Podcast
Questions and Answers
What type of doped semiconductor contains negatively charged electrons as the majority charge carriers?
What type of doped semiconductor contains negatively charged electrons as the majority charge carriers?
What is the role of donor impurities in n-type semiconductors?
What is the role of donor impurities in n-type semiconductors?
What happens during reverse bias in a diode?
What happens during reverse bias in a diode?
Which type of charge carrier is predominant in a p-type semiconductor?
Which type of charge carrier is predominant in a p-type semiconductor?
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Which of the following materials is typically used as a dopant for n-type semiconductors?
Which of the following materials is typically used as a dopant for n-type semiconductors?
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When a diode is forward biased, which terminal is connected to the positive voltage?
When a diode is forward biased, which terminal is connected to the positive voltage?
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What is the main purpose of a diode in electronic circuits?
What is the main purpose of a diode in electronic circuits?
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In the context of pn-junctions, which explanation describes the term 'depletion region'?
In the context of pn-junctions, which explanation describes the term 'depletion region'?
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What is the primary function of a diode in electronic circuits?
What is the primary function of a diode in electronic circuits?
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Which characteristic identifies the functioning state of a diode?
Which characteristic identifies the functioning state of a diode?
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Which of the following materials is predominantly used in today's integrated circuit technology?
Which of the following materials is predominantly used in today's integrated circuit technology?
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What is formed when two valence electrons from different silicon atoms bond?
What is formed when two valence electrons from different silicon atoms bond?
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What does the 'pn junction' refer to in a diode?
What does the 'pn junction' refer to in a diode?
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In a crystal of intrinsic semiconductor, what holds the silicon atoms together?
In a crystal of intrinsic semiconductor, what holds the silicon atoms together?
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What type of semiconductor is created when carriers of one kind predominate?
What type of semiconductor is created when carriers of one kind predominate?
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Which statement best describes free electrons in a semiconductor?
Which statement best describes free electrons in a semiconductor?
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What type of current is typically used as the input for a half-wave rectifier?
What type of current is typically used as the input for a half-wave rectifier?
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What produces light in a Light Emitting Diode when current flows?
What produces light in a Light Emitting Diode when current flows?
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Why is the output voltage slightly less than the input voltage in a rectifier?
Why is the output voltage slightly less than the input voltage in a rectifier?
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What is the typical voltage requirement for connecting a standard LED?
What is the typical voltage requirement for connecting a standard LED?
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Which statement describes how the frequency characteristic of light emitted by an LED is determined?
Which statement describes how the frequency characteristic of light emitted by an LED is determined?
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What is the purpose of using a resistor when connecting an LED to a power source?
What is the purpose of using a resistor when connecting an LED to a power source?
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What is the approximate resistance value suggested to prevent overloading when using a standard LED?
What is the approximate resistance value suggested to prevent overloading when using a standard LED?
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What technology is referred to by the acronym 'LED'?
What technology is referred to by the acronym 'LED'?
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Study Notes
International & Access Foundation Programmes
- The presentation covers Engineering Module - Semester 1, Electronic & Electrical Engineering.
- The specific topic for this part is Diodes & LED's.
- The presenter is Dr. Nevan Bermingham.
Introduction to Diodes
- A diode is the simplest and most fundamental non-linear circuit component.
- Like a resistor, it has two terminals.
- Unlike a resistor, a diode has non-linear current-voltage characteristics.
- Diodes are commonly used in rectifiers.
Diode Physical Structure
- The most important region within a diode is the pn-junction.
- This is the boundary between the n-type and p-type semiconductors.
- The presentation includes a diagram illustrating this structure.
Symbol and Characteristic for the Ideal Diode
- The arrow-like symbol indicates the direction of current flow.
- In forward bias (voltage <0), current ( i ) =0.
- In reverse bias (voltage > 0), current ( i ) =0.
Characteristics
- The arrow on the circuit symbol shows current flow direction.
- Diodes allow current to flow in one direction only.
- Forward bias turns the diode on.
- Reverse bias turns the diode off.
Revision: Intrinsic Semiconductors
- A pure crystal with a regular lattice structure is an intrinsic semiconductor.
- Modern IC technology mostly relies on silicon.
- Germanium was previously used in some applications.
- Gallium arsenide is used in microwave circuits.
Intrinsic Semiconductor
- Two-dimensional representation shows the silicon crystal.
- Inner core of silicon atoms' positive charges are neutralized by four valence electrons.
- All bonds are intact; no free electrons exist for current conduction.
Intrinsic Semiconductor Review
- Terms: Valence electron: each silicon atom has four valence electrons.
- Terms: Covalent bond: two valence electrons from different silicon atoms form a covalent bond.
- A free electron is a negative charge, and a hole is a positive charge. They both contribute to electricity in circuits.
- Doped semiconductors: materials where one type of carrier (electron or hole) predominates.
- Two types of doped semiconductors: p-type and n-type.
- Doped semiconductors have higher conductivity than intrinsic ones.
Extrinsic Carriers
- Two types of dopants: donors (n-type) and acceptors (p-type).
- Donors contribute electrons, becoming positive ions.
- Acceptors contribute holes, becoming negative ions.
N-Type Semiconductor
- Doped silicon where majority charge carriers are negatively charged electrons.
- Pentavalent impurity atoms (donors) are added during doping.
- This type of semiconductor is called n-type.
P-Type Semiconductor
- Doped silicon where majority charge carriers are positively charged holes.
- Trivalent impurity atoms (acceptors) are added during doping.
- This type of semiconductor is called p-type.
Diode Physical Structure
- The pn-junction (boundary between n-type and p-type semiconductors) is the most important region within a diode.
P Types & N Types
- Diagrams illustrate the structure and the differences between P and N type silicon, showing missing electrons (holes) in P-type, and extra electrons in N-type.
The Diode
- Cross-section of p–n junction in an IC process.
- N-type region is doped with donor impurities (e.g., phosphorus, arsenic).
- P-type region is doped with acceptor impurities (e.g., boron).
The Diode – Simplified Structure
- Diagram illustrates a simplified one-dimensional representation of the pn-junction.
The Diode Potential Barrier or Depletion Zone
- The p-side depletion region is negatively charged due to recombined holes with electrons from the n-side.
- The n-side depletion region is positively charged due to recombined electrons with holes from the p-side.
The PN Junction
- Diagrams show how free electrons diffuse to the p-side, creating a depletion region.
- A barrier potential is formed due to charges on either side of the junction.
Forward Bias
- DC voltage applied with positive terminal to the p-region and negative terminal to the n region.
- This condition permits current flow through the p-n junction of a diode.
- Diagram illustrates the forward biased connection.
Reverse Bias
- DC voltage applied with negative terminal to the p-region and positive terminal to the n region.
- This condition widens the depletion region, preventing current flow.
- Diagram illustrates the reverse biased connection showing the widened depletion region.
Diode Current Flow Characteristics
- Graph of diode current versus voltage displaying forward and reverse bias regions.
- Shows the characteristic curve of a diode.
The Application of Diode Circuits
- Circuits using diodes: Rectifiers (half-wave and full-wave), voltage regulators, and limiters.
What is the output of this circuit?
- Shows the input waveform (alternating current) and the expected output waveform (half-wave rectified).
Half-Wave Rectifier
- Circuit diagram, input waveform, and output waveform (half-wave rectified) demonstrating how a diode circuit can turn AC into pulsed DC.
What about this one?
- Circuit diagram of a full-wave rectifier using a transformer and two diodes. Diagram of AC input and expected output.
Full-Wave Rectifier
- Circuit diagram showing the configuration and operation of a full-wave rectifier circuit.
- Shows the input waveform and expected output.
Why is the Output slightly less tan the input?
- Diagram explains why a full-wave rectifier's output voltage is smaller than the peak input voltage.
LED - Light emitting Diode
- This is a diode that gives off light of one color when in forward bias.
- Its core is a semiconductor material with polarity. Diagram of an LED and its parts.
Inside a Light Emitting Diode
- Diagram illustrating the internal structure of an LED, including the diode, transparent plastic case, and terminal pins.
Structure
- A diagram illustrates the internal layers of an LED. Key components labeled.
High Power LED's
- Diagram shows a high-power LED in a common package.
LED Lighting Efficiency
- The diagram illustrates various types of light sources.
- A table providing a comparison of different lighting options by luminescence(brightness), Watts/Viribright, CFL Watts, and incandescent Watts.
LED Lighting Efficiency - Costs
- Table compares the costs of incandescent, CFL, and LED lighting over 25 years.
- Data includes cost per bulb, lifespan, bulbs needed over 25 years, electricity cost, total cost over 25 years.
LED: How It Works
- Illustration shows negatively charged electrons and positively charged holes flowing in different directions across a diode.
LED: How It Works
- Each recombination of a negative and positive charge releases a quantum of electromagnetic energy as a photon of light.
- The frequency (color) of the light depends on the semiconductor material.
Kinds of LEDs
- A collection of different types of LEDs including various shapes and sizes are displayed. LEDs are useful in a variety of applications.
Numeric Displays
- 16-segment alphanumeric displays are available in Green, Yellow, or Red.
- Each segment in the 18-pin package consists of one LED.
Numeric Displays
- A diagram depicts a numeric display.
- The diagram identifies segments (e.g., a, b, c, d, e, f, g, dp) on the display.
How to Connect a LED
- LED requires usually1.5-2.5V and 10mA of current.
- Using a resistor is crucial for preventing overloading (e.g., a 470 Ω resistor.)
Laser LED's
- Diagram illustrating the structures of Laser LEDs including the highly reflective ends and the partially reflective ends to create light beams.
Laser LED's – Relative Size
- An image compares a laser LED with an insect, highlighting its small size.
Laser LED's - Fibre Optics
- Illustration shows a fiber optic cable, its components, and a text describing the use of the technology in telecommunication.
Tri Colour LED's
- Tri-color LEDs are typically red, blue, and green LEDs in one package.
- They can create any color of light by combining the three colors.
- Diagrams show the LEDs.
Any Questions?
- A slide with a university logo and a question mark. Commonly used at the conclusion of a presentation.
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Description
Test your knowledge on semiconductor types, charge carriers, and diode functionalities. This quiz covers essential concepts related to n-type and p-type semiconductors, as well as the role of donor impurities and the behavior of diodes in electronic circuits.
