Semiconductor devices:

Semiconductor devices are electronic components utilizing the properties of semiconductor materials. These materials are neither good conductors nor good insulators; examples include silicon and germanium. Their conductivity can be significantly altered by adding trace amounts of other elements, a process called doping. Diodes, transistors, photocells, and thyristors are common examples used in electronic circuits.

Advantages of Semiconductor Devices Over Thermionic Devices:

• Smaller size
• Lower cost
• Increased durability (resistance to physical shock and heat stress)
• Reduced heat generation
• Faster response times
• Ability to handle, process, and deliver multiple inputs/data streams

• A Zener diode is a p-n junction semiconductor designed to operate in its reverse breakdown region. When a reverse voltage (anode to negative, cathode to positive) is applied and reaches the Zener voltage, the diode undergoes breakdown, allowing a large current to flow while maintaining a relatively constant voltage across it.
• Applications: Voltage regulation, voltage comparison in automatic voltage regulators (AVRs).

• A transistor is a three-layered semiconductor device (npn or pnp) that amplifies and switches electronic signals and power. Its operation is based on the principle that applying a voltage causes negative charge carriers (electrons) to move in one direction and positive charge carriers (holes) in the other. The current flow in one part of the transistor is controlled by a smaller current in another part.
• Applications: Signal amplification, analog and digital switching, microprocessors.

• A photocell is a solid-state device that converts light into electrical energy. It operates on the photoelectric effect—the emission of electrons from a material's surface when light energy is applied. The incident light causes the release of electrons, generating a voltage or altering current flow.
• Applications: Alarm circuits, sound reproduction in movies, robotics.

• A thyristor is a solid-state switch turned on by a low-level signal voltage applied to a trigger connection called the gate. It's a four-layered, three-junction device that functions unidirectionally, similar to a diode. Conduction occurs only when triggered by the gate.
• Applications: Silicon-controlled rectifiers (SCRs) are used in AVRs and for controlling power to loads. They are used in high-power applications such as motor control.