Au-rich filamentary behavior and associated subband gap optical absorption in hyperdoped Si

Abstract

Au-hyperdoped Si, synthesized by ion implantation and pulsed laser melting, is known to exhibit a strong sub-band gap photoresponse that scales monotonically with the Au concentration. However, there is thought to be a limit to this behavior since ultrahigh Au concentrations (>1 × 10 20 cm −3) are expected to induce cellular breakdown during the rapid resolidification of Si, a process that is associated with significant lateral impurity precipitation. This work shows that the cellular morphology observed in Au-hyperdoped Si differs from that in conventional, steady-state cellular breakdown. In particular, Rutherford backscattering spectrometry combined with channeling and transmission electron microscopy revealed an inhomogeneous Au distribution and a subsurface network of Au-rich filaments, within which the Au impurities largely reside on substitutional positions in the crystalline Si lattice, at concentrations as high as ∼3 at. %. The measured substitutional Au dose, regardless of the presence of Au-rich filaments, correlates strongly with the sub-band gap optical absorptance. Upon subsequent thermal treatment, the supersaturated Au forms precipitates, while the Au substitutionality and the sub-band gap optical absorption both decrease. These results offer insight into a metastable filamentary regime in Au-hyperdoped Si that has important implications for Si-based infrared optoelectronics.

Room‐Temperature Infrared Photoresponse from Ion Beam–Hyperdoped Silicon

“…In this regard, several studies have been reported focusing on the changes of optoelectronic properties upon thermal treatment. [ 41,45,55,61,67 ]…”

“…The findings in the aforementioned works [ 45,55,58,61 ] suggest that a metastable local atomistic configuration of deep‐level impurity atoms in the Si host is responsible for the sub‐bandgap absorption. There is a one‐to‐one correlation between the substitutional deep‐level impurities and the unique properties.…”

“…By using Rutherford backscattering spectrometry combined with channeling, Yang et al [ 45 ] found that the substitutional fraction of Au atoms in Au‐hyperdoped Si layers dramatically decreases upon postannealing treatments at temperatures higher than 400 °C for only 3 min. Consequently, the sub‐bandgap optical absorption decreases.…”

“…[33] Alternatively, another transition metal, Au, has also been shown to be adequate for the IB formation within the Si bandgap. [34,45] An Au-hyperdoped Si photodetector exhibiting a room-temperature photoresponse up to 2.2 μm has been demonstrated (see Table 2). Importantly, the sub-bandgap optical activity in Au-hyperdoped Si increases monotonically with the Au implantation dose.…”

“…In this regard, several studies have been reported focusing on the changes of optoelectronic properties upon thermal treatment. [41,45,55,61,67] By using Rutherford backscattering spectrometry combined with channeling, Yang et al [45] found that the substitutional fraction of Au atoms in Au-hyperdoped Si layers dramatically decreases upon postannealing treatments at temperatures higher Figure 3. a) Cross-sectional high-angle annular dark-field scanning transmission electron microscopy image superimposed with the corresponding energy-dispersive X-ray spectroscopy element maps (blue: Te, green: Si, red: O) for the PLA-treated Te-hyperdoped Si layer (Te-1.5%); b) representative high-resolution transmission electron microscopy image with the corresponding fast-Fourier transform pattern (inset) for a field of view as shown by the red square in the image part (a); c) room-temperature sub-bandgap optical absorptance spectra from the PLA-treated Te-hyperdoped Si samples with different Te concentrations.…”