Superconductivity in laser-annealed monocrystalline silicon films: The role of boron implant

Abstract

33 nm thick silicon on insulator films were implanted with boron at high dose (1.5 × 1016 or 2.5 × 1016 at/cm2) and low energy (3 or 4 keV), then further annealed with 160 ns laser pulses. When the laser energy is set such as to lead to the near complete melt of silicon, superconductivity is found in 4 keV-implanted films only, with a critical temperature that increases with dose from 270 to 390 mK. This latter temperature is 200 mK higher than the one recently reported in polycrystalline films of same thickness. Transmission electron microscopy images demonstrate that the films annealed at this particular laser energy are monocrystalline, with a lower density of boron precipitates in superconducting ones at a given dose. A simple model shows that the appearance of superconductivity in 4 keV-implanted films is due to the broader shape of the as-implanted boron distribution.