Method of making a high band-gap opto-electronic device

A method of providing an electro-optical device, comprising the steps of:

• providing a first substrate layer formed of gallium arsenide;
• growing a second graded layer composed of aluminum gallium indium phosphide which is one of adjacent to and on top of said first substrate layer by periodically substituting aluminum atoms for gallium atoms of said gallium arsenide so as to maintain lattice matching between said first substrate layer and said second graded layer;
• and
• growing an active section composed of aluminum gallium indium phosphide on said second graded layer so as to form a boundary therewith, said active section being substantially lattice matched with said first substrate layer and said second graded layer and having higher energy band gaps than said first substrate layer,
• whereby said second graded layer has a varying energy band gap such that an energy band gap of said second graded layer at said boundary substantially equals that of the active section of the boundary and decreases to a lesser energy band gap away from said boundary.