High-pressure melt growth and transport properties of SiP, SiAs, GeP, and GeAs 2D layered semiconductors

TL;DR

This study reports the successful high-pressure melt growth of bulk single crystals of SiP, SiAs, GeP, and GeAs, revealing their layered structures, semiconducting properties, and potential for 2D device applications.

Contribution

It introduces a novel high-pressure melt-growth method for these layered semiconductors and demonstrates their structural and electrical properties.

Findings

Crystals of GeP, GeAs, and SiAs were large and exfoliable.

All compounds are layered and stable at low temperatures.

GeP, GeAs, and SiAs exhibit 2D-Variable Range Hopping conduction.

Abstract

Silicon and Germanium monopnictides SiP, SiAs, GeP and GeAs form a family of 2D layered semiconductors. We have succeeded in growing bulk single crystals of these compounds by melt-growth under high pressure (0.5-1 GPa) in a cubic anvil hot press. Large (mm-size), shiny, micaceous crystals of GeP, GeAs and SiAs were obtained, and could be exfoliated into 2D flakes. Small and brittle crystals of SiP were yielded by this method. High-pressure sintered polycrystalline SiP and GeAs have also been successfully used as a precursor in the Chemical Vapor Transport growth of these crystals in the presence of I$_{2}$ as a transport agent. All compounds are found to crystallize in the expected layered structure and do not undergo any structural transition at low temperature, as shown by Raman spectroscopy down to T=5K. All materials exhibit a semiconducting behavior. The electrical resistivity of GeP, GeAs and SiAs is found to depend on temperature following a 2D-Variable Range Hopping conduction mechanism. The availability of bulk crystals of these compounds opens new perspectives in the field of 2D semiconducting materials for device applications.