The study of the passivation technology for bare HPGe detector working in LN2

The direct operation of bare high purity germanium (HPGe) in liquid nitrogen (LN2) is a desirable method for rare event detection. However, how to improve the long-term stability of the HPGe detectors in this working condition is still worth exploring. In this study, a method combining chemical treatment (methanol passivation) with thin film deposition (SiOx films passivation) has been applied to the HPGe detector intercontact surface. As a result, the leakage current of the bare detector stabilized at the level of 1 pA (applied voltage up to 3600 V, depletion voltage of 1800 V) while it had been immersed in LN2 for more than six months. It shows that the surface passivation technology raised by this work can reliably protect the HPGe detector from environmental impact, which is very helpful to obtaining a stable HPGe detector with ultra-low leakage current.