Atomic layer deposition and superconducting properties of NbSi films

TL;DR

This study demonstrates the synthesis of stoichiometric NbSi films via atomic layer deposition, revealing their structural, electronic, and superconducting properties, including a superconducting transition at 3.1K, a novel achievement for this material.

Contribution

First successful growth of stoichiometric NbSi films with superconducting properties using atomic layer deposition, providing new insights into their synthesis and characteristics.

Findings

Films are amorphous with a density of 6.65 g/cm³.

Superconducting transition observed at Tc=3.1K.

Growth rate remains constant between 150-275°C, increases above 300°C.

Abstract

Atomic layer deposition was used to synthesize niobium silicide (NbSi) films with a 1:1 stoichiometry, using NbF5 and Si2H6 as precursors. The growth mechanism at 200oC was examined by in-situ quartz crystal microbalance (QCM) and quadrupole mass spectrometer (QMS). This study revealed a self-limiting reaction with a growth rate of 4.5 {\AA}/cycle. NbSi was found to grow only on oxide-free films prepared using halogenated precursors. The electronic properties, growth rate, chemical composition, and structure of the films were studied over the deposition temperature range 150-400oC. For all temperatures, the films are found to be stoichiometric NbSi (1:1) with no detectable fluorine impurities, amorphous with a density of 6.65g/cm3, and metallic with a resistivity {\rho}=150 {\mu}{\Omega}.cm at 300K for films thicker than 35 nm. The growth rate was nearly constant for deposition temperatures between 150-275oC, but increases above 300oC suggesting the onset of non-self limiting growth. The electronic properties of the films were measured down to 1.2K and revealed a superconducting transition at Tc=3.1K. To our knowledge, a superconducting niobium silicide film with a 1:1 stoichiometry has never been grown before by any technique.