Most spaceborne photodetection is measurement rather than imaging, and that is where a silicon photodiode earns its place: a small, passive part that reports incident flux inside a defined band and holds that response across the mission. Opto Diode, a division of ITW, builds three such families in Camarillo, California — AXUV for the soft x-ray and extreme-ultraviolet region, specified from 0.0124 nm to 190 nm and 100 eV to 50 keV with 100% internal quantum efficiency; SXUV, the radiation-hardened family for high-intensity EUV at 1 nm to 190 nm; and UVG for the deep ultraviolet at 190 nm to 400 nm. The line originated with International Radiation Detectors (IRD), acquired in 2011, and IRD detectors were used in solar space instrumentation on programs including SOHO, SNOE, SORCE, GOES, TIMED and EOS.
| AXUV band | 0.0124–190 nm |
| SXUV band | 1–190 nm |
| UVG band | 190–400 nm |
| Vacuum temp range | −20 to 80 °C |
| Screening | JANTX–JANS |
Those notes are introductory, and the IRD note AXUV Operating Principles and Applications (PDF) is undated and predates the current catalog, so its program-specific passages are historic. Device specifications here come from the current product pages and their controlled datasheets; where a note and a product page differ, the product page governs. Opto Diode lists three applications for the AXUV family — electron detection, synchrotron radiation monitoring and electron reticle inspection; the space work below is documented use, not a change to that listing.
Why silicon photodiodes go to orbit
Imaging drives a design toward arrays; measurement and calibration drive it toward single photodiodes selected for minimal drift — irradiance in a band, one emission line tracked across a decade, a Sun vector, or a reference channel that holds a larger instrument’s calibration. The IRD note sets AXUV photodiodes against tube-type XUV detectors and names what they offer instead.
Low mass, large area-to-size ratio
The two properties the note calls out as making these diodes attractive for satellites and deep space probes. Signal per unit of envelope.
No external operating voltage
One less high-voltage supply to qualify and shield — though the fastest catalog parts are specified under reverse bias.
Insensitive to magnetic fields
A solid-state junction has no electron optics for a field to deflect. Opto Diode publishes no magnetic-field test limit, so send the field strength with the requirement.
Low noise, eight-plus orders of dynamic range
With stability, homogeneity of quantum efficiency, small size and ruggedness, these are the grounds on which the note records approval as XUV transfer standards.
UHV compatible, operated open face
Windowless AXUV devices run open-faced down to angstrom wavelengths, even in the presence of gases — no window to solarize and none to characterize.
Radiation hardness: which figure belongs to which family
Radiation is the stressor that ends detector lifetimes on orbit. Two published figures bear on these families, and they are not interchangeable.
UVG, oxynitride window. n-on-p diodes are more radiation-hard than the more common p-on-n devices (Korde et al., IEEE Transactions on Nuclear Sciences, Vol. 36, 2169–2175, 1989), which is what makes the UVG construction better suited to space missions than conventional silicon. Diodes fabricated by incorporating nitrogen into the passivating oxide were reported at 1 G-rad (SiO2) hardness by Korde, Cable and Canfield (IEEE Transactions on Nuclear Sciences, Vol. 40, no. 6, 1655–1659, 1993) — about 10,000 times the hardness of the p-on-n photodiodes then in common use. See UVG photodiode operating principles.
SXUV, metal-silicide window. Opto Diode’s EUV 13.5 nm power and dose monitoring page states that SXUV uses a metal-silicide entrance window in place of a conventional oxide window, preserving internal quantum efficiency and holding responsivity stable after multi-G-rad accumulated dose — the exposure that degrades ordinary oxide-windowed silicon. No numeric dose limit is published on the SXUV product page or on any SXUV datasheet.
What is not published — ask for it
The AXUV entrance window is an extremely thin (3 to 7 nm) radiation-hard silicon dioxide layer. Opto Diode publishes no total-ionizing-dose rating for the AXUV family, and the two figures above belong to the UVG and SXUV constructions respectively — do not carry either across to an AXUV part in a radiation budget.
No displacement-damage, single-event or proton-fluence data is published for any of the three families, and none carries a published space qualification level as a catalog part. Send your dose, particle environment and screening requirement and ask what can be characterized for it.
Flight heritage, historically framed
The IRD note records that AXUV photodiodes were successfully used in solar space instrumentation, naming among them the European SOHO and the American SNOE, SORCE, GOES, TIMED and EOS programs. Separately, UVG photodiodes with 4 mm and 5 mm diameter active areas were used in the Multi-Angle Imaging SpectroRadiometer (MISR), launched in December 1999 as part of NASA’s Earth Observing System (Jorquera et al., Proc. IGARSS ’94). Read both as heritage rather than as current qualification: the note predates the present catalog, and Opto Diode publishes no equivalence between the devices flown then and any current part number.
Choosing the family by band
Silicon responds from the soft x-ray and ultraviolet region through the visible to a cutoff near 1.1 µm. Beyond it, InGaAs covers roughly 900 nm to 1700 nm — see how to choose a photodetector.
| Family | Specified range | Published strengths | Listed applications | Where it fits |
|---|---|---|---|---|
| AXUV | 0.0124–190 nm; 100 eV–50 keV | 100% internal quantum efficiency; windowless below 200 nm; large detection area | Electron detection, synchrotron radiation monitoring, electron reticle inspection | Soft x-ray and EUV flux channels; low-energy electron measurement |
| SXUV | 1–190 nm | High radiation hardness; low noise; broad spectral responsivity | EUV lithography, x-ray spectroscopy, synchrotron radiation monitoring | EUV channels where accumulated dose governs lifetime |
| UVG | 190–400 nm | High UV responsivity; low dark current; high quantum efficiency | Semiconductor photolithography, aerospace and environmental sensing, UV spectroscopy | DUV and near-UV radiometry; the family with published Earth-observing heritage |
Ranges are as the product-category pages state them; the SXUV page introduces the family as 1 nm to 200 nm while its individual models are labeled 1 nm–190 nm. The first two are compared in the AXUV vs SXUV selection guide; the physics is on AXUV photodiode operating principles.
Position sensing and segmented geometries
Sun sensing, beam alignment and reflected-particle measurement all want more than one element. The IRD note records that quadrant AXUV diodes with central holes and rectangular slit openings were built specifically for synchrotron beam intensity monitoring and position sensing; the current catalog carries quadrant parts in both silicon families and a center-hole part in the AXUV line.
| Model | Part number | Geometry | Active area | As specified |
|---|---|---|---|---|
| AXUVPS7 | ODD-AXU-096 | Quad detector with a hole in the center of the array, for measuring reflected electrons | 36.5 mm² per element; 146 mm² total circular active area | Responsivity 0.08 A/W typ (0.07 min, 0.09 max); Rsh 10 MΩ min; C 2 nF typ, 6 nF max; rise time 2 µs max at VR = 2 V, RL = 50 Ω |
| AXUV63HS1-CH | ODD-AXU-051 | Circular, center hole, high speed | 63 mm² | See datasheet |
| SXUVPS4 | ODD-SXU-013 | Circular active area, 4 quadrants | 1.25 mm² per element; 5 mm² total | See datasheet |
| SXUVPS4C | ODD-SXU-023 | Quadrant UV-enhanced photodiode | 1.25 mm² per element; 5 mm² total | See datasheet |
The AXUVPS7 figure that gets misquoted is the area: its datasheet specifies every electro-optical parameter per element, so 36.5 mm² is the per-element value and 146 mm² the four-element total. Size the front end on one element rather than on the whole device — the datasheet gives capacitance as 2 nF typical, 6 nF maximum, per element. One thermal caveat also matters more in orbit than on a bench — the part is rated −10 °C to 40 °C in ambient conditions but −20 °C to 80 °C in nitrogen or vacuum, and its datasheet warns that exceeding those limits may create oxide growth on the active area, compromising responsivity to low-energy radiation and to wavelengths below 150 nm over time.
Qualification, screening and traceability
Design, wafer fabrication, assembly and test all happen at the one Camarillo facility, where a dedicated high-reliability assembly area builds sensor units optimized for space, military and medical applications. The capabilities published on the custom photodiodes and detectors page are the ones a flight program cares about:
- MIL-PRF-19500 qualification — screening and qualifying semiconductor devices to JANTX through JANS classes in the dedicated Hi-Rel area, plus MIL-Standard testing or screening to a detailed customer specification.
- ISO 9001:2015 certified, and capable of meeting AS9100 standards.
- Lot traceability — every manufacturing lot traceable down to individual components such as bond wires, adhesives, silicones and epoxies.
- ITAR registered, supporting defense and export-controlled programs.
- Characterization — responsivity from 250 nm to 1100 nm with 13.5 nm calibration on request, shunt resistance and dark current, reverse breakdown voltage and response times, burn-in and lifetime exposure testing, and mechanical inspection to 0.001″ (25 µm).
Active-area size and shape, quadrant and center-hole layouts, integrated thin-film filters and complete optoelectronic assemblies are all built to specification.
Scoping a space instrument?
Send the spectral band, expected flux and required stability, the radiation and thermal environment, the vacuum interface, and your screening level. Our applications engineers will tell you which family fits and what a custom geometry or screening flow would take. Standard response to an online request is within 1–2 business days; direct orders must meet a $3,000 minimum.
Frequently Asked Questions
Which Opto Diode photodiode family suits a spaceborne UV, EUV or soft x-ray channel?
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Match the family to the band. AXUV is specified for photons, electrons or X-rays from 0.0124 nm to 190 nm and energies of 100 eV to 50 keV with 100% internal quantum efficiency, and is windowless for enhanced response below 200 nm. SXUV covers 1 nm to 190 nm and is the radiation-hardened family. UVG covers 190 nm to 400 nm. Silicon stops responding near 1.1 µm, so near-infrared channels need InGaAs at roughly 900 nm to 1700 nm instead.
How radiation-hard are these photodiodes?
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The published figures are family-specific and should not be carried across. Diodes fabricated by incorporating nitrogen into the passivating oxide, the construction used for the UVG oxynitride window, were reported at 1 G-rad silicon dioxide hardness by Korde, Cable and Canfield in IEEE Transactions on Nuclear Sciences, Vol. 40, no. 6, 1655 to 1659, 1993. Opto Diode’s EUV 13.5 nm power and dose monitoring page separately credits the SXUV metal-silicide entrance window with holding responsivity stable after multi-G-rad accumulated dose, though no numeric dose limit appears on the SXUV product page or datasheets. Opto Diode publishes no total-ionizing-dose rating for the AXUV family, and no displacement-damage or single-event data for any family.
What flight heritage do these detectors have?
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The IRD application note records that AXUV photodiodes were successfully used in solar space instrumentation, naming among them the European SOHO and the American SNOE, SORCE, GOES, TIMED and EOS programs. UVG photodiodes with 4 mm and 5 mm diameter active areas were used in the Multi-Angle Imaging SpectroRadiometer, MISR, launched in December 1999 as part of NASA’s Earth Observing System. Both records are historic, and Opto Diode publishes no equivalence between the devices flown then and any current part number.
What is the AXUVPS7 active area, and can Opto Diode screen parts for a flight program?
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The AXUVPS7, part number ODD-AXU-096, is a quad electron detector with a hole in the center of the array for measuring reflected electrons. Its active area is 36.5 mm² per element, giving a 146 mm² total circular active area, and every electro-optical parameter on its datasheet is specified per element. Opto Diode qualifies semiconductor devices to MIL-PRF-19500, JANTX through JANS classes, in a dedicated high-reliability assembly area, is ISO 9001:2015 certified and capable of meeting AS9100 standards, and is ITAR registered.
Related
Device specifications from the linked Opto Diode product-category pages and their controlled datasheets. Application context from the IRD application note AXUV Operating Principles and Applications, the Opto Diode space application notes linked above, and the cited literature. Reviewed and updated August 2026.