CSE Assignment-1 Unit 1

Energy Band Diagram

• Conductors: Have overlapping energy bands, allowing easy flow of electrons. No energy gap; excellent electrical conductors (e.g., metals).
• Insulators: Possess a large energy gap between the valence band and conduction band, preventing electron flow. Poor conductors of electricity (e.g., rubber, glass).
• Semiconductors: Have a smaller energy gap, allowing some electron transition from the valence band to the conduction band. Conductivity can be manipulated by temperature or doping.

N-type vs P-type Semiconductors

• N-type: Doped with electron-rich elements (e.g., phosphorus) adding extra electrons to the conduction band, which increases conductivity.
• P-type: Doped with electron-deficient elements (e.g., boron) creating "holes" or vacancies in the valence band, effectively allowing positive charge carriers.

Forward Bias and Reverse Bias

• Forward Bias: A condition where the positive terminal of a power source connects to the P-side and the negative terminal to the N-side of a diode, allowing current to flow.
• Reverse Bias: A condition where the positive terminal connects to the N-side and the negative terminal to the P-side, preventing current flow, except for negligible leakage current.

V-I Characteristics of PN Junction Diode

• Current-Voltage (V-I) characteristics showcase a diode's behavior under forward and reverse bias.
• In forward bias, the diode conducts current after reaching a threshold voltage (typically 0.7V for silicon).
• In reverse bias, the current remains minimal until breakdown voltage is reached, at which point the diode may conduct in reverse.

Properties of LASER

• Coherence: Emitted light is monochromatic and in phase.
• Monochromaticity: Produces light of a single wavelength.
• Directionality: Laser light is emitted in a narrow beam with minimal divergence.
• High Intensity: Capable of focusing energy in a small area.

He-Ne Laser

• A common type of gas laser, uses a helium-neon gas mixture.
• Has an energy diagram displaying the excitation of helium atoms, transferring energy to neon atoms to produce laser light.
• Typical wavelength is 632.8 nm (red light).

Applications of LASER

• Used in telecommunications for high-speed data transfer.
• Employed in medical fields for procedures like eye surgery.
• Essential in industrial applications such as cutting, welding, and engraving materials.
• Utilized in barcode scanners and optical storage devices (CD/DVD).