Semiconductor process technology and devices are provided, including a method for forming a high quality group III nitride layer on a silicon substrate and to a device obtainable therefrom. According to the method, a pre-dosing step is applied to a silicon substrate, wherein the substrate is exposed to at least 0.01 μmol/cm2 of one or more organometallic compounds containing Al, in a flow of less than 5 μmol/min. The preferred embodiments are equally related to the semiconductor structure obtained by the method, and to a device comprising said structure.