||1.07 eV 
||Germanium (II) selenide, selanylidenegermanium
|Classification / Family
Transition metal mono-chalcogenides (TMMCs), 2D semiconductor materials, Nano-electronics, Nano-photonics, Photovoltaic, Materials science
||Synthetic - chemical vapour transport (CVT)
Germanium selenide (GeSe) has a puckered layer structure similar to that of black phosphorus. However, unlike BP, each germanium cation is triple-coordinated with a lone electron pair pointing to the inter-layer spacing. The lone electron pair thus is subject to inter-layer coupling to enhance the binding force between layers.
The high quality of TMDC monolayers have been mostly been fabricated by mechanical and chemical exfoliations from bulk crystals or high-purity powders. However, few-to-monolayer GeSe films with direct bandgaps are still hard to obtain by mechanical exfoliation due to the high fragility of GeSe mono-crystalline flakes. Liquid-phase exfoliation of high-purity powders is an alternative way to prepare GeSe nanosheets or nanoparticles.
Germanium selenide is a p-type semiconductor with closely-located direct and indirect band gaps in the range of 1.1 – 1.2 eV. GeSe also exhibits a high absorption coefficient of ~105 cm−1 in the visible range and a high hole mobility of 128.6 cm2 V−1 s−1, making it a promising semiconductor for electronic and opto-electronic applications (such as photovoltaics, phototransistors, thermoelectrics, and energy storage devices).
Germanium selenide powder is obtained via the CVT method, with a purity in excess of 99.995% achieved.
Germanium selenide powder is suitable for liquid chemical exfoliation to prepare GeSe nanosheets and nanoparticles down to few-layer films. GeSe powder is also used for preparation of mono-layer and few-layer films via chemical vapour deposition (CVD).
Literature and Reviews
Electronic structure of germanium selenide investigated using ultra-violet photoelectron spectroscopy, P Mishra et al., Semicond. Sci. Technol., 30, 075001 (2015); doi:10.1088/0268-1242/30/7/075001.
- GeSe monolayer semiconductor with tunable direct band gap and small carrier effective mass, Y. Hu et al., Appl. Phys. Lett. 107, 122107 (2015); doi: 10.1063/1.4931459.
Two-Dimensional GeSe as an Isostructural and Isoelectronic Analogue of Phosphorene: Sonication-Assisted Synthesis, Chemical Stability, and Optical Properties, Y. Ye et al., Chem. Mater., 29, 8361−8368 (2017); DOI: 10.1021/acs.chemmater.7b02784.
Anisotropic Spin Transport and Strong Visible-Light Absorbance in Few-Layer SnSe and GeSe, G. Shi et al., Nano Lett., 15, 6926−6931 (2015); DOI: 10.1021/acs.nanolett.5b02861.
Band Structure and Photoelectric Characterization of GeSe Monolayers, Adv. Funct. Mater., 28, 1704855 (2018); DOI: 10.1002/adfm.201704855.
Highly Anisotropic GeSe Nanosheets for Phototransistors with Ultrahigh Photoresponsivity, X. Zhou et al., Adv. Sci., 5, 1800478 (2018); DOI: 10.1002/advs.201800478.