In the industrialized world, we are seldom more than a few meters from a crystal of silicon. One crystal may be strapped to our wrist, in an electronic watch; others may be buried within a nearby calculator, video recorder or auto ignition system—indeed, one may even be lurking in the quartz movement of a new “antique” clock. These crystals are extraordinarily perfect: No more than than one atom in is out of a proper lattice site, and the total impurity concentration may be less than 0.1 parts per billion. Yet a microprocessor or a megabit memory can be fabricated in a crystal of silicon costing only 15–20 cents
Epitaxial growth of germanium‐silicon alloys or metal silicides on silicon produces structures that can be used in high‐performance optical and electronic devices.