When leakage is really the test setup
A practical way to separate a device’s dark current from settling, cable leakage, and stray light.
Start with a baseline
A source-measure unit can report a small current even when the device is contributing very little. Cable insulation, fixtures, and stray light can all affect the reading. Check the setup background under appropriate conditions before interpreting the device trace, and keep the shielding and cable routing consistent between measurements.
Test the settling time
A voltage step can charge capacitance in the device and cables. If you record current too soon, part of what you see may be a transient. At a representative bias, compare readings at a few delays. If they drift toward a stable value as you wait, use that observation to choose the sweep delay instead of assuming every point has settled.
Change one thing at a time
Guarding can reduce leakage through the measurement path and improve settling in supported low-current setups. Follow the instrument’s connection guidance, then compare the background before and after the change. Repeat the same sweep after adjusting a delay, fixture, or shielding condition. If the apparent leakage follows the setup change, that gives you a lead to investigate before attributing the difference to the device.