Nanosecond-laser hyperdoping of intrinsic silicon to modify its electrical and optical properties

Pulsed-laser melting of thin films has attracted increasing attention for manufacturing hyperdoped semi-conductors as photovoltaic materials. However, most of the research on pulsed-laser melting of thin films has been focused on the femtosecond-laser hyperdoping, leaving the process and mechanism of nanosecond-laser (ns-laser) hyperdoping largely unexplored. Therefore, high-resistivity (>10(4) Omega center dot cm) intrinsic Si wafers were hyper-doped with Ti via thin Ti film deposition and ns-laser melting. Thus, the bulk carrier concentration and resistivity of the Ti-hyperdoped Si (Si:Ti) layer reached -2.60 x 10(20) cm(-3) and 3.7 x 10(-3) Omega center dot cm, respectively. Furthermore, the infrared absorptance of the Si:Ti layer increased to similar to 63% in the wavelength range of 1100-2500 nm, which was much higher than that of intrinsic Si crystal (-0%). In addition, the Si:Ti layer showed a nanocrystalline structure, and its average depth increased from 230 to 515 nm with the increase of Ti film thickness from 60 to 150 nm and ns-laser fluence from 2.27 to 2.70 J center dot cm(-2). Meanwhile, Ti impurities were fully distributed in these Si:Ti layers. The normalized concentrations of Ti increased from 2.4 at. % to 7.4 at. %. Moreover, the high concentrations of Ti impurity atoms chemically bound with Si atoms formed a TiSi2 phase. Finally, the ns-laser hyperdoping mechanism was proposed as follows. During the ns-laser irradiation, the Ti films were melted at first, and a large part of laser heat was transferred to the intrinsic Si substrate surface to form Ti and Si molten mixed layers. Then, the heat promoted the incorporation of Ti into the Si lattice, forming bonds. Finally, the Si:Ti layer was formed via resolidification and crystallization after ns-laser treatment.

Automated summary

Pulsed-laser melting of thin films has been widely studied for hyperdoping semiconductors, but the focus has mainly been on femtosecond-laser hyperdoping rather than nanosecond-laser hyperdoping. In this study, high-resistivity intrinsic Si wafers were hyperdoped with Ti through thin Ti film deposition and ns-laser melting. The resulting Si:Ti layer showed high carrier concentration, low resistivity, and increased infrared absorptance.