“…21, indicating an exponential increase, by roughly a factor of 300 overall, as x varies from 0 to 1. [29,38,39] Figures 20 and 21 indicate that the 3 series of a-Si,Ge:H samples that my group has investigated (from U. Delaware, Harvard, and Uni-Solar) come very close to being optimized in the sense that they exhibit Urbach tail energies as low as high quality a-Si:H and also quite low deep defect levels overall. One additional indicator that these a-Si,Ge:H alloy samples are optimized is the degree to which they obey the spontaneous bond breaking model of M.…”