1. What is the Diffusion Coefficient?

The diffusion coefficient (D) describes how quickly particles diffuse through a material. In semiconductors, it relates the mobility of charge carriers to thermal energy and charge through the Einstein relation.

2. How Does the Calculator Work?

The calculator uses the diffusion coefficient formula:

Where:

• \( D \) — Diffusion coefficient (cm²/s)
• \( \mu \) — Mobility of charge carriers (cm²/V s)
• \( kT \) — Thermal energy (eV)
• \( q \) — Charge of carriers (elementary charge)

Explanation: This equation shows the direct proportionality between diffusion and mobility, with thermal energy promoting diffusion and charge acting as a scaling factor.

3. Importance of Diffusion Coefficient

Details: The diffusion coefficient is crucial for understanding carrier transport in semiconductors, designing electronic devices, and modeling processes like dopant diffusion during fabrication.

4. Using the Calculator

Tips: Enter mobility in cm²/V s, thermal energy in eV, and charge in elementary charge units (typically 1 for electrons/holes). All values must be positive.

5. Frequently Asked Questions (FAQ)

Q1: What is typical mobility value for silicon?
A: For electrons in Si: ~1400 cm²/V s, for holes: ~450 cm²/V s at room temperature.

Q2: What is kT at room temperature (300K)?
A: Approximately 0.02585 eV (where k is Boltzmann's constant).

Q3: Why is charge typically 1 in this calculation?
A: For electrons and holes, the relevant charge is usually one elementary charge (1.6×10⁻¹⁹ C).

Q4: How does temperature affect diffusion coefficient?
A: Higher temperature increases both kT and typically mobility (μ), leading to greater diffusion.

Q5: What are typical diffusion coefficient values in semiconductors?
A: For electrons in Si at 300K: ~35 cm²/s, with wide variation based on material and conditions.