Incorporation of gold into silicon by thin film deposition and pulsed laser melting

Abstract

We report on the incorporation of gold into silicon at a peak concentration of 1.9 × 1020 at./cm3, four orders of magnitude above the equilibrium solubility limit, using pulsed laser melting of a thin film deposited on the silicon surface. We vary the film thickness and laser process parameters (fluence, number of shots) to quantify the range of concentrations that can be achieved. Our approach achieves gold concentrations comparable to those achieved with ion implantation followed by pulsed laser melting, in a layer with high crystalline quality. This approach offers an attractive alternative to ion implantation for forming high quality, high concentration layers of transition metals like gold in silicon.

Observation of enhanced infrared absorption in silicon supersaturated with gold by pulsed laser melting of nanometer-thick gold films

“…The similarity of absorptance profiles for the ion-implanted and thin-film hyperdoped samples suggests that the sub-bandgap absorption in the 1-nm case is due to the substitutional donor-to-conduction band transition previously observed in Au-hyperdoped Si. 9 Our prior secondary ion-mass spectrometry (SIMS) measurements of Au concentration versus depth confirmed that PLM of a thin Au film can achieve comparable supersaturated concentrations in Si, 14 further supporting the argument that Au is responsible for inducing electronic states that enhance the infrared absorption of Si. Near the Si band edge, the Audoped Si sub-bandgap absorptance increases towards shorter wavelengths as compared to PLM-treated sulfur-implanted p-Si 4 [dashed pink curve in Fig.…”

“…We observed clear rectification in the diode. Therefore, assuming that the hyperdoped film is electronically isolated, due to the rectifying junction formation, a material resistivity of $0.3-0.6 X cm was calculated by assuming a 50-100 nm thick Si:Au layer (based on prior SIMS measurements 14 ). This thickness corresponds to the depth where the Au concentration exceeds 10 18-19 cm À3 .…”

“…Despite successful junction formation, the anomalously high (n > 2) ideality factor could be a result of the finite contact resistance between titanium and the 1-nm Au-doped Si layer, 26 a characteristic feature of carrier recombination in heavily gold-supersaturated Si or the result of a non-abrupt p-n junction due to the tail of the gold concentration profile. 14 We employed a simpler contacting procedure for studying the 5-and 10-nm film samples' electrical behavior. Although exposure to elevated processing temperatures not exceeding 300 C was assumed to not significantly alter the properties of the 1 nm Au film-doped samples, based on our absorptance, Raman and RBS data, we could not safely assume this for the 5-and 10-nm Au film samples due to their relative thermal instability.…”

“…Gold, having one of the smallest diffusive velocities of the transition metals, was proposed as a plausible candidate impurity due to the ability of PLM to kinetically trap large atomic concentrations ($10 18 -10 22 cm À3 ) in Si through ion implantation and PLM, 9,10 as well as using PLM of vapordeposited thin (1-10 nm) Au films on Si. 14 The latter approach reduces fabrication complexity and eliminates the necessity to melt beyond the amorphisation or damaged layer as in the case of ion implantation. 10 The technological promise of Au-hyperdoped Si prepared by ion implantation and PLM was demonstrated when an absorption coefficient, a, of $600 cm À1 at k ¼ 1550 nm (Ref.…”

Influence Of Dopant Concentration Profiles On Charge Carrier Lifetimes In Gold Hyperdoped Silicon

“…Gold has been found to be a promising candidate as a dopant [6] and is the element we consider in this study. Hyperdoping can increase the efficiency of silicon solar cells because dopants create an intermediate band (IB) between the valence and conduction bands, so the solar cells can capture a broader range of light (Figure 1.3).…”