Gallium(II) sulfide, GaS, is a

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

gallium Gallium is a chemical element; it has Chemical symbol, symbol Ga and atomic number 31. Discovered by the French chemist Paul-Émile Lecoq de Boisbaudran in 1875, elemental gallium is a soft, silvery metal at standard temperature and pressure. ...

and

sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...

. The normal form of gallium(II) sulfide as made from the elements has a hexagonal layer structure containing Ga₂⁴⁺ units which have a Ga-Ga distance of 248pm. This layer structure is similar to

GaTe A gate or gateway is a point of entry to or from a space enclosed by walls. The word is derived from Proto-Germanic language, Proto-Germanic ''*gatan'', meaning an opening or passageway. Synonyms include yett (which comes from the same root w ...

, GaSe and InSe. An unusual metastable form, with a distorted wurtzite structure has been reported as being produced using MOCVD. The metal organic precursors were di-tert-butyl gallium dithiocarbamates, for example Ga^tBu₂(S₂CNMe₂) and this was deposited onto GaAs. The structure of the GaS produced in this way is presumably Ga²⁺ S²⁻. Single layers of gallium sulfide are dynamically stable two-dimensional semiconductors, in which the valence band has an inverted Mexican-hat shape, leading to a Lifshitz transition as the hole-doping is increased. Gallium(II) sulfide demonstrates nonlinear optical activities, including second-harmonic generation and two-photon excited fluorescence.

References

Monosulfides Gallium compounds {{inorganic-compound-stub