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

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 (>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.

Carrier Dynamics and Absorption Properties of Gold-Hyperdoped Germanium: Insight Into Tailoring Defect Energetics

“…Although Au energetically prefers substitutional sites in Ge [36], both substitutionals Au Ge and tetrahedral interstitials Au i,tetr are considered because the laser-implantation process may result in nonequilibrium defect distributions. In addition, there is evidence that ion implantation followed by PLM can leave behind a substantial, nonequilibrium population of vacancies that can trap or otherwise interact with the dopant atoms [19]. Therefore, we also consider complexes that may form between Au and vacancies.…”

“…Previous studies on hyperdoped systems were mainly focused on Si [12][13][14][15][16][17][18][19][20]. One carrier recombination study in chalcogen-hyperdoped Si reveals a decrease in lifetimes with increasing dopant concentrations [18].…”

“…One ongoing study of Au-hyperdoped Si (Si:Au) shows very short charge carrier lifetimes of the order of 10 ps [21], but another study reports sub-band-gap photodetection out to 2200 nm at room temperature [10]. Density functional theory (DFT) calculations have previously been applied to Si:Au to investigate the defect formation energy, band structure, and absorption coefficients [19,20]. The DFT results show that the substitutional Au defects in Si are more energetically favorable than the interstitials [20].…”

Electrical and Optical Doping of Silicon by Pulsed-Laser Melting

“…In other words, the Au substitutional dimer is not optically active. Furthermore, positron annihilation spectroscopy (PAS) measurements indicated that there is an elevated concentration of vacancies trapped along with Au following PLM, presumably to reduce the overall strain in Au-hyperdoped Si [86]. As shown in Figure 11, DFT predicted several Au-vacancy configurations that can form from PLM, and only some of which are optically active.…”

“…A major consequence of having a distribution of different substitutional/partly substitutional Au configurations in Au-hyperdoped Si is that the experimentally observed sub-bandgap optical absorption will be greatly suppressed [82,86]. Additionally, since the substitutional Au concentration measured from RBS-C is only about two to three times greater than N C , it is very likely that there is insufficient optically active Au in the Auhyperdoped Si samples to form a Au-induced IB.…”