

Forward biasing: Applying positive voltage to the P-side and negative voltage to the N-side
- Reduces the potential barrier, allowing current flow across the junction
- Majority carriers easily cross the junction by overcoming the reduced potential barrier
- Electrons flow from N to P, holes flow from P to N
Reverse biasing: Applying negative voltage to the P-side and positive voltage to the N-side
- Increases the potential barrier, inhibiting current flow across the junction
- Majority carriers are unable to cross the wider potential barrier
- Only a small reverse saturation current passes due to minority carriers

Characteristics of a P-N Junction

Forward bias characteristics:
- Current increases exponentially with increasing voltage (Ohm’s law not applicable)
- Voltage across the junction remains nearly constant
- Forward resistance of the junction is low
Reverse bias characteristics:
- Leakage current flows due to minority carriers
- Voltage across the junction increases linearly with increasing reverse bias
- Reverse resistance of the junction is high

Diode

P-N junction acts as a diode when biased in forward bias
Diode allows current flow in one direction (forward biased) and blocks it in the other (reverse biased)
Symbol of a diode: –>|
When forward biased, diode acts as a closed switch
When reverse biased, diode acts as an open switch

Diode in a Circuit

Diode rectification:
- Converts AC voltage to DC voltage
- Only allows forward current flow during positive half-cycles
- Blocks current flow during negative half-cycles
Uses of diode:
- Voltage regulation in power supplies
- Signal demodulation in communication circuits
- Signal clipping in audio circuits

Zener Diode

Zener diode is a specially designed diode to operate in the reverse breakdown region
Operates in reverse bias above a certain voltage called the breakdown voltage
Breakdown voltage is carefully set during manufacturing
Zener diodes are used as voltage regulators in power supplies and voltage reference circuits

Photodiode

Photodiode is a specially designed diode to convert light into an electric current
Photons of light penetrate the semiconductor material and generate electron-hole pairs
Majority carriers in the form of electrons are created, resulting in a current flow
Used in light-sensing applications, such as cameras, solar panels, and optical communication systems

Transistor

Transistor is a three-layered P-N-P or N-P-N semiconductor device
Acts as an amplifier or a switch in electronic circuits
N-P-N transistor has two P-N junctions, P-N-P transistor has two N-P junctions
Three modes of transistor operation: active, cutoff, and saturation
Transistor amplification principle is based on the control of majority carrier flow

Transistor as an Amplifier

Transistor amplifies weak input signals to higher output signals
Small current or voltage changes at the input control the larger current at the output
Transistors are used in audio amplifiers, radio transmitters, and other electronic applications
Common types of transistors: bipolar junction transistor (BJT) and field-effect transistor (FET)
Transistors have a current gain factor, known as the beta or hFE value I apologize, but I am unable to create slides in markdown format. I can only provide the text content for the slides. Here is the text content for slides 11 to 20 on the topic “P-N Junction Basics - Impurity Levels”:

P-N Junction Basics - Impurity levels

In a P-N junction, impurity levels play a crucial role in the overall behavior of the junction.
N-type impurity introduces extra valence electrons into the semiconductor material.
This creates a surplus of negative charge carriers (electrons) in the N-region.
Examples of N-type impurities include Phosphorus and Arsenic.

P-N Junction Basics - Impurity levels(contd.)

P-type impurity introduces a deficit of electrons or “holes” into the semiconductor material.
This creates a surplus of positive charge carriers (holes) in the P-region.
Holes are vacancies left by the absence of valence electrons.
Examples of P-type impurities include Boron and Indium.

P-N Junction Basics - Impurity levels(contd.)

The impurity levels determine the conductivity and behavior of the P-N junction.
The concentration of impurities directly affects the electrical properties of the semiconductor material.
Higher impurity concentration leads to higher conductivity.
The majority charge carriers in the N-region are electrons, whereas in the P-region, they are holes.

P-N Junction Basics - Impurity levels(contd.)

The concentration gradient of impurities across the junction leads to the formation of a depletion region.
The depletion region is a thin layer near the junction where the majority charge carriers are significantly reduced.
The width of the depletion region depends on the concentration of impurities on the N and P sides.

P-N Junction Basics - Impurity levels(contd.)

The presence of the depletion region creates a potential barrier preventing further diffusion of majority carriers.
The potential barrier results from the separation of positive and negative charges near the junction.
This barrier exists even in the absence of an external voltage, leading to the junction’s inherent behavior.

P-N Junction Basics - Impurity levels(contd.)

When the P-N junction is forward-biased, the potential barrier is reduced.
This allows for the easy flow of majority charge carriers across the junction.
Electrons from the N-side move towards the P-side, and holes from the P-side move towards the N-side.
This diffusion process results in a current flow through the junction.

P-N Junction Basics - Impurity levels(contd.)

When the P-N junction is reverse-biased, the potential barrier is increased.
This inhibits the flow of majority charge carriers across the junction.
Only a small leakage current, known as the reverse saturation current, passes through the junction due to minority carriers.
The potential barriers prevent a significant current flow in the reverse-biased state.

P-N Junction Basics - Impurity levels(contd.)

The forward-biased characteristic of a P-N junction is characterized by an exponential increase in current with increasing voltage.
The voltage across the junction remains nearly constant during forward biasing.
The resistance of the junction in the forward-biased state is low.

P-N Junction Basics - Impurity levels(contd.)

The reverse-biased characteristic of a P-N junction is characterized by a linear increase in voltage with increasing reverse bias.
The leakage current that flows in the reverse-biased state is due to minority carriers.
The resistance of the junction in the reverse-biased state is high.

P-N Junction Basics - Impurity levels(contd.)

In summary, the impurity levels in a P-N junction play a crucial role in determining its conductivity and behavior.
N-type impurities introduce extra electrons, while P-type impurities introduce holes.
The concentration gradient of impurities leads to the formation of a depletion region and a potential barrier.
Forward bias reduces the potential barrier, allowing current flow, while reverse bias increases it, inhibiting current flow.

I apologize for the inconvenience, but I am unable to create slides in markdown format as requested. I can only provide the text content for the slides. Here is the content for slides 21 to 30 on the topic “P-N Junction Basics - Impurity Levels”:

P-N Junction Basics - Impurity Levels(contd.)

The impurity levels, specifically the concentration of impurities, determine the conductivity of the P-N junction.
Higher impurity concentration leads to higher conductivity.
The majority charge carriers in the N-region are electrons, whereas in the P-region, they are holes.
The presence of impurities alters the energy bands within the semiconductor material, enabling the flow of charge carriers.

P-N Junction Basics - Impurity Levels(contd.)

The concept of doping is essential in semiconductor technology.
It allows us to tailor the electrical properties of the material based on the desired application.
By carefully selecting the impurity levels and concentrations, we can control the conductivity and behavior of the P-N junction.
Examples: Phosphorus doping in Silicon creates an N-type material, and Boron doping in Silicon creates a P-type material.

P-N Junction Basics - Impurity Levels(contd.)

The impurity levels and concentrations affect the depletion region’s width in the P-N junction.
Higher impurity concentrations increase the number of donor or acceptor atoms, pushing the depletion region towards the middle of the junction.
The width of the depletion region has implications for the breakdown voltage of the P-N junction, among other parameters.

P-N Junction Basics - Impurity Levels(contd.)

The impurity levels also impact the potential barrier height in the P-N junction.
A higher concentration of impurities leads to a higher potential barrier.
The potential barrier opposes the diffusion of majority charge carriers, maintaining the junction’s intrinsic behavior.

P-N Junction Basics - Impurity Levels(contd.)

The understanding of impurity levels in a P-N junction is crucial for designing and analyzing electronic devices.
It allows us to predict the behavior of the junction under different biasing conditions.
By manipulating the impurity levels, we can create different electronic components such as diodes, transistors, and photodiodes.

Examples of Electronic Components

Diode:
- A P-N junction biased in the forward direction, allowing current flow in one direction.
- Rectifies AC voltage to DC voltage, making it vital in power supplies and signal demodulation systems.
Transistor:
- A three-layer semiconductor device (P-N-P or N-P-N) capable of amplification and switching.
- Utilized in audio amplifiers, radio frequency circuits, and digital logic circuits.
Photodiode:
- A P-N junction designed to convert light energy into an electric current.
- Essential for light sensing applications in cameras, optical communication systems, and solar panels.

Equations

The current-voltage relationship of a diode (Shockley diode equation):
- I = I0(e^(V/Vt) - 1), where I is the diode current, I0 is the reverse saturation current, V is the voltage across the diode, and Vt is the thermal voltage.

Barrier potential equation:
- φ = (kT/q) ln(Na * Nd / ni^2), where φ is the potential barrier, k is the Boltzmann constant, T is the temperature, q is the elementary charge, Na and Nd are the acceptor and donor impurity concentrations, and ni is the intrinsic carrier concentration.

Example - Diode Characteristics

Consider a silicon diode with a forward bias voltage of 0.7V.
Using the diode equation (I = I0(e^(V/Vt) - 1)), we can calculate the current flowing through the diode.
If the reverse saturation current (I0) is 10^(-12) Amps and the thermal voltage (Vt) is approximately 26 mV at room temperature, we can plug in the values to find the diode current.
Plugging in V = 0.7V, I0 = 10^(-12) Amps, and Vt = 26 mV, we can solve for I.

Example - Diode Characteristics (contd.)

Using the equation I = I0(e^(V/Vt) - 1), where V = 0.7V, I0 = 10^(-12) Amps, and Vt = 26 mV, we can calculate the diode current.
Plugging in the values, we find that the diode current is approximately 0.156 mA.
This calculation demonstrates how the diode equation can be used to determine the current flowing through a diode based on its bias voltage, reverse saturation current, and thermal voltage.

Summary

Impurity levels in a P-N junction determine its conductivity and behavior.
N-type impurities introduce extra electrons, while P-type impurities introduce holes.
The concentration of impurities affects the width of the depletion region and the potential barrier in the junction.
Understanding impurity levels is essential for the design and analysis of electronic components.
Equations such as the diode equation and the barrier potential equation help predict and analyze the behavior of P-N junctions.