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

Abstract

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 82 Se and 100 Mo using ZnSe and ZnMoO 4 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 SiO 2 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.

The CUPID-Mo experiment for neutrinoless double-beta decay: performance and prospects

“…The high-purity Ge wafers (Umicore Electro-Optical Material, Geel, Belgium), used as absorbers for the scintillation light, have a diameter of 44.5 mm and a 175 µm thickness. A ∼70 nm SiO coating was evaporated on both sides of the Ge wafer to make them opaque, thus increasing the light collection by ∼35% [35]. A small part of the wafer surface was left uncoated to ease the gluing of a temperature sensor.…”

Development of $$^{100}\hbox {Mo}$$ 100 Mo -containing scintillating bolometers for a high-sensitivity neutrinoless double-beta decay search

“…All of them are based on high purity Ge wafers and their typical size is 44-45 mm in diameter and 0.17-0.3 mm thickness, but two detectors have slightly lower area and tens µm thickness. Some light detectors were constructed according to the LU-MINEU standard described in [58], with the additional deposition of a 70 nm SiO antireflecting coating on one surface of the Ge wafer to increase the light absorption [59]. Another type of light detectors used in the present study was developed by the LUCIFER group [60].…”

Low background techniques in bolometers for double-beta decay search

“…63,87,[186][187][188][189] Consequently, the light collection efficiency is crucial for detectors with low light yield, thus the study of light production and transport, as e.g., 190 are rather important for the detector optimization. In particular, the light collection can be enhanced by improving the material quality (transmittance to the emitted light), by choosing a proper crystal shape and surface treatment, 102,191,192 by reducing the light reflection in the photodetector, [193][194][195] by adding an efficient reflector, 41,63 as well as by using an optical bolometer with an area comparable to a crystal-side surface. 41, 63…”