Silicon avalanche photodiodes are used in the wavelength range between 250 nm and 1100 nm. The avalanche effect of these photodiodes makes them well suited for the detection of extremely weak light intensities.
Silicon APDs for Photon Counting
The SAP-series silicon avalanche photodiodes are primarily used in photon counting. This series features highest efficiency and lowest dark current rates.
The SAP500 series is based on a "reach through” structure with excellent quantum efficiency as well as extremely low noise and dark current. This APD, which has an active area of D=500 µm, can either be operated in normal linear mode (VR < VBR) with an internal gain of 250 or more or in "Geiger” mode.
In "Geiger” mode the APD is operated at a voltage that is larger than the breakdown voltage (VR > VBR); in this mode, single photons can be detected.
The new SAP500 series is well suited for applications that quantify the weakest light signals (including single photons) and detect them in a time-resolved manner (e.g., LIDAR, spectroscopy, fluorescence measurements, or photon counting). The advantages compared to photomultipliers (PMTs) are as follows:
- Small compact design
- Very high quantum efficiency
- Not sensitive to magnetic fields
- Long lifetime
- Very good time resolution
- Smaller operating voltage
The SAP-500 series is available in a modified, hermetically-sealed TO-46 housing. A version is also available with a single-stage thermoelectric cooler in a TO-37 housing or a double-stage TEC in a TO-8 housing.