Abstract

A new generation of microelectronic devices will be based on ballistic and quantum tunneling transport processes, which involve transit times on a femtosecond scale across submicron semiconductor layers. Fundamental experimental studies of these phenomena will require the use of femtosecond optical techniques to inject and probe carriers locally, just as analogous picosecond techniques have been used in studying slower transport processes in thicker layers^1,2. However, because optical absorption (and therefore carrier injection) depths at near band gap wavelengths (typically 1μm.) greatly exceed the thickness of the semiconductor layers in which most femtosecond transport phenomena occur (typically .01 to 0.1 μm.), adequate spatial resolution to observe these processes directly has not been achievable. We introduce a new technique for optically injecting carriers of any desired energy within the first few hundred angstroms of the surface of a semiconductor layer with femtosecond time resolution, so that the evolution of femtosecond transport processes can be resolved.

© 1987 Optical Society of America