Development of NTD Ge for low temperature thermometry

The development of NTD Ge sensors for use in cryogenic bolometric detector to search for neutrinoless double beta decay (0νββ) in 124Sn is initiated [1]. The samples made from device grade Ge wafers are irradiated with thermal neutrons fluence in the range of 2 x 1018/cm2 to 1.4 x 1019/cm2 at Dhruva reactor, Bhabha Atomic Research Centre (BARC), Mumbai. The carrier concentration in irradiated Ge samples is estimated by Hall Effect measurement at 77K.The fast neutron induced defects are studied using Positron Annihilation Lifetime Spectroscopy and Channeling. It isfound that vacuum annealing of the samples at 600oC for2 hours is necessary to cure the defects. Sensors are made from annealed NTD Ge samples using Au-Ge Ohmic contact. Preliminary measurements have shown a significantly larged R/dT at mK temperature for the samples irradiated with the thermal neutron fluence in the range of 2 x 1018/cm2to 5 x 1018/cm2.  Samples irradiated with higher neutron fluence (>1019/cm2) have shown very low dR/dT. Details of these measurements will be presented in the talk.

References:
[1] 	Development of NTD Ge sensors for low temperature thermometry,    
S.Mathimalar et al., IEEE WOLTE conference, (2014) 
DOI: 10.1109/WOLTE.2014.6881014.