Effect of near-substrate plasma density in the reactive magnetron sputter deposition of hydrogenated amorphous germanium

The properties of hydrogenated amorphous germanium (a-Ge:H) are studied as a function of near-substrate plasma density and hydrogen partial pressure at fixed temperature. Near substrate plasma density is varied by using an unbalanced magnetron and an external magnetic field, and characterized using a guard ring flat probe and a cylindrical Langmuir probe. Films are characterized by infrared absorption, optical transmission, dark conductivity, activation energy, and photoconductivity. A major effect of increasing the near-substrate plasma density is to increase the dihydride component content of the films. The photoconductivity of these films is lower than those whose hydrogen content is increased by increasing the hydrogen partial pressure during deposition, implying a degradation in film properties with increasing near-substrate plasma density. These results show that chemical effects, as well as ion bombardment effects, need to be considered in the plasma-based deposition of a-Ge:H.