Title: Transport and Tunneling in Atomic-Scale, Ultradoped Si:B Devices
Abstract: Hole spins in Si are a promising qubit platform that possesses long spin coherence times in 28Si and long-distance manipulation due to its intrinsic strong spin-orbit couplings. Recent work has exemplified the use of hole spins bound with acceptor atoms in Si as qubits. However, engineering an integrated hole spin qubits system requires atomic-precision advanced manufacturing (APAM) techniques to locate acceptors in a specific location without any defects. It mandates the proper precursors and the right atomic resists to achieve a mission to realize a hole spin qubit platform in Si. Halogen-based chemistries offer a promising path for making atomic-scale devices based on acceptors. In this work, we have demonstrated the formation of ultra B-doped δ-layer in Si via BCl3 and atomistic silicon-boron (Si:B) devices using APAM techniques. According to the secondary ion mass spectrometry (SIMS) depth profiling, we achieved ultradoping of Si:B: a peak of B concentration exceeded 1.0 × 1021 cm-3 and the areal dose was greater than 1.0 × 1014 cm-2. Thus, selectivity of BCl3 with H and Cl atomic resists was investigated through SIMS study and showed compatibility of BCl3 with the resists. At last, nanowires and single hole transistors (SHTs) were fabricated, and their electrical properties are characterized at low temperatures of 2.8 - 3.0 K. I-V relations of nanowires were linear, which indicates ohmic conduction. We observed the Coulomb blockade and calculated the barrier height of 50 ± 30 meV using Wentzel-Kramers-Brillouin (WKB) approximation. This study is indispensable research in realizing spin hole qubits in Si.