Number 169 (Story #4), March 17, 1994 by Phillip F. Schewe and Ben Stein GERMANIUM-SILICON TRANSISTORS are more than twice as fast as silicon transistors and this year IBM, in collaboration with the company Analog Devices, will market GeSi products, such as analog-to-digital converters. Until recently it had been difficult to make integrated circuits with germanium because of the 4% lattice mismatch between germanium and silicon; this resulted in a disruptive strain in the interfaces present in all semiconductor devices. This problem was solved by using not pure Ge on silicon but a GeSi alloy. Still, the use of GeSi in commercial products was delayed because the fabrication process---whether molecular beam epitaxy or high-temperature chemical vapor deposition (CVD)---was so arduous. More recently IBM researchers have devised a lower-temperature CVD process and circuits can now be manufactured economically. GeSi devices have operated at switching speeds as great as 117 GHz. (Scientific American, Jan. and Mar. 1994; Physics World, Feb. 1994.)