What Is the Hall Effect?
The Hall effect occurs when a current-carrying conductor is placed in a magnetic field perpendicular to the current. The magnetic force deflects charge carriers to one side, creating a voltage difference (Hall voltage) across the conductor. Discovered by Edwin Hall in 1879, this effect is fundamental to semiconductor characterization and magnetic field sensing.
The Hall coefficient relates the Hall voltage to the current and magnetic field. Its sign indicates the type of charge carrier: positive for holes (p-type) and negative for electrons (n-type). Its magnitude gives the carrier density, making it an essential diagnostic tool in semiconductor physics.
Hall Coefficient Formula
Hall Coefficients of Materials
| Material | RH (m³/C) | Carrier |
|---|---|---|
| Copper | -5.5 × 10⁻¹¹ | Electrons |
| Silicon (n-type) | -3.7 × 10⁻⁴ | Electrons |
| Germanium (p-type) | +9.3 × 10⁻³ | Holes |
Frequently Asked Questions
What are Hall effect sensors used for?
Hall sensors are used in automotive systems (wheel speed, position sensing), smartphones (compass, flip-cover detection), current sensors, brushless DC motor commutation, and keyboard switches. They provide contactless, wear-free sensing of magnetic fields and position.
Why is the Hall coefficient of metals so small?
Metals have extremely high carrier densities (approximately 10²⁸ to 10²⁹ per m³), resulting in very small Hall coefficients and tiny Hall voltages. Semiconductors have much lower carrier densities, making their Hall effects much more pronounced and easier to measure.