A method of forming infra red detector arrays is described, starting with the manufacture of a wafer. The wafer is formed from a GaAs or GaAs/Si substrate having CMT deposited thereon by MOVPE. The CMT deposited can include a number of layers of differing composition, the composition being controlled during the MOVPE process and being dependent on the thickness of the layer deposited. A CdTe buffer layer can aid deposition of the CMT on the substrate. Once the wafer is formed, the buffer layer, an etch stop layer and any intervening layers can be etched away leaving a wafer suitable for further processing into an infra red detector.
