can't read?
Gallium arsenide (GaAs) is a compound of the elements gallium and arsenic.
Gallium arsenide (GaAs substrate), <100>, (undoped, 10 x 10 x 0.5 mm) - used as a substrate material for the epitaxial growth of other III-V semiconductors including: Indium gallium arsenide, Aluminium gallium arsenide and others.