Abstract
Doping via self-assembled macromolecules might offer a solution for developing single atom electronics by precisely placing individual dopants at arbitrary location to meet the requirement for circuit design. Here we synthesize dendrimer-like polyglycerol macromolecules with each carrying one phosphorus atom in the core. The macromolecules are immobilized by the coupling reagent onto silicon surfaces that are pre-modified with a monolayer of undecylenic acid. Nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS) are employed to characterize the synthesized macromolecules and the modified silicon surfaces, respectively. After rapid thermal annealing, the phosphorus atoms carried by the macromolecules diffuse into the silicon substrate, forming dopants at a concentration of 1017 cm−3. Low-temperature Hall effect measurements reveal that the ionization process is rather complicated. Unlike the widely reported simple ionization of phosphorus dopants, nitrogen and carbon are also involved in the electronic activities in the monolayer doped silicon.
Highlights
Placing individual dopants at arbitrary location is critical for single atom electronics[1] and sub-nanometer integrated circuits[1,2]
To reduce the carbon defects, we developed a new process by annealing the sample in O2 at 550 °C for 5 hours, right before the rapid thermal annealing at 1050 °C
The macromolecules each carrying one phosphorus atom in the core are immobilized on the silicon surface by forming covalent bonds with the pre-modified silicon surfaces
Summary
Process, the molecular molar ratio of glycerol to tris(4-methoxyphenyl)phosphine oxide was set to 450:1 to reach the size of up to several nanometers in diameter for polyglycerol as shown in the literature reports[16]. A similar ratio (0.98) has been observed for silicon surfaces modified only with undecylenic acid monolayers (SI Fig. S8). This observation indicates that nearly no polyglycerol molecules are bonded onto the control sample surfaces (without DCC). A large quantity of nitrogen is still observed in the sample and the ionization rate of phosphorus continues to remain low In this case, the source of nitrogen is mostly likely from the physical absorption of N2 from the air since nitrogen is detected near the surface of as-purchased intrinsic silicon substrate (see SI Fig. S22 and the related discussions). Low-temperature Hall measurements were conducted on the sample, revealing a significantly improved ionization rate of phosphorus (see SI Fig. S23)
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