The present invention relates to a substrate (5) comprising a Si-base (1) and an InAs-layer (4) provided on said Si-base where said InAs-layer (4) has a thickness between 100 and 500 nanometers and root-mean-square roughness of the upper surface of said InAs-layer (4) is below 1 nanometer. The invention further relates to a method for forming said substrate. The invention also relates to growing InAs-nanowires (7) as well as a GaSb-layer (17) on said substrate (5).
