Structural properties of TaAs Weyl semimetal thin films grown by molecular beam epitaxy on GaAs(001) substrates

TL;DR

This study reports the growth and structural analysis of TaAs Weyl semimetal thin films on GaAs(001) substrates, revealing their crystalline quality, defect structure, and relaxation behavior using various microscopy and diffraction techniques.

Contribution

It demonstrates the successful epitaxial growth of TaAs thin films on GaAs(001) with detailed structural characterization, despite significant lattice mismatch.

Findings

No misfit dislocations observed at the interface.

TaAs layers are fully relaxed at initial deposition.

Columnar structure with uniform orientation and crystalline quality.

Abstract

Thin crystalline layers of TaAs Weyl semimetal (9 and 18 nm thick) are grown by molecular beam epitaxy on GaAs(001) substrates. The (001) planes of the tetragonal TaAs lattice are parallel to the GaAs(001) substrate, but the corresponding in-plane crystallographic directions of the substrate and the layer are rotated by 45{\deg}. In spite of a substantial lattice mismatch (about 19%) between GaAs(001) substrate and TaAs epilayer no misfit dislocations are observed at the GaAs(001)/TaAs(001) interface. Only stacking fault defects in TaAs are detected with transmission electron microscopy. Thorough X-ray diffraction measurements and analysis of the in-situ reflection high energy electron diffraction images indicates that TaAs layers are fully relaxed already at the initial deposition stage. Atomic force microscopy imaging reveals the columnar structure of the layers, with lateral (parallel to the layer surface) columns about 20 nm wide and 200 nm long. Both X-ray diffraction and transmission electron microscopy measurements indicate that the columns share the same orientation and crystalline structure.