B-Doped δ-Layers and Nanowires from Area-Selective Deposition of BCl₃ on Si(100)

Atomically precise, δ-doped structures forming electronic devices in Si have been routinely fabricated in recent years by using depassivation lithography in a scanning tunneling microscope (STM). While H-based precursor/monatomic resist chemistries for incorporation of donor atoms have dominated these efforts, the use of halogen-based chemistries offers a promising path toward atomic-scale manufacturing of acceptor-based devices. Here, B-doped δ-layers were fabricated in Si(100) by using BCl₃ as an acceptor dopant precursor in ultrahigh vacuum. Additionally, we demonstrate compatibility of BCl₃ with both H and Cl monatomic resists to achieve area-selective deposition on Si. In comparison to bare Si, BCl₃ adsorption selectivity ratios for H- and Cl-passivated Si were determined by secondary ion mass spectrometry depth profiling (SIMS) to be 310(10):1 and 1529(5):1, respectively. STM imaging revealed that BCl₃ adsorbed readily on bare Si at room temperature, with SIMS measurements indicating a peak B concentration greater than 1.2(1) × 10²¹ cm^-3 with a total areal dose of 1.85(1) × 10¹⁴ cm^-2 resulting from a 30 langmuir BCl₃ dose at 150 °C. In addition, SIMS showed a δ-layer thickness of ∼0.5 nm. Hall bar measurements of a similar sample were performed at 3.0 K, revealing a sheet resistance of ρ_□ = 1.9099(4) kΩ □^-1, a hole carrier concentration of p = 1.90(2) × 10¹⁴ cm^-2, and a hole mobility of μ = 38.0(4) cm² V^-1 s^-1 without performing an incorporation anneal. Finally, 15 nm wide B δ-doped nanowires were fabricated from BCl₃ and were found to exhibit ohmic conduction. This validates the use of BCl₃ as a dopant precursor for atomic-precision fabrication of acceptor-doped devices in Si and enables development of simultaneous n- and p-type doped bipolar devices.