Magnesium selenide

Magnesium selenide is an inorganic compound with the chemical formula MgSe. It contains magnesium and selenium in a 1:1 ratio. It belongs to the II-VI family of semiconductor compounds.

Structure
Three crystal structures for MgSe have been experimentally characterized. The rock-salt structure is considered to be the most stable crystal structure that has been observed in bulk samples of MgSe, and a cubic lattice constant of 0.55 nm was deduced for this structure. Although attempts at preparing pure zincblende MgSe have been unsuccessful, the lattice constant of zincblende MgSe has been extrapolated from epitaxial thin films of zincblende MgxZn1-xSySe1-x and MgxZn1-xSe grown on gallium arsenide, the latter of which was prepared with a high magnesium content (up to 95% Mg, i.e., Mg0.95Zn0.05Se). There is good agreement between these and other extrapolations that the lattice constant of pure zincblende MgSe is 0.59 nm. The wurtzite structure of MgSe has been observed, but it is unstable and slowly converts to the rock-salt structure.

NiAs- and FeSi-type crystal structures of MgSe are predicted to form by subjecting the rock-salt crystal structure to extremely high pressures.

Electronic properties
Both rock-salt and zincblende MgSe are semiconductors. On the basis of different extrapolations, a room temperature bandgap of 4.0 eV has been recommended for zincblende MgSe. A room temperature bandgap of 3.9 eV was determined for rock-salt MgSe.

Preparation
Thin films of amorphous, wurtzite and rock-salt MgSe have been prepared by vacuum deposition of Mg and Se at cryogenic temperatures, followed by heating and annealing. Compound semiconductor alloys of MgSe, such as MgxZn1-xSe, have been prepared by molecular beam epitaxy.

Reactions
Samples of pure MgSe and Mg-rich MgxZn1-xSe (x > 0.7) readily react with water and oxidize in air.