2D SnS: a phosphorene analogue with strong in-plane electronic anisotropy

TL;DR

This study investigates the anisotropic electronic properties of 2D SnS, demonstrating strong in-plane conductivity differences and identifying defect-induced p-type doping, with potential implications for anisotropic electronic devices.

Contribution

The paper provides experimental characterization of 2D SnS's anisotropic electronic properties, confirming theoretical predictions and linking defect levels to p-type conductivity.

Findings

Zigzag and armchair directions identified via microscopy and spectroscopy.

Mobility along zigzag exceeds 20 cm²V⁻¹s⁻¹, 1.7 times higher than in armchair.

Sn deficiency causes p-type conductivity with a defect level around 42-45 meV.

Abstract

We study the anisotropic electronic properties of 2D SnS, an analogue of phosphorene, grown by physical vapor transport. With transmission electron microscope and polarized Raman spectroscopy, we identify the zigzag and armchair directions of the as-grown 2D crystals. 2D SnS field-effect transistors with a cross-Hall-bar structure are fabricated. They show heavily hole-doped (~10$^{19}$ cm$^{-3}$) conductivity with strong in-plane anisotropy. At room temperature the mobility along the zigzag direction exceeds 20 cm$^{2}$V$^{-1}$s$^{-1}$, which can be up to 1.7 times of that in the armchair direction. This strong anisotropy is then explained by the effective-mass ratio along the two directions and agrees well with previous theoretical predictions. Temperature-dependent carrier density is used to find out the acceptor energy level to be ~45 meV above the valence band maximum. This value matches with a calculated defect level of 42 meV for Sn vacancies, indicating that Sn deficiency is the main cause of the p-type conductivity.