What is the photon detection efficiency (PDE) of a SiPM?
Photon detection efficiency (PDE) refers to the probability that a photon arriving on the SiPM surface is detected, an initiates the process of current pulse generation. PDE is a function of the overvoltage ΔV across the terminals of the APD and wavelength λ of the incident photon. Photon detection efficiency is one of the most important characteristics of a SiPM.
PDE is the product of three factors :- Geometrical fill factor (FF), Quantum Efficiency (QE) and Probability of a Geiger discharge. (Pt)
PDE (Vov) = Qe x Pt (Vov) x FF
Geometrical fill factor(FF)
A SiPM is a pixelated device and all the pixels(microcells) are of the same size and arranged in a tiled pattern. The total area on which the pixels of the SiPM lie is its active area. But in each microcell, only a fraction of its area is photosensitive. This fraction of the photosensitive area, equated to the active area is refferd to as the Geometrical fill factor which ranges from ∼30% to ∼80%. The larger the size of the microcell, the higher the geometrical fill factor.
Quantum efficiency (Qe) The quantum efficiency is the probability that incident photon will produce a charge carrier that will initiate a Geiger discharge. …show more content…
In the depletion region, a strong electric field exists which separates the photo-generated electron –hole pair, and is responsible for directing the charge carriers into the avalanche region. In the regions outside the depletion region, the electric field is very weak, hence photo-generated electron-hole pairs are more likely to recombine. Using Beers-Lambert law, the SiPM can be optimized to absorb light for a certain desired wavelength(or range of wavelengths) in the depletion layer. Hence depending on the range of the wavelengths set, the incident photon will initiate a Geiger discharge if it only falls within the limits. This is the principle used in fabrication of Near Ultaviolet(NUV) or Visible light (RGB) SiPMs. Probability of Geiger discharge Once the charge carrier generated by the incident photon is injected into the avalanche region, it gains Kinetic energy from the electric field set up in this region. This energy must reach a certain threshold so that the charge carrier may be able to impact-ionize the silicon atoms to initiate an avalanche. The likelihood of an avalanche being initiated depends on these three factors: 1) The strength of the electric field set up in the depletion region, which is controlled by the overvoltage ΔV. 2)The width of the avalanche region,since the wider the region, the higher the likelihood of impact-ionization. The width of the avalanche region is also determined by the overvoltage ΔV 3) collisional cross section of charge carriers with phonons and the specific history of these interactions. When the overvoltage, ΔV < 0, the probability of Geiger discharge are extremely low. With increase in overvoltage ΔV, the strength of the electric field and width of the avalanche region increases hence greatly improving the probability of a Geiger discharge occurring. Breakdown Voltage The breakdown voltage (Vbd) in an APD is the minimum (reverse) bias voltage that results in self-sustaining avalanche multiplication. Only when VBIA is above VBD will an output current pulse be observed. The difference between VBIA and VBD is the overvoltage ΔV which as we have seen is the parameter that controls the operation of the SiPM. Increase in overvoltage ΔV increases the performance of the SiPM by improving the Photon Detection efficiency but there is an optimum upper limit for the VBIA to ensure that noise disturbances do not interfere with the operation of the SiPM as noise also increases with increase in the overvoltage. The breakdown voltage is temperature dependant, hence in the datasheets, it is specified the breakdown voltage at a certain temperature. The breakdown voltage temperature dependence depends on the internal characteristics of the Avalanche Photo Diode(APN). The recovery time of SiPM is the time it takes between the quenching of the avalanche and when the microcell fully resets and gains the ability to detect an incoming photon. During the recovery time, the microcell slightly looses its ability to detect new incoming photons. The time constant of the recovery phase is RQCJ (Product of the quenching resistance and junction resistance) Temperature has several effects on the operation of SiPM as it directly influences some of
Photon detection efficiency (PDE) refers to the probability that a photon arriving on the SiPM surface is detected, an initiates the process of current pulse generation. PDE is a function of the overvoltage ΔV across the terminals of the APD and wavelength λ of the incident photon. Photon detection efficiency is one of the most important characteristics of a SiPM.
PDE is the product of three factors :- Geometrical fill factor (FF), Quantum Efficiency (QE) and Probability of a Geiger discharge. (Pt)
PDE (Vov) = Qe x Pt (Vov) x FF
Geometrical fill factor(FF)
A SiPM is a pixelated device and all the pixels(microcells) are of the same size and arranged in a tiled pattern. The total area on which the pixels of the SiPM lie is its active area. But in each microcell, only a fraction of its area is photosensitive. This fraction of the photosensitive area, equated to the active area is refferd to as the Geometrical fill factor which ranges from ∼30% to ∼80%. The larger the size of the microcell, the higher the geometrical fill factor.
Quantum efficiency (Qe) The quantum efficiency is the probability that incident photon will produce a charge carrier that will initiate a Geiger discharge. …show more content…
In the depletion region, a strong electric field exists which separates the photo-generated electron –hole pair, and is responsible for directing the charge carriers into the avalanche region. In the regions outside the depletion region, the electric field is very weak, hence photo-generated electron-hole pairs are more likely to recombine. Using Beers-Lambert law, the SiPM can be optimized to absorb light for a certain desired wavelength(or range of wavelengths) in the depletion layer. Hence depending on the range of the wavelengths set, the incident photon will initiate a Geiger discharge if it only falls within the limits. This is the principle used in fabrication of Near Ultaviolet(NUV) or Visible light (RGB) SiPMs. Probability of Geiger discharge Once the charge carrier generated by the incident photon is injected into the avalanche region, it gains Kinetic energy from the electric field set up in this region. This energy must reach a certain threshold so that the charge carrier may be able to impact-ionize the silicon atoms to initiate an avalanche. The likelihood of an avalanche being initiated depends on these three factors: 1) The strength of the electric field set up in the depletion region, which is controlled by the overvoltage ΔV. 2)The width of the avalanche region,since the wider the region, the higher the likelihood of impact-ionization. The width of the avalanche region is also determined by the overvoltage ΔV 3) collisional cross section of charge carriers with phonons and the specific history of these interactions. When the overvoltage, ΔV < 0, the probability of Geiger discharge are extremely low. With increase in overvoltage ΔV, the strength of the electric field and width of the avalanche region increases hence greatly improving the probability of a Geiger discharge occurring. Breakdown Voltage The breakdown voltage (Vbd) in an APD is the minimum (reverse) bias voltage that results in self-sustaining avalanche multiplication. Only when VBIA is above VBD will an output current pulse be observed. The difference between VBIA and VBD is the overvoltage ΔV which as we have seen is the parameter that controls the operation of the SiPM. Increase in overvoltage ΔV increases the performance of the SiPM by improving the Photon Detection efficiency but there is an optimum upper limit for the VBIA to ensure that noise disturbances do not interfere with the operation of the SiPM as noise also increases with increase in the overvoltage. The breakdown voltage is temperature dependant, hence in the datasheets, it is specified the breakdown voltage at a certain temperature. The breakdown voltage temperature dependence depends on the internal characteristics of the Avalanche Photo Diode(APN). The recovery time of SiPM is the time it takes between the quenching of the avalanche and when the microcell fully resets and gains the ability to detect an incoming photon. During the recovery time, the microcell slightly looses its ability to detect new incoming photons. The time constant of the recovery phase is RQCJ (Product of the quenching resistance and junction resistance) Temperature has several effects on the operation of SiPM as it directly influences some of