Indium(II) selenide

Indium(II) selenide (InSe) is an inorganic compound composed of indium and selenium. It is a III-VI layered semiconductor. The solid has a structure consisting of two-dimensional layers bonded together only by van der Waals forces. Each layer has the atoms in the order Se-In-In-Se.^[2]

Indium(II) selenide

Identifiers
CAS Number	1312-42-1
3D model (JSmol)	Interactive image
ChemSpider	4906850
PubChem CID	101946410
InChI InChI=1S/In.Se Key: NMHFBDQVKIZULJ-UHFFFAOYSA-N
SMILES [Se].[In]
Properties
Chemical formula	InSe
Molar mass	193.789 g·mol−1
Density	5.0
Melting point	611 °C (1,132 °F; 884 K)[1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Potential applications are for field effect transistors, optoelectronics, photovoltaic, non-linear optics, strain gauges,^[2] and methanol gas sensors.^[3]

Formation

Indium(II) selenide can be formed via a number of different methods. A method to make the bulk solid is the Bridgman/Stockbarger method, in which the elements indium and selenium are heated to over 900 °C in a sealed capsule, and then slowly cooled over about a month.^[4] Another method is electrodeposition from a water solution of indium(I) sulfate and selenium dioxide.^[5]

Properties

Diagram of polytopes of indium(II) selenide^[4]

There are three polytopes or crystal forms. β, ε are hexagonal with unit cells spanning two layers. γ has rhombohedral crystal system, with the unit cell including four layers.^[2]

β-Indium(II) selenide can be exfoliated into two-dimensional sheets using sticky tape. In a vacuum these form smooth layers. However, when exposed to air, the layers become corrugated because of chemisorption of air molecules.^[6] Exfoliation can also take place in isopropanol liquid.^[7]

Indium (II) selenide is stable in ambient conditions of oxygen and water vapour, unlike many other semiconductors.^[2]

polytope	space group	unit cell	band gap	eV
β	P63/mmc	a=4.005 c=16.660 Z=4	direct	1.28
γ	R3m	a=7.1286 Å, c=19.382 Å and Z=6	direct	1.29
ε	P6m2		indirect	1.4

Doping

The properties of indium(II) selenide can be varied by way of altering the exact ratio of elements from 1:1, creating vacancies. It is hard to get an exact equality. The properties can be compensated by transition element doping. Other elements that can be included in small concentrations are boron,^[8] silver,^[9] and cadmium.^[10]