[Paper Review] Molecular Beam Epitaxy Growth of Wafer-scale SnSe van der Waals Ultrathin Layers

Qihua Zhang, Maria Hilse+3 more|arXiv (Cornell University)|Feb 26, 2026

2D Materials and Applications0 citations

TL;DR

The paper demonstrates wafer-scale growth of ultrathin SnSe layers via molecular beam epitaxy, identifying a growth window and a three-step process to achieve uniform, high-quality films down to 5 nm.

ABSTRACT

Tin selenide (SnSe) is a van der Waals (vdW) layered post-transition metal monochalcogenide compound which is promising for a wide range of device applications when its thickness is reduced to a few layers. Hence, developing a mature synthesis technique to obtain wafer-scale, high-quality ultrathin SnSe layers is crucial. In this work, we present a comprehensive study on the effect of growth parameters on the material quality of ultrathin SnSe thin films grown by molecular beam epitaxy. A growth window including substrate temperature of 210-270°C and low Se/Sn flux ratio with Se valve position of 10-30 mils has been identified which results in SnSe films with root-mean-square (RMS) roughness as low as 0.6 nm and full-width-at-half-maximum (FWHM) of 0.1° in SnSe (400) x-ray diffraction (XRD) rocking curve. Finally, using a three-step growth approach, we demonstrate wafer-scale coalesced ultrathin SnSe layers with thicknesses from 20 nm down to 5 nm, with good crystallinity, structural quality, and surface morphology. This work establishes a growth condition framework for MBE-grown SnSe and presents a viable route for developing wafer-scale single-layer films, unlocking the potential of this highly promising material for advanced device integration.

Motivation & Objective

• Motivate development of mature synthesis techniques for wafer-scale, high-quality ultrathin SnSe layers.
• Systematically study how growth parameters affect SnSe thin-film quality.
• Establish a growth window and a reproducible three-step growth method for uniform ultrathin SnSe films.

Proposed method

• Use molecular beam epitaxy to grow SnSe on suitable substrates.
• Explore growth parameter space including substrate temperature (210–270°C) and Se/Sn flux ratio.
• Vary Se valve position between 10–30 mils to optimize stoichiometry and surface quality.
• Characterize films via RMS roughness and XRD (FWHM of SnSe (400) rocking curve).
• Develop a three-step growth procedure to achieve wafer-scale coalesced ultrathin SnSe layers from 20 nm to 5 nm.

Experimental results

Research questions

• RQ1 What growth conditions yield the lowest surface roughness and best crystallinity for SnSe ultrathin layers?
• RQ2 Can wafer-scale, coalesced SnSe ultrathin films be produced reliably from 20 nm down to 5 nm thicknesses?
• RQ3 What is the relationship between substrate temperature, Se/Sn flux, and film quality in MBE-grown SnSe?

Key findings

• A growth window of 210–270°C and low Se/Sn flux with Se valve 10–30 mils yields RMS roughness as low as 0.6 nm.
• XRD rocking curve FWHM of 0.1° for SnSe (400) indicates good crystalline quality.
• A three-step growth approach produces wafer-scale coalesced ultrathin SnSe layers from 20 nm down to 5 nm with good crystallinity and surface morphology.