Increase of the photoconductivity quantum yield in silicon irradiated by neutrons to extremely high fluences

Abstract

An enhanced quantum yield observed in silicon ionizing radiation detectors, neutron-irradiated to extremely high fluences, could be attributed to impact ionization via deep levels. The quantum yield was investigated by the intrinsic photoconductivity optical spectroscopy in silicon irradiated by neutrons to a wide range of fluences up to 1×1017neutron/cm2. An increase of quantum yield was observed in highly irradiated samples. We have demonstrated that the quantum yield enhancement could be attributed to the impact ionization via deep levels, this process being presumably related to disordered defect clusters regions in Si. The proposed mechanism explains the observed decrease of the impact ionization energy by at least an order of magnitude at low temperature. The impact ionization energy values of up to 0.30-0.36 eV and less, and 0.38-0.40 eV were determined at T~21-33 K and at T=195 K, respectively.

Increase of the surface recombination velocity at high bias voltage in silicon irradiated by neutrons to extremely high fluences

“…The observed threshold of the quantum yield increase with the photon energy took place at much lower energy than it was observed earlier; therefore, it was necessary to develop a new model of the impact multiplication of free electrons [1,[12][13], and this effect was observed only in the samples irradiated by neutron fluence above 10 15 neutron/cm 2 . It was proposed that it was related to the properties of the cluster created by high energy hadrons [14,15].…”

“…We have investigated the same Si samples as in Ref. [1]. They were fabricated by the magnetic Czochralski (MCZ) method.…”

“…The increase of the quantum yield was analyzed in Ref. [1]. The increase of the surface recombination with bias electric field was analyzed in this work as an extension of the performed investigation in the same samples as in Ref.…”

“…Also, the increase of quantum yield data is presented in the samples that were analyzed in Ref. [1], but in this paper we present data only in the samples that are biased with a high voltage.…”

“…The increase of the surface recombination with bias electric field was analyzed in this work as an extension of the performed investigation in the same samples as in Ref. [1]. The investigated silicon samples were irradiated by neutrons to wide range fluence up to 10 17 n/cm 2 .…”