Semiconductors-pn junction diodes.BJTpptx

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1. Semiconductors, PN Junctions, and Diodes A semiconductor is  a material whose ability to conduct electricity is between that of a conductor (like copper) and an insulator (like glass) . Presented by: Ibrar Younis Semiconductors weren't "discovered" by a single person, but rather through a series of discoveries by multiple scientists, including  Michael Faraday , who first observed a semiconductor effect in 1833. 

2. Types of Semiconductors Intrinsic semiconductors, which are pure materials like silicon or germanium, and extrinsic semiconductors, which are doped with impurities to enhance conductivity. Stable Particle: Electrons maintain their properties over time. Negative Charge: Key for electrical interactions. Fundamental Role: Crucial for atomic structure and electrical conductivity.

3. Band Gap Energy The concept of the band gap in semiconductors originated from the 927 energy band theory by Walter Heitler . The band gap energy of semiconductors is  the energy difference between the top of the valence band and the bottom of the conduction band. The minimum amount of energy required to excite an electron from valance to conduction band. Example of Semiconductors Types N-Type Pentavalent Impurities ( Phosphorus (P) , atomic number is 13, majority of electrons P-Type trivalent impurities (Aluminum ) , atomic number is 13

4. The PN Junction A PN junction is formed when P-type and N-type semiconductor materials are joined together. At this interface, free electrons from the N-side diffuse into the P-side, and holes from the P-side diffuse into the N-side. Shockley discovered the PN junction diode in 1949

5. Depletion Region A depletion region is an insulating area within a semiconductor device where free mobile charge carriers (electrons and holes) are absent or have diffused away, creating a net immobile charge and an internal electric field .

6. PN Junction Biasing Forward Bias A positive voltage is applied to the P-side and a negative voltage to the N-side. This reduces the potential barrier, allowing majority carriers to flow across the junction, resulting in significant current flow. A negative voltage is applied to the P-side and a positive voltage to the N-side. This increases the potential barrier and widens the depletion region, preventing majority carriers from flowing and resulting in negligible current (only a small leakage current). This unidirectional current flow characteristic is what makes the PN junction ideal for diode applications. Reverse Bias

7. Diode A diode is a two-terminal electronic component that functions like a one-way valve for electrical current, allowing it to flow in one direction (forward bias) while restricting it in the opposite direction (reverse bias). Working Principle: It is based on the PN junction . When forward-biased (positive terminal to P-type, negative to N-type), the potential barrier reduces, allowing current to flow. When reverse-biased, the depletion region expands, blocking current flow (except a tiny leakage current).

8. Diode Types Light Emitting Diode (LED): Emits light when forward biased. Laser Diode: Produces coherent light, used in optical drives and fibre optics. Avalanche Diode: Designed for controlled breakdown in reverse bias, used in high-voltage protection. Zener Diode: Maintains a constant voltage under reverse breakdown, ideal for voltage regulation. Schottky Diode: Features a metal-semiconductor junction, offering faster switching and lower forward voltage drop. Photodiode: Converts light into electrical current, used in light detection.

9. Diode Characteristics & Uses Key Characteristics Forward Bias Low resistance, allowing current flow above threshold voltage. Reverse Bias High resistance, blocking current flow (except for minor leakage). Zero Bias No external voltage, only diffusion current until equilibrium. Versatile Applications Rectifiers Converting AC to DC power in power supplies. Clipping & Clamping Shaping waveforms and shifting DC levels in signal processing. Logic Gates Forming basic digital logic circuits (AND,OR gates).