Number 73 (Story #1), March 27, 1992 by Phillip F. Schewe and Ben Stein|
THE CAPACITANCE OF SINGLE QUANTUM DOTS has been measured with a resolution of 1 attofarad (10-18 F). Quantum dots are tiny islands of semiconductors (less than 1 micron on a side) in which confinement in all three spatial dimensions gives rise to interesting quantum effects. Normally, because of their small size and because of the way in which they are made, the dots are usually studied many at a time. But at last week's APS March Meeting in Indianapolis, Raymond Ashoori of AT&T Bell Labs (908-582-7350) described how to study just one. Starting with a 2-dimensional electron gas in a thin layer of gallium arsenide between layers of aluminum gallium arsenide, Ashoori further restricts the movement of electrons in the two lateral directions by applying voltage potentials, which pinch off forbidden areas. The charge in the dot can be monitored to less than a fraction of a single electron charge, permitting a high-resolution capacitance measurement.