The invention relates to a device (1) and method for applying a carbon layer, in particular a diamond layer, to a substrate (2, 2a) by means of chemical vapour deposition, comprising a deposition chamber (3) into which a process gas, in particular molecular hydrogen and/or a mixture of molecular hydrogen and a carbon-containing gas, such as methane can be supplied, wherein a gas inlet and gas activation element (7) is provided in the form of a hollow body with a flow channel (7b) for the process gas, a wall (7a) surrounding the flow channel (7b), and an outlet opening (16) feeding from the flow channel (7b) into the deposition chamber (3), and a heating device (8) is provided for heating the wall (7a) of the gas inlet and gas activation element (7).