In this paper the influence of low-energy Ar ion beam milling (IBM) on the properties of n- type Hg<sub>1-x</sub>Cd<sub>x</sub>Te crystals has been studied. The as growth samples as well as these with thin Au layers deposited on the surface before irradiation has been investigated. The milling was carried out at room temperature and ions energy was 2 keV. In the initial samples the electronic properties of the near surface layer of 50 mm thick were changed. From Petritz model of the Hall results of two layer system the mobility and concentration of charge carriers in the modified layers were determined. In the samples with metal layer the doping caused by IBM is observed. In the case of Au the compensation phenomena is addressed. The model of defects created and theirs diffusion is discussed.