• In forward bias, the depletion region narrows, allowing current to flow.
• In reverse bias, the depletion region widens, preventing significant current flow.

P-type semiconductor:

• Doped with acceptor impurities (e.g., boron in silicon).
• Has an abundance of holes, which are positive charge carriers.
• Holes are the majority carriers, while electrons are the minority carriers.

N-type semiconductor:

• Doped with donor impurities (e.g., phosphorus in silicon).
• Has an abundance of electrons, which are negative charge carriers.
• Electrons are the majority carriers, while holes are the minority carriers.

• Primary charge carriers: Electrons, which are introduced by doping the semiconductor with donor impurities (e.g., phosphorus).

• Primary charge carriers: Holes, which are introduced by doping the semiconductor with acceptor impurities (e.g., boron).

• Operation: Zener diodes are designed to operate in reverse bias and are used primarily for voltage regulation. They maintain a constant voltage when the reverse voltage exceeds the breakdown voltage.
• Applications: Zener diodes are commonly used in power supply circuits for voltage stabilization and as reference voltages.

• Operation: Schottky diodes are designed to have a low forward voltage drop (typically 0.2-0.3V) and fast switching capabilities. They do not have a typical p-n junction but instead form a metal-semiconductor junction.
• Applications: Schottky diodes are widely used in high-speed switching applications, power rectifiers, and RF circuits where fast operation and low power loss are required.

• Light meters: Photodiodes are used to measure light intensity in devices such as cameras and industrial light sensors.
• Optical communication systems: In fiber-optic communication systems, photodiodes are used to convert optical signals into electrical signals.
• Solar cells: Photodiodes are used in solar cells to convert light energy into electrical energy for power generation.

• Indicators: LEDs are widely used in electronic devices as visual indicators, showing operational status (on/off).
• Displays: LEDs are used in displays for televisions, computer screens, and digital billboards.
• General lighting: LEDs are used in residential and commercial lighting due to their energy efficiency and long lifespan.
• Signal transmission: LEDs are used in optical communication systems for transmitting signals through optical fibers.

• Positive half-cycle: During the positive half-cycle of the AC signal, two diodes conduct, allowing current to flow through the load in one direction.
• Negative half-cycle: During the negative half-cycle, the other two diodes conduct, also allowing current to flow through the load in the same direction.

Forward current:

• Direction: Flows when the diode is forward biased (positive terminal connected to the p-type material and negative terminal to the n-type material).
• Depletion region: Forward bias reduces the width of the depletion region, allowing charge carriers (electrons and holes) to cross the junction.
• Threshold voltage: Once the forward voltage exceeds the threshold (typically around 0.7V for silicon diodes), the forward current increases exponentially.
• Current magnitude: The forward current is large, as the diode conducts significant current when forward biased.

Reverse current:

• Direction: Flows when the diode is reverse biased (positive terminal connected to the n-type material and negative terminal to the p-type material).
• Depletion region: Reverse bias increases the width of the depletion region, preventing the flow of majority carriers and blocking significant current.
• Leakage current: Only a small leakage current flows due to the movement of minority carriers, but this current is typically very small under normal reverse bias conditions.
• Breakdown current: If the reverse voltage exceeds the breakdown voltage, a large reverse current flows, leading to breakdown, where the diode can conduct in reverse without damage if properly designed (e.g., Zener diodes).