The present invention relates generally to methods and apparatus for the controlled growing of material on substrates. According to embodiments of the present invention, a precursor feed is controlled in order to provide an optimal pulse profile. This may be accomplished by splitting the feed into two paths. One of the paths is restricted in a continuous manner. The other path is restricted in a periodic manner. The output of the two paths converges at a point prior to entry of the reactor. Therefore, a single precursor source is able to fed precursor in to a reactor under two different conditions, one which can be seen as mimicking ALD conditions and one which can be seen as mimicking CVD conditions. This allows for an otherwise single mode reactor to be operated in a plurality of modes including one or more ALD/CVD combination modes. Additionally, the pulse profile of each pulse can be modified. The pulse profile can be modified to create a low or very low partial pressure pulse profile at the beginning of a pulse.