Abstract: Epitaxial layers of single crystals of gallium arsenide and similar compounds are formed by vapor deposition. A carrier gas flow is passed through a liquid halide of a group VB material to obtain a first vapor having a halogen, carrier gas and group VB material. The carrier gas flow is monitored and adjusted to obtain a predetermined mass of halogen and second material in this raw vapor. A final reactor input vapor is obtained with constant concentration and constant flow going into a reactor by monitoring the total volume of carrier gas in the raw vapor as added per unit of time and adjusting the raw vapor by adding a volume of additional carrier gas to a predetermined value to form a final reactor input vapor. The reaction and deposition of the epitaxial layer is then carried out in a reactor.