Carrier lifetimes in gold–hyperdoped silicon—Influence of dopant incorporation methods and concentration profiles

Abstract

Incorporating ultrahigh concentrations of deep-level dopants in silicon drastically alters silicon’s optoelectronic properties. Photodiodes built from silicon hyperdoped with gold extend light sensitivity into the shortwave infrared region, far beyond the absorption edge of a pristine silicon sample. Deep-level dopants, however, also enhance carrier recombination; even though hyperdoped silicon has great light absorption properties, short charge carrier lifetime limits its applications. In this work, using terahertz spectroscopy, we investigate the charge carrier lifetime of gold–hyperdoped silicon, where the gold dopants are introduced by either film deposition or ion implantation, followed by pulsed laser melting. Using reactive ion etching, we measure how carrier lifetime changes when dopant concentration profiles are altered. Furthermore, using a 1D diffusion and recombination model, we simulate carrier dynamics when electrons are excited by sub-bandgap light. Our results show that the dopant distribution profile heavily influences excited carrier dynamics. We found that etching improves the half-life by a factor of two. In the short-wave-infrared range, the gold dopants are both light absorption centers and recombination centers. Focusing on optoelectronic properties in the short-wave-infrared region, our results suggest that these samples are over doped—etching much of the gold dopants away has little impact on the number of excited electrons at a later time. Our results suggest that dopant profile engineering is important for building efficient optoelectronic devices using hyperdoped semiconductors.

Cellular breakdown and carrier lifetimes in gold-hyperdoped silicon

“…Because of the inhomogeneous nature of the broken-down region, it is generally assumed that such breakdown of the hyperdoped material will be detrimental to electronic transport properties, such as carrier lifetime and mobility, sheet resistance, or even contact resistance; as well as optoelectronic properties, such as photoresponse or absorption coefficient. Carrier lifetime measurements of Au in Si for etched and/or passivated layers have recently been reported [18], but, to date no systematic study of the effects of breakdown on electronic properties has been undertaken. In this paper, we examine the cellular breakdown in Si hyperdoped with Au implanted at doses ranging from 1-10 × 10 15 at cm −2 , and present THz carrier lifetime measurements and device measurements to quantify the optoelectronic characteristics of materials that exhibit cellular breakdown.…”