Calculator inputs
Choose a method, enter device and measurement values, then generate a density estimate and energy-profile plot.
Example data table
| Method | Key inputs | Estimated density |
|---|---|---|
| Charge–Energy | Qss = 2 pC, Area = 0.01 cm², Window = 0.20 eV | 6.24e+09 cm-2 eV-1 |
| Stretch-Out | Cox = 18 nF, ΔV = 0.12 V, Area = 0.01 cm², Window = 0.30 eV | 4.49e+12 cm-2 eV-1 |
| Conductance Peak | Gp = 22 µS, f = 100 kHz, Area = 0.01 cm² | 5.47e+10 cm-2 eV-1 |
Formula used
1) Charge–Energy Method
Dss = Qss / (q × A × ΔE)
Use this when total interface charge is known over an energy interval. Here, q is the elementary charge, A is area, and ΔE is the energy window.
2) Stretch-Out Method
Dss = (Cox × ΔV) / (q × A × ΔE)
This approximation relates the measured voltage stretch in a capacitance curve to interface states distributed over the chosen energy span.
3) Conductance Peak Method
Dit = [2.5 × (Gp / ω)] / (q × A)
This method uses the peak parallel conductance response. Angular frequency is ω = 2πf. It is often used for interface trap estimation near the measured bias condition.
Additional derived values
Narea = D × ΔE
Ndevice = Narea × A
Qeq = Ndevice × q
How to use this calculator
- Select the most suitable method for your available measurement data.
- Enter the device area and choose the correct area unit.
- Set the energy start and energy end values to define the analysis window.
- Choose a graph profile and adjust peak reference energy and spread if needed.
- Complete the method-specific fields such as charge, capacitance shift, or conductance response.
- Click Calculate Density to show the result above the form.
- Review the summary metrics, graph, and derived totals.
- Use the CSV or PDF buttons to export your result set.
FAQs
What does surface state density mean?
It describes how many interface or surface states exist per unit area and per unit energy. Higher values usually indicate more trapping sites at a semiconductor boundary.
Which method should I choose?
Use charge–energy when you know total interface charge, stretch-out when you have capacitance-voltage shift data, and conductance when you measured a conductance peak versus frequency or bias.
Why is device area important?
Surface state density is normalized by area. A larger device spreads the same charge or conductance response over more surface, which lowers the calculated density.
Why do I need an energy window?
Charge-based and stretch-out estimates distribute measured effects across a selected energy range. A wider window lowers density if the same total charge is spread more broadly.
What does the conductance method estimate?
It estimates interface trap density from the parallel conductance response near a peak condition. It is often useful for MOS and semiconductor interface characterization.
Is the graph a measured spectrum?
No. The graph is a modeled profile scaled from the computed density. It helps visualize possible distribution shapes across the selected energy interval.
Can I export the calculation?
Yes. The calculator provides CSV export for numeric values and PDF export for a quick shareable result snapshot.
What units are returned?
The main result is reported in cm⁻² eV⁻¹, with an additional converted value in m⁻² eV⁻¹. Derived totals also show trap density over the window and equivalent charge.