Is the gain-voltage dependence of SiPMs linear?

Abstract

The gain-voltage dependence for SiPMs from V. Chmill et al., Study of the breakdown voltage of SiPMs, is reanalyzed and a non-linearity at the sub-percent level is observed. Simulations show that he non-linearity can be explained by the increase of the depletion depth of the avalanche region with over-voltage. A consequence of the non-linearity is that the voltage at which the discharge stops is systematically underestimated if a linear extrapolation is used. However, the shift is too small to explain the difference between the break-down voltage from the current-voltage dependence and the one obtained from the extrapolation of the gain-voltage dependence to gain one. The results are confirmed by measurement of a different MPPC produced by Hamamatsu which has a break-down voltage which is about a factor two higher.