Photodiodes for Accurate Light Detection

Did You Know?

Did you know that the junction capacitance of a silicon photodiode (often 2–50 pF depending on area and reverse bias) fundamentally limits its bandwidth, with f−3 dB ≈ 1∕(2πRC), where R is the load or transimpedance input resistance? A common misconception is that operating a photodiode in photovoltaic (zero-bias) mode is always better for low noise—in reality, a modest reverse bias typically reduces capacitance, increases speed, and can improve signal-to-noise in high-speed or low-signal applications despite the added dark current. Another subtle effect is that quantum efficiency and responsivity are wavelength-dependent (e.g., Si peaks near ~0.5–0.6 A/W around 850 nm), so specifying only "A/W" without a wavelength is incomplete and often misleading.
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Frequently Asked Questions

A photodiode is a semiconductor junction device that converts incident photons into an electrical current via the internal photoelectric effect. When light with energy above the bandgap strikes the depletion region, electron-hole pairs are generated and separated by the built-in electric field, producing a photocurrent proportional to incident optical power within the device’s linear range.

Photodiodes for Optical Sensing and Measurement

Photodiodes are semiconductor-based light detectors that convert incident photons into electrical current. On FindLight, photodiodes span silicon, InGaAs, germanium, and other materials to cover spectral ranges from the UV through visible and into the near- and short-wave infrared. Devices are available as bare chips, packaged components, and integrated detector modules.

Key Specifications of Photodiodes

When selecting photodiodes, engineers typically evaluate spectral response, active area, responsivity, speed, and noise performance. Common wavelength coverage includes 190–1100 nm for silicon photodiodes and up to ~2.6 µm for InGaAs and Ge devices. Active areas range from sub-mm² for high-speed detection to tens of mm² for high-collection efficiency.

Other important parameters include dark current, shunt resistance, junction capacitance, and noise-equivalent power (NEP). For high-speed applications, low capacitance and short rise times are critical, with some photodiodes supporting bandwidths in the GHz regime. Many products support operation in photovoltaic or reverse-biased photoconductive modes, with packaging options such as TO-cans, SMD packages, and fiber-coupled housings.

Typical Applications of Photodiodes

Photodiodes on FindLight are used in optical power monitoring, laser feedback control, spectroscopy, biomedical instrumentation, LIDAR receivers, position sensing, and general-purpose light detection. They are also integrated into OEM modules for machine vision, communication receivers, and environmental sensing.

Buyer Guidance on FindLight

To select suitable photodiodes, start by matching the spectral response to your source or signal wavelength, then compare responsivity, dark current, and active area versus your required signal level and spatial constraints. For pulsed or high-speed systems, prioritize bandwidth, rise time, and capacitance. For low-light applications, review NEP and dark current to estimate signal-to-noise performance.

On FindLight you can compare photodiodes from multiple vendors by reviewing datasheet-level specifications side by side. Filter by wavelength range, package type, and active area, then request quotes directly from suppliers. No registration is required to send inquiries, enabling rapid sourcing and technical clarification for your photodiode requirements.