deposition zone and idle and annealing operations in the dwell zone in a sense independently the geometry of the reactor and adjusted flow rates of gases make the flow pattern in the deposition zone laminar which is favorable for the fine controlled and manageable pretreatment and growth process the length of the reactor and uniformity in temperature distribution are sufficient enough to operate with 3 4 substrates at a time the effect of the pretreatment method using gas products of the reaction between aluminum and hydrogen chloride is verified by the exemplary pretreatment of sapphire substrates for the hvpe gan growth embodiment 1 and by the exemplary pretreatment of sic substrates for the hvpe aln growth embodiment 2 the pretreatment method of this invention is described herein using the following exemplary embodiments a 0001 sapphire u03b1 al 2 o 3 substrate is used for the pretreatment and subsequent epitaxial deposition of the gallium nitride gan layer by hydride vapor phase epitaxial hvpe technique according to the present invention pretreatment of the sapphire substrate is performed using gas products of the reaction between aluminum al and hydrogen chloride hcl the reaction takes place in the source zone of the reactor where metallic al reacts with the gaseous hcl flowing over it the transport of the gas products to the deposition zone is assisted by argon ar as a carrier gas however carrier gases such as hydrogen h nitrogen n.