Behavior of surface hydrogen on a-Ge:H

The surface hydrogen on the growing surfaces of a-Ge:H films is studied by infrared reflection absorption spectroscopy to identify the behavior at different growth temperatures. Similar to the Si-counterparts, the dominant bonding configuration of surface Ge-H-x species shifts from x = 3 --> 2 --> 1 with increasing temperature. However, hydrogen desorption from the a-Ge:H surface is more gradual with a relatively low onset (about 110 degrees C) indicating that the desorption activation energy is smaller compared to that of a-Si:H surfaces. Post-growth studies have revealed that hydrogen dilution in the glow-discharge preparation of a-Ge:H is effective in stabilizing the surface Ge-H-x species against thermal desorption.