Atomistic simulations of acceptor removal in p-type Si irradiated with neutrons

Pedro López,María Aboy,Irene Muñoz,Iván Santos,Luis A Marqués,Pablo Fernández-Martínez,Miguel Ullán,Lourdes Pelaz

doi:10.1016/j.nimb.2021.12.003

Abstract

The effective dopant concentration in p-type Si detectors reduces with irradiation fluence at low fluences due to the acceptor removal process, which degrades detector performance and shortens its lifetime. This effect has been experimentally characterized and parametrized, but its microscopic origin is still unknown. We use atomistic simulations to gain insight into acceptor removal in neutron irradiation by modeling damage generation and defect-dopant interactions. We analyze the effect on dopant deactivation of the Si di- and tri-interstitial diffusion, the inhomogeneity of irradiation damage and the wafer temperature rise during irradiation. We characterize defect generation rates and identify the relevant defect-dopant interactions. Acceptor removal occurs mainly through the formation of Bi pairs and small boron-interstitial clusters, and it is limited by the availability of mobile Si interstitials. The presence of impurities (O, C) modifies B-complexes favoring the formation of BiO, but has a limited effect on the amount of removed acceptors.

Highlights

Electronic devices operating in harsh radiative environments such as particle colliders and aerospace or nuclear applications must withstand high radiation fluences without functionality degradation
A phenomenological description of the acceptor removal process is commonly done through a set of first order reactions between defects, dopants and impurities, using several fitting parameters that account for the amount of generated defects and the probability of defect-dopant interactions [7,8,9]
It must be remarked that, contrary to the phenomenolog ical description of acceptor removal, our model considers all reactions leading to the formation and growth of boron-interstitial pair (Bi) and boron-interstitial clusters (BICs) with any stoichi ometry, providing a full atomistic description of defect-dopant interactions

Summary

Introduction

Electronic devices operating in harsh radiative environments such as particle colliders and aerospace or nuclear applications must withstand high radiation fluences without functionality degradation. The exposure of ptype detectors to radiation results in the reduction of the effective dopant concentration (Neff) with fluence at low fluences [4]. This effect is attributed to an acceptor removal process (dopant deactivation) caused by the interaction of radiation-induced defects with B atoms [5]. Neff values are mostly determined from depletion voltage measurements [6] This is a measure of the space charge distribution, which reflects the concentration of active dopants that contribute as shallow acceptors, and the presence of electrically active defects. We use atomistic simulations to analyze the acceptor removal in neutron irradiated p-type Si by modeling damage generation and dopant deactivation process. We analyze the main physical mechanisms responsible for dopant deactivation and provide clues to correctly describe the acceptor removal process at atomistic level

Experimental setup and simulation model

Modeling of acceptor removal

Neutron irradiation damage

B deactivation mechanisms and the role of O and C

Findings

Conclusions