Characterization of Ge detectors' passivation surface for LEGEND using Kr

The LEGEND experiment is searching for neutrinoless double beta decay in ⁷⁶Ge using arrays of high purity enriched Ge crystals. Each element of these arrays is a Ge diode weighing ~1 kg, with a nominal 1 μm thick passivation surface made up of non-crystalline Ge situated around the contact point of the detectors. However, the low energy spectrum from Majorana Demonstrator has revealed that the effective thickness of these layers is larger than expected, which may cause bleeding of high energy α particles into the Q_ββ region of interest of the experiment. A test-stand is set up at University of Washington, in joint collaboration with Indiana University, to investigate the effect of the effective thickness of the passivation surface using Kr as a low-energy mono-energetic electron source. Recent results from this have been able to reproduce the similar energy degradation in that passivation surface like Majorana. In this talk, I will present those results and also discuss a surface charge model which is showing promises at modifying the effective dead layer to explain this data.