The results of controlled doping of CdxHg1-xTe epitaxial layers are presented. The investigated layers were obtained by the evaporation-condensation-diffusion method in the process of isothermal growth. The process of auto diffusion from the solid phase was investigated. This process consists in the diffusion of As dopants from CdTe substrate into the grown epitaxial layer. Two types of CdTe substrates, uniformly doped in the process of synthesis and unalloyed with ion implanted surface layer, have been used as sources of As diffusant. Comparative analysis of galvanomagnetic measurements and SIMS spectra was carried out. The results of investigations indicate the very high, almost 100%, electrical activity of As dopants in the CdxHg1-xTe epitaxial grown layer.