Semiconductor materials play a crucial role in the functioning of electronic devices, bridging the gap between conductors and insulators. Their unique properties stem from their atomic structure and the ability to alter conductivity through doping.
| 🔬 Concept | ⚡ Key Point | 🌍 Application |
|---|---|---|
| Semiconductor Materials | Have conductivity between conductors and insulators | Used in electronic devices like transistors and diodes |
| Doping | Introduction of impurities to modify conductivity | Creates n-type and p-type semiconductors |
| Current Density | Flow of electric charge per unit area | Essential for understanding semiconductor behavior |
🧪 Core Principles
Semiconductor Materials
- Defined as materials with conductivity levels between conductors and insulators.
- Conductors (e.g., copper) have low resistivity (~10^-6 ohm-cm).
- Insulators (e.g., mica) exhibit high resistivity (~10^12 ohm-cm).
- Semiconductors like germanium and silicon have resistivity values (~50 ohm-cm for germanium and 50 x 10^3 ohm-cm for silicon).
Energy Band Diagrams
- Insulators have a large energy gap (~6 eV) making them non-conductive.
- Semiconductors have a smaller energy gap (~1 eV), allowing conductivity.
- Conductors have overlapping bands with zero energy gap facilitating easy charge flow.
⚗️ Process
Intrinsic vs. Extrinsic Semiconductors
- Intrinsic Semiconductors: Pure form where conductivity increases with temperature due to more free electrons.
- Extrinsic Semiconductors: Formed by doping with impurities.
- n-type: Doping with pentavalent impurities adds excess electrons.
- p-type: Doping with trivalent impurities creates holes (deficiency of electrons).
Charge Carriers
- n-type semiconductors have electrons as majority carriers and holes as minority carriers.
- p-type semiconductors have holes as majority carriers and electrons as minority carriers.
🌍 Applications
Current Flow in Semiconductors
- Current in semiconductors flows due to electron movement, with conventional current moving in the opposite direction of electron flow.
- The mass action law states that under thermal equilibrium, the product of free electron and hole concentrations is constant: np = n_i².
- Charge densities are affected by doping levels, leading to the equations:
- For n-type: N_D + p = n
- For p-type: p = N_A + n
Current Density Calculation
- Current density (J) can be calculated using: