Applications requiring large-area semiconductor coverage rely increasingly on amorphous and heterogeneous silicon materials because they can be deposited at low cost on a variety of substrates. This volume, first published in 1999, covers the range from fundamental research to the device applications of these materials. A special session on medium-range order is featured, and confirms the belief that ordering correlates with the electronic quality of a-Si: H films. Important experimental observations on metastable effects in a-Si: H are also reported, as are devices and processing strategies. Topics include: growth and properties; high-rate deposition; recrystallization, amorphization and porous silicon; ordering and hydrogen; metastability; defects, band tails and transport; heterogeneous materials and devices; thin-film transistors and displays; solar cells; and detectors, imagers and other device