Thin epitaxial films have been grown on (100) semi‐insulating (SI ) by close‐spaced vapor transport (CSVT). The epitaxy has been confirmed by x‐ray diffraction spectra and SEM observation of etch pit shapes and orientations. The effect of hydrogen flux, water vapor pressure, distance between the source and the substrate, and transport temperature on the film growth has been measured and analyzed. A model based on the variation of the equilibrium constants of the reactions occurring at the surface of the source and the substrate has been developed to elucidate the growth of. The measurements of transport properties, performed on the CSVT depositions, show that the deposited films are always n‐type independently of the used source (n‐type, p‐type, or SI ). The unintentionally introduced dopant concentration may vary from . It is shown that shallow traps associated to EL2 deep levels can be responsible for part of this doping, on the lowest charge carrier density side, but not above . An unwanted dopant is always introduced by the present technique. It is proposed that Si could be the unwanted doping agent.