Characterization of neutron transmutation doped (NTD) Ge for low temperature sensor development

TL;DR

This study characterizes neutron transmutation doped germanium for low-temperature sensors, focusing on defect analysis and recovery post-irradiation, to enable their use in mK thermometry for the TIN.TIN detector.

Contribution

It provides detailed defect characterization and demonstrates effective annealing procedures to restore irradiated Ge, advancing low-temperature sensor development.

Findings

Monovacancy defects identified by PALS in irradiated samples

No significant defects after fast neutron exposure at specified fluence

Vacuum annealing at 600°C for 2 hours recovers irradiation damage

Abstract

Development of NTD Ge sensors has been initiated for low temperature (mK) thermometry in The India-based Tin detector (TIN.TIN). NTD Ge sensors are prepared by thermal neutron irradiation of device grade Ge samples at Dhruva reactor, BARC, Mumbai. Detailed measurements have been carried out in irradiated samples for estimating the carrier concentration and fast neutron induced defects. The Positron Annihilation Lifetime Spectroscopy (PALS) measurements indicated monovacancy type defects for all irradiated samples, while Channeling studies employing RBS with 2 MeV alpha particles, revealed no significant defects in the samples exposed to fast neutron fluence of $\sim 4\times10^{16}/cm^2$. Both PALS and Channeling studies have shown that vacuum annealing at 600 $^\circ$C for $\sim2$ hours is sufficient to recover the damage in the irradiated samples, thereby making them suitable for the sensor development.