On the nature and charge state of the X-Defect, a radiation-induced Silicon defect with field-enhanced charge carrier emission

TL;DR

This study identifies the radiation-induced X-Defect in low-resistivity p-type silicon as the singly positively charged silicon di-vacancy $ ext{V}_2(+/0)$, using advanced spectroscopy, simulations, and analysis of charge emission mechanisms.

Contribution

The paper provides the first comprehensive identification of the X-Defect as $ ext{V}_2(+/0)$, clarifying its charge state and emission process through combined experimental and simulation approaches.

Findings

X-Defect is identified as $ ext{V}_2(+/0)$.

Charge emission is dominated by phonon-assisted tunnelling.

The defect is neutral in the space charge region.

Abstract

The elusive X-Defect, a defect found in low-resistivity $p$-type Silicon after irradiation, observed as a low-temperature shoulder of the $\mathrm{B}_\mathrm{i}\mathrm{O}_\mathrm{i}$ defect (Boron-interstitial-Oxygen-interstitial complex) in Thermally Stimulated Current (TSC) measurements, was investigated to determine its properties, matching them with those of a previously identified defect. Through a combination of TSC, Deep-Level Transient Spectroscopy (DLTS), Difference-DLTS (DDLTS), numerical simulations of field-enhanced charge carrier emissions in TSC measurements and a comparison to literature, the X-Defect was identified as the singly positively charged Silicon di-vacancy $\mathrm{V}_2(+/0)$. This assignment is supported by an agreement in activation energy, capture cross-section, trap type and charge emission process, as well as simulations comparing the effects of phonon-assisted tunnelling (PAT) and Poole-Frenkel (PF) mechanisms on TSC spectra. DDTLS measurements revealed a quadratic dependence of the activation energy on the electric field strength, confirming PAT as the prevailing mechanism over PF in the case of the radiation-induced X-Defect. Assigning the X-Defect to an electrically neutral defect in the space charge region resolves previous contradictions regarding its deficiency in impacting on the effective doping concentration.