Phase-Specific Vapor–Liquid–Solid Growth of GeSe and GeSe₂ van der Waals Nanoribbons and Formation of GeSe–GeSe₂ Heterostructures

Abstract

Group IV (Ge, Sn) chalcogenides differ from most other two-dimensional (2D)/layered semiconductors in their ability to crystallize both as stable mono- and dichalcogenides. The associated diversity in structure and properties presents the challenge of identifying conditions for the selective growth of the different crystalline phases, as well as opportunities for phase conversion and materials integration/interface formation in heterostructures. Here, we discuss the phase-selective synthesis of free-standing GeSe and GeSe2 nanoribbons in a vapor–liquid–solid growth process over Au catalyst nanoparticles. Electron microscopy shows that the two types of ribbons adopt high-quality van der Waals structures with layering in the ribbon plane and with the ribbon axis aligned with the b-axis of GeSe and GeSe2, respectively. Nonspecific growth gives rise to a tapered morphology and, in the case of GeSe2, leads to nucleation of misoriented crystallites on the ribbon surface. The partial transformation of GeSe ribbons by selenization, finally reacts the outermost layers and edges to GeSe2, thus producing GeSe–GeSe2 core–shell heterostructures. Cathodoluminescence spectroscopy of as-grown GeSe ribbons and of GeSe–GeSe2 hybrids shows a marked enhancement of the luminescence intensity due to surface passivation by wide-band gap GeSe2 (E g = 2.5 eV). Our results support applications of germanium mono- and dichalcogenides as well as their heterostructures in areas such as optoelectronics and photovoltaics.

Germanium Selenide: A Critical Review on Recent Advances in Material Development for Photovoltaic and Photoelectrochemical Water‐Splitting Applications

“…GeSe-based TFSCs devices could experience adverse effects on their performance if GeSe 2 is formed in GeSe absorbing layer because GeSe 2 is a p-type semiconductor with a relatively wide E g of %2.7 eV. In an interesting study, Yumigeta et al [61] synthesized the nanostructures including GeSe and GeSe 2 via CVD method using halide-based precursors at atmospheric pressure and 400 °C temperature. By analyzing various physicochemical properties combined with a thorough analysis of CVD experiments, authors have concluded that the resulting stoichiometry and phase of GeSe and GeSe 2 nanosized materials are determined by several factors, including substrate temperature, selenium partial pressure, and the type of substrates used.…”

Optimized Substrate Orientations for Highly Uniform Metal Halide Perovskite Film Deposition

“…25,26 This approach inherently increases production cost due to the necessity of maintaining high-vacuum background and often suffers from a slow growth rate, 27 with growth variables closely tied to specific system geometries. In contrast, the tube furnace system offers versatility for the cost-effective growth of lowdimensional crystalline materials, such as 1D nanowires, 28,29 2D materials, 30,31 and thin films. 32,33 With its capacity for high quality and yield, 23 the tube furnace stands out as a more suitable option for potential scale-up processes, such as continuous roll-to-roll processing on a large-area substrate.…”

“…This is because the morphology of MHP crystals, including attributes such as grain size and film thickness, fundamentally dictates their carrier generation and transport properties, and hence, their overall optoelectronic performance. ,, While prior reports on vapor deposition of MHPs have emphasized their potential for large-area film growth, , the majority employ direct source evaporation onto a substrate in a vacuum chamber. , This approach inherently increases production cost due to the necessity of maintaining high-vacuum background and often suffers from a slow growth rate, with growth variables closely tied to specific system geometries. In contrast, the tube furnace system offers versatility for the cost-effective growth of low-dimensional crystalline materials, such as 1D nanowires, , 2D materials, , and thin films. , With its capacity for high quality and yield, the tube furnace stands out as a more suitable option for potential scale-up processes, such as continuous roll-to-roll processing on a large-area substrate . Despite this, ensuring spatially uniform films in such a system is challenging due to the uncontrollable precursor concentration and spatially nonuniform growth kinetics.…”