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

Abstract

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 BCl 3 as an acceptor dopant precursor in ultrahigh vacuum. Additionally, we demonstrate compatibility of BCl 3 with both H and Cl monatomic resists to achieve area-selective deposition on Si. In comparison to bare Si, BCl 3 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 BCl 3 adsorbed readily on bare Si at room temperature, with SIMS measurements indicating a peak B concentration greater than 1.2(1) × 10 21 cm −3 with a total areal dose of 1.85(1) × 10 14 cm −2 resulting from a 30 langmuir BCl 3 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) × 10 14 cm −2 , and a hole mobility of μ = 38.0(4) cm 2 V −1 s −1 without performing an incorporation anneal. Finally, 15 nm wide B δ-doped nanowires were fabricated from BCl 3 and were found to exhibit ohmic conduction. This validates the use of BCl 3 as a dopant precursor for atomicprecision fabrication of acceptor-doped devices in Si and enables development of simultaneous n-and p-type doped bipolar devices.

Hole in one: Pathways to deterministic single-acceptor incorporation in Si(100)-2$\times$1

“…We next turn to boron trichloride (BCl 3 ), which has recently been demonstrated to have excellent acceptor doping properties in δ-doped layers [28]. In contrast to diborane, boron trichloride exhibits a drastically simplified reaction pathway as demonstrated by Dwyer et al [65], with only three possible steps and a likely reaction barrier of 0.93 eV.…”

“…Single shallow dopants placed with atomic precision in silicon might be used to realize qubits [1][2][3][4][5][6][7][8][9][10], single-tofew-carrier devices [11][12][13][14][15][16][17], and analog quantum simulators [18][19][20][21][22]. While the placement of phosphorus donors using a phosphine (PH 3 ) precursor has received the most development [23][24][25], recent demonstrations involving arsenic [26], boron [27,28], and aluminum [29,30] indicate that the breadth of viable chemistries is growing. The acceptors, in particular, offer opportunities that are complementary to donors due to their relatively large spin-orbit coupling [31][32][33], the absence of valleyorbit coupling [34][35][36][37], and suppressed hyperfine interaction [38,39].…”

“…For a sufficiently selective atomic resist, this will be confined to the initial depassivation window, leading to atomic-precision placement of the dopant i.e., within ± 1 lattice sites of the target [23]. This methodology has recently been extended to acceptor δ-doping layers of silicon using precursors of diborane (B 2 H 6 ), boron trichloride (BCl 3 ) and aluminum trichloride (AlCl 3 ) [27][28][29], but these techniques have not yet been demonstrated for a single acceptor. Furthermore, to reliably fabricate devices consisting of many precisely placed single acceptor atoms (e.g., the sites in an analog quantum simulator for the Fermi-Hubbard model) the probability of incorporation needs to be deterministic, i.e.…”

“…In this work, we develop several Kinetic Monte Carlo (KMC) models based on previously calculated first principles reaction pathways [29,64,65] to predict the singleacceptor incorporation statistics of three recently explored atomic-precision acceptor precursors [27][28][29]: diborane, boron trichloride, and aluminum trichloride in both monomer and dimer forms. We demonstrate that while single-acceptor atomic-precision incorporation is possible for all precursors, they are not equally likely to incorporate.…”

Multihole models for deterministically placed acceptor arrays in silicon

“…For linear chains of acceptors, an independent-hole model was developed, including the contribution of cubic terms, and the existence of nontrivial single-particle topological edge states was demonstrated for finite chains, and related to band invariants of the corresponding infinite systems [12]. These investigations of pairs and linear arrays of acceptors suggest that the emerging techniques of deterministic doping [13] could lead to interesting results if applied to acceptors [14]. Advances in the experimental characterization of acceptors in silicon include measurements of the optical transitions and spectra of acceptors [15], measurement of the coherence time of the excited state of acceptors [16], and a study of transport properties of boron-doped material [17], etc.…”