Abstract: The reactor includes: a chamber having a lower wall, an upper wall and a sidewall connecting the lower wall to the upper wall; a support plate mounted inside the chamber; at least one first supply line for a first gas, and at least one separate second supply line for a second gas; a gas injection device; and a gas collector. The gas injection device includes at least one injector connected to the first supply line and at least one injector connected to the second supply line, the injectors leading into the chamber through at least one inlet provided in the sidewall; all of the injectors of the first supply line and all of the injectors of the second supply line are connected one above the other; and the collector includes at least one outlet in the sidewall, opposite the inlet relative to the support plate, and substantially at the inlet.