Surface Recombination Velocity Calculator

Calculator Inputs

Choose a method, enter known quantities, and calculate velocity in centimeters per second. The form adapts to flux, current, or lifetime estimation workflows.

Calculation method

Pick the relation that matches your measured semiconductor data.

Excess carrier concentration Δn_s (cm^-3)

Carrier concentration near the recombining surface.

Surface recombination flux U_s (cm^-2 s^-1)

Use measured net recombination flux at the interface.

Surface current density J_s (A/cm²)

Suitable when surface loss is inferred from measured current.

Carrier charge q (C)

Default is the elementary charge.

Effective lifetime τ_eff (μs)

Measured effective minority carrier lifetime.

Bulk lifetime τ_bulk (μs, optional)

Leave blank only if you use the simplified approximation.

Wafer or characteristic thickness W (cm)

Required for lifetime estimation and useful for derived metrics.

Interface area (cm², optional)

Used to estimate total recombination rate or total surface current.

Minority carrier diffusion coefficient D (cm²/s, optional)

Provides a derived recombination length D/S.

Example Data Table

Scenario	Method	Known Inputs	Calculated S (cm/s)	Interpretation
Passivated silicon interface	Flux	U_s = 5.0×10¹⁴, Δn_s = 1.0×10¹²	500	Moderate recombination
Current based device test	Current density	J_s = 8.0×10^-5, q = 1.602×10^-19, Δn_s = 1.0×10¹²	499.32	Moderate recombination
Thin wafer approximation	Lifetime	W = 0.02, τ_eff = 25 μs	400	Moderate recombination
Lifetime with bulk correction	Lifetime	W = 0.02, τ_eff = 25 μs, τ_bulk = 100 μs	300	Moderate recombination

Formula Used

Surface recombination velocity links interface recombination strength to carrier concentration near a surface. It is usually expressed in cm/s.

Flux method: S = U_s / Δn_s
Current density method: S = J_s / (q · Δn_s)
Lifetime method with bulk correction: S = (W / 2) · (1 / τ_eff − 1 / τ_bulk)
Simplified lifetime approximation: S ≈ W / (2 · τ_eff)
Derived surface lifetime: τ_s ≈ W / (2S)
Derived recombination length: L_s = D / S

Use the corrected lifetime form whenever bulk lifetime is known. The simplified approximation is best treated as a quick estimate.

How to Use This Calculator

Select the method that matches your measured data source.
Enter the required inputs using centimeter based semiconductor units.
Add optional area, thickness, or diffusion coefficient for extended outputs.
Press Calculate to display the result beneath the header.
Review the interpretation label and derived engineering quantities.
Use the CSV or PDF buttons to export the current result.

FAQs

1. What does surface recombination velocity represent?

It measures how quickly carriers recombine at a semiconductor surface. Larger values generally indicate poorer passivation, stronger interface defects, or higher boundary related carrier loss.

2. Which unit should I use for the final answer?

The main result is reported in cm/s, which is the standard engineering unit in semiconductor work. The calculator also shows an m/s conversion.

3. When should I use the flux method?

Use the flux method when you know the surface recombination flux and the excess carrier concentration at the interface. It is direct and physically transparent.

4. When is the current density method better?

Choose it when measurements are available as surface current density, such as from device characterization. The formula converts electrical loss into an equivalent recombination velocity.

5. Why does the lifetime method need thickness?

Thickness connects carrier lifetime to boundary loss through a diffusion style approximation. Without a characteristic thickness, lifetime alone cannot produce a velocity.

6. Why did the corrected lifetime method return an error?

If effective lifetime is not smaller than bulk lifetime, the correction term becomes zero or negative. That would imply the chosen values do not support a positive surface recombination result.

7. What is the recombination length output?

It is D/S, where D is the minority carrier diffusion coefficient. It offers a quick sense of how strongly the surface competes with diffusion driven transport.

8. Can I use this calculator for any semiconductor material?

Yes, provided your inputs use consistent units and your chosen relation is appropriate for the device physics. Interpret results within the assumptions of your measurement method.