9408155 Fonstad Recent NSF-funded research at MIT has shown that InGaA1As quantum- well, tunnel-barrier heterostructures can be produced with intersubband energy level separations (n = 1 to n = 2) as large as 0.8 eV (1.55 um) and with TE-, as well as TM-, optical activity. The proposed research project builds on these results, and will focus (1) on developing structures with even larger level separations; (2) on using femto-second pulse-probe techniques to measure upper state lifetimes in quantum wells; (3) on studying the optical properties (index of refraction and absorption coefficient) in the vicinity of the intersubband absorption peaks, and on studying bias- and population-induced changes in these properties; and (4) on incorporating quantum-well, tunnel-barrier heterostructures in waveguide geometry optoelectronic devices (modulators, switches, and detectors). The excited state lifetimes in quantum wells are inherently very short (and can be shortened further using their tunnel barriers) so it is anticipated that this research will lead to the realization of faster, lower power devices than are presently available in the 1.5 um spectral range. It is also anticipated that these devices will show superior temperature stability because they are based on intersubband, rather than band-to-band processes. ***
