Displacement Damage in Semiconductor Devices
Beyond single events, neutrons knock atoms loose in semiconductors, degrading carrier lifetime and device performance over a mission.
Damage that adds up
Neutrons displace atoms in a semiconductor crystal just as they do in structural metals. In devices, the resulting defects act as recombination centers: they shorten minority-carrier lifetime, reduce gain in bipolar parts, increase dark current in imagers, and degrade the performance of optocouplers and solar cells. This is displacement-damage dose, distinct from ionizing effects.
Which parts are sensitive
- Bipolar transistors: current gain falls
- Image sensors and detectors: dark current rises
- Optocouplers and LEDs: output degrades
- Solar cells: output power declines
Why fusion neutrons are relevant
Displacement damage scales with recoil energy, and 14 MeV neutrons produce energetic recoils that represent a demanding case. Characterizing a device against a fusion spectrum bounds its behavior for high-energy environments and supports mission-lifetime predictions.
Kronos includes device displacement testing within its neutron-service scope, reported alongside SEE cross-sections so a program sees both failure modes.
Optoelectronics are the canaries
Devices that rely on minority-carrier lifetime, bipolar transistors, photodiodes, image sensors, optocouplers, and LEDs, show displacement damage earliest, often before digital logic degrades. In a mixed-technology system they act as early indicators of accumulated dose. Characterizing these sensitive parts against a 14 MeV spectrum bounds when a subsystem's analog or optical performance will start to drift, which frequently sets the true mission lifetime rather than the digital core. Reporting displacement effects alongside single-event cross-sections gives a program the two curves it needs, gradual degradation and discrete upset, to plan a mission that stays within both budgets across its full duration.
This page describes a design and simulation study, not a built machine. The breeder (Hyperion) begins construction Q2 2027; first-of-a-kind first tritium is targeted near 2030. No hardware net-gain is claimed before then.