Quantum Efficiency

The Quantum Efficiency (QE) of the array at 600 nm is mapped in Fig. 5. The QE has been measured for each element by setting an overvoltage of 20% above the breakdown, and a hold-off time of 6 ^s. The mean value is about 57% and it is evident, at this wavelength, that there is uniform sensitivity over the array. QE curves of anode 5, cathode 4 elements obtained by biasing with three different overvoltage levels are shown in Fig. 6. As expected, QE increases with the applied bias, and this increase is due to the electric field generated on the SPAD sensitive area.

Quantum Efficiency nap 600 nm OverVoUtqe 20 % above breakdown

Quantum Efficiency nap 600 nm OverVoUtqe 20 % above breakdown

cathode 5 1 Anode

Figure 5. QE map of all the array at 600 nm, obtained by setting the hold-off time to 6 p.s.

cathode 5 1 Anode

Figure 5. QE map of all the array at 600 nm, obtained by setting the hold-off time to 6 p.s.

Quantum Efficiency of Anode5,Cathoda4 element OverVoltaga 10%, 15%, 20%

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Wavelength [nm]

Figure 6. QE curves of the SPAD corresponding to anode 5, cathode 4 obtained by biasing at three overvoltage levels.

In Fig. 7 the QE values at 400, 600 and 800 nm are plotted versus biasing voltage (breakdown voltage plus overvoltage).

Figure 7. Plot of QE values at 400, 600 and 800 nm with respect to bias voltage (breakdown voltage plus overvoltage).

The QE value at a given wavelength increases with the SPAD bias voltage. It is evident from these plots that, in the selected range of voltages, we can simply derive the QE value (within an error of 5%) through a linear regression. Thus, by setting a bias voltage in a range of 28-31 V, we can predict the QE value with an uncertainty less than 5%.

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