Properties of Hydrogenated Amorphous Silicon-Germanium Alloys Deposited by Dual Target Reactive Magnetron Sputtering

Hydrogenated amorphous silicon-germanium alloy thin films (a-Si1-xGex:H) were deposited using reactive magnetron sputtering. Dual targets of silicon and germanium were sputtered in an argon + hydrogen atmosphere using RF excitation. Films with x = 0.4 were deposited as a function of substrate temperature and hydrogen partial pressure, and were evaluated by dark and photoconductivity, infrared absorption, and optical transmission. Photosensitivity reached a maximum value of about 4500 between 150 and 200°C. Using the stretching modes in the region of 2000 cm-1, the hydrogen bonding was characterized in terms of the preferential attachment ratio (PA), which represents the ratio between H bonded to Si and H bonded to Ge. The PA shows a systematic increase with increasing temperature, generally independent of hydrogen partial pressure. The interplay between thermodynamic and kinetics effects in determining PA and film quality is discussed