We report As doped HgCdTe materials grown by molecular beam epitaxy on Si substrate. The HgCdTe materials is doped in situ during growth with high structural quality using As crackers, realizing As doping concentration of 8×1018 cm-3. We have noticed that As doping is highly sensitive to parameters used in material growth such as growth temperature, As beam current, and material composition. By improving the manipulation of growth temperature and heating method of substrate, the distribution of As concentration in both the horizontal and vertical directions in the material can be more evenly distributed. Two-step annealing method is used for As activation. It is found that when the annealing temperature increases, the activation concentration increases as well, and the carrier mobility decreases significantly. When the concentration is below 3×1017 cm-3, the activation rate is close to 100%. With the As doping concentration increasing, the activation rate decreases.