Multijunction devices are an effective way to increase the efficiency of solar cell. However, currently only expensive III-V technologies utilize the infrared part of the solar spectrum. To tackle this issue, this work explores the material properties of thin film amorphous hydrogenated germanium deposited by PECVD. It was found that high H₂ dilution rates, deposition temperatures of 275 °C, pressures of 3 to 4 mbar and a power density around 0.20 W/m² can achieve films with bandgaps of around 0.9 eV and activation energies above 450 meV, suggesting dense films with intrinsic behaviour. Regarding the mechanisms governing this behaviour, the results suggest that the performance of a-Ge:H is predominantly determined by mid-gap states, which are related to the high mobility of H during deposition within the a-Ge:H matrix. When small amounts of Si are introduced, the H atoms are fixed to the Si, reducing the defect density in the material.