Evidence for vacancy trapping in Au-hyperdoped Si following pulsed laser melting

W Yang,A J Akey,Q Hudspeth,N Ferdous,P K Chow,J M Gaudet,J S Williams,E Ertekin,M J Aziz,P J Simpson,J M Warrender

doi:10.1063/1.5124709

Abstract

Nanosecond pulsed laser melting can be used to rapidly recrystallize ion-implanted Si through liquid phase epitaxy. The rapid resolidification that follows the melting results in a supersaturation of impurities and hyperdopes the Si, inducing novel optoelectronic properties with a wide range of applications. In this work, structural changes in the Si lattice in Au-hyperdoped Si are studied in detail. Specifically, we show that the local skewing of the lattice observed previously in regions of extremely high Au concentrations (&gt;1.4 at. %) can be related to the displacement of Au from perfect lattice positions. Surprisingly, although the incorporation of the larger Au atoms into Si is expected to cause swelling of the lattice, reciprocal space mapping shows that a small amount (0.3 at. %) of lattice contraction (decrease in lattice parameter) is present in the hyperdoped layer. Furthermore, positron annihilation spectroscopy shows an elevated concentration of vacancies in the hyperdoped layer. Based on these observations and with the aid of density functional theory, we propose a phenomenological model in which vacancies are kinetically trapped into lattice sites around substitutional Au atoms during resolidification. This vacancy trapping process is hypothesized to occur as a means to minimize lattice strain and may be universal in pulsed laser melted Si systems.

Highlights

Ion implantation followed by pulsed laser melting (PLM) is a well-known technique for incorporating impurities into Si, usually into substitutional lattice sites, at concentrations well in excess of the thermodynamic solubility limit.1 This nonequilibrium process, known as hyperdoping, has been used to realize unique compositional and structural regimes in Si,2,3 with diverse potential applications such as infrared photodetection,4 intermediate band photovoltaics,5 and superconductivity.6 While hyperdoped Si has been shown to exhibit good crystalline quality, the local lattice environment is modified by high concentrations of impurity atoms that are often larger than Si
We show that Au-hyperdoped Si exhibits a smaller out-of-plane lattice parameter compared with unstrained bulk Si and demonstrate how this contraction is directly related to the trapping of vacancies during resolidification following PLM
We have shown that Au atoms in hyperdoped Si fabricated using ion implantation and PLM reside on nearsubstitutional lattice sites but deviate slightly into the axis and reduce the lattice parameter of Si slightly

Summary

Introduction

Ion implantation followed by pulsed laser melting (PLM) is a well-known technique for incorporating impurities into Si, usually into substitutional lattice sites, at concentrations well in excess of the thermodynamic solubility limit. This nonequilibrium process, known as hyperdoping, has been used to realize unique compositional and structural regimes in Si, with diverse potential applications such as infrared photodetection, intermediate band photovoltaics, and superconductivity. While hyperdoped Si has been shown to exhibit good crystalline quality, the local lattice environment is modified by high concentrations of impurity atoms that are often larger than Si (usually in the order of a few atomic percent). Ion implantation followed by pulsed laser melting (PLM) is a well-known technique for incorporating impurities into Si, usually into substitutional lattice sites, at concentrations well in excess of the thermodynamic solubility limit.. Ion implantation followed by pulsed laser melting (PLM) is a well-known technique for incorporating impurities into Si, usually into substitutional lattice sites, at concentrations well in excess of the thermodynamic solubility limit.1 This nonequilibrium process, known as hyperdoping, has been used to realize unique compositional and structural regimes in Si, with diverse potential applications such as infrared photodetection, intermediate band photovoltaics, and superconductivity.. A negative out-of-plane strain (lattice contraction) has been consistently measured for laser-melted Si hyperdoped with B, As, and Sb.7–9 The latter two results are especially interesting, as the incorporation of As and Sb atoms should give rise to expansion of the lattice based on size considerations, since the covalent radii of both As (1.21 Å) and Sb (1.41 Å) are larger than the atomic radius of Si (1.17 Å). A negative out-of-plane strain (lattice contraction) has been consistently measured for laser-melted Si hyperdoped with B, As, and Sb. The latter two results are especially interesting, as the incorporation of As and Sb atoms should give rise to expansion of the lattice based on size considerations, since the covalent radii of both As (1.21 Å) and Sb (1.41 Å) are larger than the atomic radius of Si (1.17 Å).

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Conclusion