PN Junction Diodes
P-N Junction and Semiconductor Devices
Page 2: Formation of P-N Junction
Definition of Junction
Junction refers to a point where two or more things are joined.
Example: Railway junction where tracks meet.
P-N Junction Formation
Formed by joining n-type and p-type semiconductors.
Acts as a boundary between the two types of semiconductors.
Creates a diode, a fundamental semiconductor device.
Page 4: Discovery and Importance
Discovery
Discovered by American physicist Russel Ohi at Bell Laboratories.
Significance
Fundamental building block for various semiconductor devices:
Transistors
Solar cells
Light-emitting diodes (LEDs)
Integrated circuits
Page 6-7: Zero Bias P-N Junction
Definition
A p-n junction with no external voltage applied.
Also known as unbiased p-n junction.
Charge Carrier Concentration
N-type has a high concentration of free electrons.
P-type has a low concentration of free electrons.
Electrons move from n-side to p-side due to concentration gradient.
Holes move from p-side to n-side similarly.
Page 8-10: Formation of Ions and Barrier Voltage
Ion Formation
Free electrons crossing to p-side create negative ions (acceptors).
Electrons leaving n-side create positive ions (donors).
Barrier Voltage
Net positive charge at n-side and net negative charge at p-side.
Prevents further flow of charge carriers across the junction.
Barrier voltage depends on doping, temperature, and material type.
Page 12-14: Depletion Region
Definition
Region near the junction with reduced charge carriers.
Acts as a wall preventing further flow of electrons and holes.
Width Dependency
Width varies with impurity levels: wider in lightly doped semiconductors.
Page 15-19: P-N Junction Diode
Definition
A two-terminal device allowing current in one direction.
Biasing
Forward bias allows current flow; reverse bias blocks it.
Page 20-28: Forward Biasing
Process
Positive terminal connected to p-type, negative to n-type.
Current flows when voltage exceeds cut-in voltage (0.7V for silicon, 0.3V for germanium).
Current Flow
Free electrons and holes recombine, reducing the depletion region.
Page 29-33: Reverse Biasing
Process
Positive terminal connected to n-type, negative to p-type.
Blocks majority carriers; allows minority carriers to flow.
Current Characteristics
Reverse saturation current is small and temperature-dependent.
Page 34-40: V-I Characteristics
Ideal Diode Equation
Describes the relationship between current and voltage in a diode.
Reverse Characteristics
Reverse saturation current remains constant until breakdown occurs.
Page 42-46: Diode Resistance
Types of Resistance
Static (DC) resistance: Ratio of DC voltage to current.
Dynamic (AC) resistance: Ratio of change in voltage to change in current.
Silicon vs. Germanium Diodes
Silicon preferred for higher temperature applications.
Different forward bias voltages for silicon (0.7V) and germanium (0.3V).
Page 47-52: Breakdown in Diodes
Types of Breakdown
Avalanche Breakdown: Occurs at high reverse voltage; can damage the diode.
Zener Breakdown: Occurs at low reverse voltage; used in zener diodes.
Page 53-58: Zener Diode
Definition
Operates in reverse breakdown region; allows current in both directions.
Applications
Voltage regulation, protection circuits, and more.
Page 60-66: Photodiode
Definition
Converts light energy into electric current; operates in reverse bias.
Applications
Used in light detection and solar cells.
Page 67-72: Light Emitting Diodes (LEDs)
Definition
Emits light when forward biased; converts electrical energy into light energy.
Color Determination
Depends on the material used; different materials emit different colors.
Page 74-83: Applications of P-N Junction Diode
Rectification
Converts AC to DC using half-wave and full-wave rectifiers.
Types of Rectifiers
Half-wave rectifier: Allows one half-cycle of AC.
Full-wave rectifier: Converts both half-cycles into DC.
Page 85: Example Problem
Calculation
Given load resistance and voltage, calculate peak, rms, and average current, and efficiency of