An experimental study of antireflective coatings in Ge light detectors for scintillating bolometers

¹ Centre de Spectrométrie Nuclaire et de Spectrométrie de Masse, CNRS and Université Paris-Sud, F-91405 Orsay, France
² Università dell’Insubria, Dipartimento di Scienza e Alta Tecnologia, 22100 Como, Italy
³ Lawrence Berkeley National Laboratory, Berkeley, CA94720, USA
⁴ INFN, Sezione di Milano Bicocca, 20126 Milano, Italy
⁵ Università di Milano-Bicocca, Dipartimento di Fisica

^a e-mail: michele.mancuso@csnsm.in2p3.fr

Published online: 10 January 2014

Abstract

Luminescent bolometers are double-readout devices able to measure simultaneously the phonon and the light yields after a particle interaction in the detector. This operation allows in some cases to tag the type of the interacting quantum, crucial issue for background control in rare event experiments such as the search for neutrinoless double beta decay and for interactions of particle dark matter candidates. The light detectors used in the LUCIFER and LUMINEU searches (projects aiming at the study of the double beta interesting candidates ⁸²Se and ¹⁰⁰Mo using ZnSe and ZnMoO₄ scintillating bolometers) consist of hyper-pure Ge thin slabs equipped with NTD thermistors. A substantial sensitivity improvement of the Ge light detectors can be obtained applying a proper anti-reflective coatings on the Ge side exposed to the luminescent bolometer. The present paper deals with the investigation of this aspect, proving and quantifying the positive effect of a SiO₂ and a SiO coating and setting the experimental bases for future tests of other coating materials. The results confirm that an appropriate coating procedure helps in improving the sensitivity of bolometric light detectors by an important factor (in the range 20% – 35%) and needs to be included in the recipe for the development of an optimized radio-pure scintillating bolometer.