Schottky diode reverse leakage is the cost of the low forward voltage that makes these devices attractive. The metal-semiconductor junction conducts at a much lower forward voltage than a conventional junction, and the same physics produces a reverse leakage current that is orders of magnitude larger and that rises steeply with both temperature and reverse voltage.
Why the junction behaves this way
A conventional diode uses a junction between two doped semiconductor regions, and conduction requires enough forward bias to overcome the built-in potential. A Schottky diode instead uses a junction between a metal and a semiconductor, where the barrier to conduction is lower, so forward conduction begins at a smaller voltage. The same lowered barrier means that carriers can also cross it in reverse more readily, especially as thermal energy increases. Manufacturers can adjust the barrier height by choosing different metals, trading forward drop against leakage and reverse voltage capability. That is why a low forward voltage part typically has higher leakage and a lower reverse voltage rating, while a part rated for higher reverse voltage has a larger forward drop.
Leakage rises fast with temperature
The increase is not gentle. Reverse leakage in these devices climbs steeply as the junction warms, often by a large multiple across a normal operating temperature range, and it also increases with applied reverse voltage. Because leakage current flowing under reverse voltage dissipates power, and that dissipation raises the junction temperature, which raises the leakage again, the possibility of thermal runaway exists. It is a genuine failure mode for Schottky devices operated near their reverse voltage rating at high ambient temperature, particularly in a poor thermal environment. The practical defense is to derate reverse voltage substantially, keep the junction cool, and check the datasheet’s leakage curves at the worst-case combination of voltage and temperature rather than at the room-temperature test point.
Where the trade pays and where it does not
In a low-voltage rectifier the forward drop dominates the loss, and reducing it from a diode junction’s drop to a Schottky’s can improve efficiency substantially, especially when the output voltage itself is small. In a freewheeling role during dead time, the lower drop reduces conduction loss and the absence of significant stored charge avoids the recovery losses of a conventional junction. Against that, a circuit that spends most of its time reverse biased at high voltage and high temperature may lose more to leakage than it saves in conduction. Battery-powered circuits where quiescent drain matters are particularly sensitive, since leakage is a continuous drain that appears as shortened standby life rather than as heat.
Recovery behavior is the other half of the appeal
Schottky conduction is by majority carriers, so there is very little stored charge to remove when the device is reverse biased. That means effectively no reverse recovery current in the way a conventional rectifier exhibits, which reduces switching loss in the diode and in the transistor commutating it, and reduces the ringing and emissions that recovery current produces. There is still junction capacitance to charge, which produces a current spike, but it behaves quite differently from stored charge recovery. This property is why Schottky devices are standard in high-frequency switching converters and why placing one in parallel with a MOSFET’s body diode is a recognized technique for improving bridge behavior. That benefit only materializes when the parallel path is physically short, because any inductance between the two devices lets the slower junction conduct first and the advantage disappears into the layout.
Selecting and verifying a device
Read the reverse leakage specification at the highest junction temperature and the highest reverse voltage your circuit applies, and compute the resulting dissipation. Add that to the conduction loss and check the total against the thermal path you have. Confirm the reverse voltage rating with real margin, remembering that switching circuits produce ringing well above the nominal rail. For standby-sensitive designs, calculate the leakage current as a continuous drain over the standby period. On the bench, measure the device temperature under the worst-case reverse bias condition at maximum ambient, because leakage-driven heating appears only in that condition and will not show up in a normal functional test at room temperature.
What to check before you act
- Read leakage at maximum junction temperature and maximum reverse voltage.
- Add leakage dissipation to conduction loss in the thermal budget.
- Derate reverse voltage generously, allowing for switching ringing.
- Count leakage as a continuous drain in any standby power calculation.
Common questions
Is a Schottky always more efficient than a standard rectifier?
Not always. At low output voltage and high current it usually is, but in a high-voltage, high-temperature, mostly reverse-biased role the leakage can outweigh the saving.
Why does my circuit draw more standby current when warm?
Reverse leakage in Schottky devices rises steeply with temperature, so a diode that leaks negligibly on the bench can leak measurably inside a warm enclosure.
The practical takeaway
Choose a Schottky for its low forward drop and its lack of stored charge, then check what its leakage costs at your highest junction temperature and reverse voltage. Derate the reverse voltage with margin for ringing, include leakage in both the thermal and the standby budgets, and verify the hot case on hardware.
References and further reading
- Department of Energy: how electronics losses turn into wasted energy and heat
- ENERGY STAR: standby power losses in everyday electronic equipment
- CPSC: safety guidance for electronics and electrical products indoors
Numerical scenarios are illustrative unless identified otherwise. Follow the exact product instructions; component ratings and local installation requirements can differ.
