Few-Layer to Multilayer Germanium(II) Sulfide: Synthesis, Structure, Stability, and Optoelectronics

Journal Article · Mon Jul 15 00:00:00 EDT 2019 · ACS Nano

DOI:https://doi.org/10.1021/acsnano.9b03986· OSTI ID:1573814

Sutter, Eli  ^[1]; Zhang, Bo  ^[1]; Sun, Muhua ^[1]; Sutter, Peter  ^[2]

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1. Univ. of Nebraska-Lincoln, Lincoln, NE (United States). Dept. of Mechanical and Materials Engineering
2. Univ. of Nebraska-Lincoln, Lincoln, NE (United States). Dept. of Electrical and Computer Engineering

Among 2D/layered semiconductors, group IV monochalcogenides such as SnS(e) and GeS(e) have attracted attention as phosphorene/black phosphorus analogues with anisotropic structures and predicted unusual properties. In contrast to SnS, for which bottom-up synthesis has been reported, few-layer GeS has been realized primarily via exfoliation from bulk crystals. Here, we report the synthesis of large (up to >20 μm), faceted single crystalline GeS flakes with anisotropic properties using a vapor transport process. In situ electron microscopy is used to identify the thermal stability and sublimation pathways, and demonstrates that the GeS flakes are self-encapsulated in a thin, sulfur-rich amorphous GeS_x shell during growth. Here, the shell provides exceptional chemical stability to the layered GeS core. In contrast to exfoliated GeS, which rapidly degrades during exposure to air, the synthesized GeS–GeS_x core–shell structures show no signs of chemical attack and remain unchanged in air for extended time periods. Measurements of the optoelectronic properties by photoluminescence spectroscopy show a tunable bandgap due to out-of-plane quantum confinement in flakes with thickness below 100 nm. Cathodoluminescence (CL) spectroscopy with nanoscale excitation provides evidence for interfacial charge transfer due to a type II heterojunction between the crystalline core and amorphous shell. Measurements by locally excited CL yield a minority carrier (electron) diffusion length in the p-type GeS core l^diff = 0.27 μm, on par with diffusion lengths in the highest-quality layered chalcogenide semiconductors.

• Research Organization: Univ. of Nebraska, Lincoln, NE (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Materials Sciences & Engineering Division
• Grant/Contract Number: SC0016343
• OSTI ID: 1573814
• Journal Information: ACS Nano, Vol. 13, Issue 8; ISSN 1936-0851
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
GeS flakes
in situ transmission electron microscopy
cathodoluminescence
optoelectronic properties
passivation