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STM study of single phosphorus incorporation into silicon by heating PBr3 on Si(100)

2026 · ARTICLE · en

The objective of miniaturizing doped areas in silicon, with the ultimate goal of achieving atomic-precision doping, requires a fundamental understanding of the dopant incorporation process at the atomic level. We present a combined scanning tunneling microscopy (STM) and density functional theory (DFT) investigation of single phosphorus atom incorporation into the Si(100) surface. Phosphorus was supplied via PBr molecules, which completely dissociate on Si(100) at room temperature. By performing in situ annealing within the STM, we directly tracked the same phosphorus atom before and after heating. Upon annealing, the P atom undergoes an exchange with a nearby Si atom, forming a stable P–Si–Br complex with a Br atom located atop the Si atom of the heterodimer. The activation barrier calculated using DFT is consistent with our observation of doping starting at temperatures as low as 175 °C. These results provide detailed atomic-scale insight into the phosphorus incorporation pathway and offer a foundation for improving methods of precise, single-atom doping in silicon.

Calculations of pathways of precise P incorporation into chlorinated Si(100) surface

2025 · ARTICLE · en

Surface diffusion of phosphorus on Si(100) after PBr3 adsorption

2025 · ARTICLE · en

Phosphorus diffusion on a Si(100) surface was studied using scanning tunneling microscopy (STM) at temperatures of 77 and 300 K. The phosphorus source utilized was the PBr_3 molecule, which fully dissociates on the surface at 77 K. We observed diffusion of P atoms both along and across the rows of Si dimers. To support the observation of different diffusion pathways of phosphorus, activation energy calculations were performed using density functional theory. At 77 K, phosphorus diffusion started and (or) finished mostly in bridge positions. At 300 K, phosphorus diffuses predominantly between end-bridge positions, accompanied by bromine diffusion. The presence of Br near phosphorus significantly restricts its mobility. Additionally, phosphorus was found to diffuse to an oxygen atom that appeared on the surface as a result of water adsorption. This diffusion occurs because the P site near the oxidized dimer is more stable compared to that on the clean surface. The obtained results complement the knowledge about the interaction of phosphorus with the silicon surface, specifically the phosphorus diffusion pathways on the Si(100) surface.

PBr3 adsorption on a chlorinated Si(100) surface with mono- and bivacancies

2024 · ARTICLE · en

For the most precise incorporation of single impurities in silicon, which is utilized to create quantum devices, a monolayer of adatoms on the Si(100) surface and a dopant-containing molecule are used. Here we studied the interaction of a phosphorus tribromide with a chlorine monolayer with mono- and bivacancies in a scanning tunneling microscope (STM) at 77 K. The combination of different halogens in the molecule and the adsorbate layer enabled unambiguous identification of the structures after PBr3 dissociation on Si(100)-Cl. A Cl monolayer was exposed to PBr3 in the STM chamber, which allows us to compare the same surface areas before and after PBr3 adsorption. As a result of this comparison, we detected small changes in the chlorine layer and unraveled the molecular fragments filling mono- and bivacancies. Using density functional theory, we found that the phosphorus atom occupies a bridge position after dissociation of the PBr3 molecule, which primarily bonds to silicon in Cl bivacancies. These findings provide insight into the interaction of a dopant containing molecule with an adsorbate monolayer on Si(100) and can be applied to improve the process of single impurities incorporation into silicon.

PBr3 Adsorption and Dissociation on the Si(100) Surface

2023 · ARTICLE · en

The adsorption of PBr3 on the Si(100)-2 × 1 surface was studied by scanning tunneling microscopy (STM) and density functional theory (DFT). The PBr3 molecule completely dissociates on the Si(100) surface at room temperature into P and Br atoms. In most cases, the dissociated molecule was observed in STM on three neighboring Si dimers. DFT calculations confirm that the PBr3 molecule can completely dissociate at room temperature. After annealing the sample to 400 °C, phosphorus is incorporated into silicon, as evidenced by the Si atoms ejected to the surface. These findings are useful for the insertion of individual phosphorus atoms into silicon by PBr3 adsorption through a halogen mask.

Enhancing the reactivity of Si(100)–Cl toward PBr3 by charging Si dangling bonds

2023 · ARTICLE · en

The interaction of the PBr3 molecule with Si dangling bonds (DBs) on a chlorinated Si(100) surface was studied. The DBs were charged in a scanning tunneling microscope (STM) and then exposed to PBr3 directly in the STM chamber. Uncharged DBs rarely react with molecules. On the contrary, almost all positively charged DBs were filled with molecule fragments. As a result of the PBr3 interaction with the positively charged DB, the molecule dissociated into PBr2 and Br with the formation of a Si–Br bond and PBr2 desorption. These findings show that charged DBs significantly modify the reactivity of the surface toward PBr3. Additionally, we calculated PH3 adsorption on a Si(100)–2 × 1–H surface with DBs and found that the DB charge also has a significant impact. As a result, we demonstrated that the positively charged DB with a doubly unoccupied state enhances the adsorption of molecules with a lone pair of electrons.

Dangling bonds on the Cl- and Br-terminated Si(100) surfaces

2022 · ARTICLE · en

Halogen monolayer on a silicon surface is attracting active attention for applications in electronic device fabrication with individual impurities. To create a halogen mask for the impurities incorporation, it is desirable to be able to remove a single halogen atom from the surface. We report the desorption of individual halogen atoms from the Si(100)-2 × 1-Cl and -Br surfaces in a scanning tunneling microscope (STM). Silicon dangling bonds (DBs) formed on the Si surface after halogen desorption were investigated using STM and the density functional theory. Three charge states: positive, neutral, and negative were identified. Our results show that the charge states of DBs can be manipulated, which will allow to locally tune the reactivity of the Cl- and Br-terminated Si(100) surfaces.

Vacancy diffusion on a brominated Si(100) surface: Critical effect of the dangling bond charge state

2022 · ARTICLE · en

Silicon dangling bonds (DBs) on an adsorbate-covered Si(100) surface can be created in a scanning tunneling microscope (STM) with high precision required for a number of applications. However, vacancies containing DBs can diffuse, disrupting precisely created structures. In this work, we study the diffusion of Br vacancies on a Si(100)-2 × 1-Br surface in an STM under typical imaging conditions. In agreement with previous work, Br vacancies diffuse at a positive sample bias voltage. Here, we demonstrated that only vacancies containing a positively charged DB hop across the two atoms of a single Si dimer, while vacancies containing neutral and negatively charged DBs do not. Calculations based on density functional theory confirmed that positively charged Br (and Cl) vacancies have a minimum activation barrier. We propose that diffusion operates by both one-electron and two-electron mechanisms depending on the applied voltage. Our results show that the DB charge has a critical effect on the vacancy diffusion. This effect should be taken into account when imaging surface structures with charged DBs as well as when studying the diffusion of other atoms and molecules on the Si(100) surface with vacancies in an adsorbate layer.

Dangling bonds on the Cl- and Br-terminated Si(100) surfaces

2022 · ARTICLE · en

Halogen monolayer on a silicon surface is attracting active attention for applications in electronic device fabrication with individual impurities. To create a halogen mask for the impurities incorporation, it is desirable to be able to remove a single halogen atom from the surface. We report the desorption of individual halogen atoms from the Si(100)-2 × 1-Cl and -Br surfaces in a scanning tunneling microscope (STM). Silicon dangling bonds (DBs) formed on the Si surface after halogen desorption were investigated using STM and the density functional theory. Three charge states: positive, neutral, and negative were identified. Our results show that the charge states of DBs can be manipulated, which will allow to locally tune the reactivity of the Cl- and Br-terminated Si(100) surfaces.

Reactivity of the Si(100)-2×1-Cl surface with respect to PH3, PCl3, and BCl3: Comparison with PH3 on Si(100)-2×1-H

2021 · ARTICLE · en

Despite the interest in a chlorine monolayer on Si(100) as an alternative to hydrogen resist for atomic-precision doping, little is known about its interaction with dopant-containing molecules. We used the density functional theory to evaluate whether a chlorine monolayer on Si(100) is suitable as a resist for PH3, PCl3, and BCl3 molecules. We calculated reaction pathways for PH3, PCl3, and BCl3 adsorption on a bare and Cl-terminated Si(100)-2 × 1 surface, as well as for PH3 adsorption on H-terminated Si(100)-2 × 1, which is widely used in current technologies for atomically precise doping of Si(100) with phosphorus. It was found that the Si(100)-2 × 1-Cl surface has a higher reactivity toward phosphine than Si(100)-2 × 1-H, and, therefore, unpatterned areas are less protected from undesirable incorporation of PH3 fragments. On the contrary, the resistance of the Si(100)-2 × 1-Cl surface against the chlorine-containing molecules turned out to be very high. Several factors influencing reactivity are discussed. The results reveal that phosphorus and boron trichlorides are well-suited for doping a patterned Cl-resist by donors and acceptors, respectively.