Comprehensive Research on Stability of Amorphous Silicon and Alloy Materials and Devices: Annual Report, 31 May 1995 - 30 May 1996

This report represents the progress achieved during the second year of Iowa State University's program to develop a-Si:H and a-SiGe:H materials and devices with better stability by changing the chemistry of the growth technique. Researchers shifted their ephasis from cells made on tin oxide substrates (superstrate cells) to cells made on stainless-steel substrates (substrate cells). By inducingion bombardment and etching using both H-ECR (electron-cyclotron-resonance) and He-ECR discharges, researchers can induce a more perfect lattice structure and thereby improve the properties of the films and devices. Researchers found that He-beam-produced films have a lower H content and a smaller Tauc bandgap than films produced using a H-beam-discharge. The stability of the H-beam-producedfilms is much better than that of the He-beam-produced films, even though the He-produced films had a lower H content. From the results of the stability studies of both films and devices, resesarchers conclude that it is not the H content in the film that primarily affects stability, but rather, the influence of H on the growth chemistry. In particular, having an etching-type growth chemistryfor both films and devices seems to be beneficial for improving stability without sacrificing electronic properties.