UV Photodiode
Generates a photocurrent proportional to UV irradiance in a defined sub-band (200–280 nm UV-C, 280–315 nm UV-B, or 315–400 nm UV-A), output through a transimpedance amplifier as a calibrated UV index or W/m² value.
A wide-bandgap semiconductor PN junction (SiC's 3.26 eV or GaN's 3.4 eV) absorbs photons whose energy exceeds the bandgap, generating electron-hole pairs that the bias field separates into photocurrent. Bandgap-tuning makes the sensor blind to wavelengths longer than its cutoff (e.g., a 280 nm SiC sensor is solar-blind). On-chip optical filters narrow the response to a specific UV sub-band; a TIA converts photocurrent to voltage.
In plain terms
Like a smoke detector that sees only the colour of fire — invisible to room lights and sunlight, but lights up the moment a UV-emitting flame appears.
Why designers use it
- Flame detection — hydrocarbon flames emit strongly in UV-C; a solar-blind sensor sees the flame even with sunlight streaming in.
- UV index — wearables and weather stations use UV-A/B sensors to warn users of sunburn risk.
- UV-curing process control — semiconductor lithography and printing measure the UV dose applied to a substrate.
- Solid-state replacement for fragile vacuum UV tubes — no high-voltage supply, no cathode-poisoning, much longer life.
Best for
- Flame detect
- UV index
- Lithography monitors
Key specifications
- Operating limits: Check the exact manufacturer's datasheet (A family name does not establish voltage, current, temperature or timing limits.)
- Pin assignment: Match the complete part and package code (A similar name or function does not guarantee the same wiring.)
- Mechanical fit: Use the exact package drawing (Check pad layout, dimensions and viewing direction before building.)
When not to use it
- Where visible-light response is acceptable — a standard silicon photodiode with a UV-pass filter is much cheaper.
- For high-power UV-C measurement (germicidal lamps near saturation) — wide-bandgap diodes saturate; pull thermal pyroelectric.
Common mistakes
- Forgetting the chip's spectral response curve — a 300 nm sensor reads zero on a 400 nm UV-A LED but the user assumes it's broken.
- Routing the high-impedance photodiode trace next to a switching power rail — pickup couples in and the TIA outputs phantom UV.
Where you will find it
- A Det-Tronics X3301 multispectrum flame detector on a Shell offshore platform uses a SiC UV-C photodiode alongside IR sensors: the SiC element rejects the noonday sun and the chemiluminescent flicker of welding arcs, firing the deluge only on actual hydrocarbon fires within 15 m.
- A Vishay VEML6075 UVA/UVB sensor in a Garmin Fenix 7 sport watch reports daily UV exposure: the chip's calibrated UV-index output drives sunburn-risk warnings, and its solar-blind silicon design works through transparent bezels without false readings indoors.
- A Hamamatsu C12880MA mini-spectrometer's deep-UV (200 nm) channel uses a GaN photodiode behind a quartz window: the chip lets a portable air-quality lab measure tropospheric ozone via the Hartley absorption band without the cost of a full UV monochromator.
A short history
UV photodiodes detect radiation in the 200–400 nm ultraviolet band, below the range of conventional silicon photodiodes, which are blind to wavelengths below ~350 nm without special coatings. Hamamatsu Photonics, founded in Japan in 1953, became a leading developer of UV-sensitive photodetectors using silicon with UV-enhancing surface treatments, and later gallium nitride and silicon carbide (SiC) junctions that have bandgaps suited to UV detection with suppressed visible-light response ("solar-blind" behaviour). UV photodiodes are essential in flame detectors for gas turbines and boilers (UV emission of a hydrocarbon flame), UV-index sensors for consumer wearables, ozone monitoring, and UV-curing process control in printing and semiconductor lithography. The development of GaN-based UV photodiodes in the 1990s enabled compact, solid-state flame sensors that replaced vacuum-tube UV tubes.