Abstract
Hyperdoped silicon with deep level impurities has attracted much research interest due to its promising optical and electrical properties. In this work, single crystalline silicon supersaturated with titanium is fabricated by ion implantation followed by both pulsed laser melting and flash lamp annealing. The decrease of sheet resistance with increasing Ti concentration is attributed to a surface morphology effect due to the formation of cellular breakdown at the surface and the percolation conduction at high Ti concentration is responsible for the metallic-like conductivity. The insulator-to-metal transition does not happen. However, the doping effect of Ti incorporation at low concentration is not excluded, which might be responsible for the sub-bandgap optical absorption reported in literature.
Highlights
Hyperdoping Si with deep level impurities is one of the most effective approaches to form an intermediate band (IB)
We have reported that the cellular breakdown takes place in Ti-implanted Si samples after pulsed laser annealing (PLA), but it can be effectively suppressed by millisecond-flash lamp annealing (FLA)[25]
The results prove that the crystal order, even in heavily implanted Si, can be well restored by both FLA and PLA
Summary
Hyperdoping Si with deep level impurities is one of the most effective approaches to form an intermediate band (IB). Insulator-to-metal transition (IMT) has been reported in S- and Se-hyperdoped silicon[6,11,12], which is a direct evidence for the formation of an IB. Titanium is another deep-level impurity candidate for forming an IB in Si13–15. The inhomogeneous distribution of Ti impurities complicates the interpretation of the electrical properties It still remains unclear whether the IMT in Ti-hyperdoped Si happens or not. After FLA, the samples remain insulating even with the highest Ti implantation fluence, whereas the sheet resistance decreases with increasing Ti concentration after PLA. According to the results from conductive atomic force microscopy (C-AFM), the decrease of the sheet resistance after PLA is attributed to the percolation of Ti-rich cellular walls and not the insulator-to-metal transition due to Ti-doping
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