ULTRAFAST COHERENT OSCILLATIONS OF ELECTRON-WAVE PACKET IN A STEP-DOPED STEPPED QUANTUM-WELL STRUCTURE

The temporal development of an electron wave packet initially photoexc ited in the region with smaller band gap of a stepped quantum well is investigated numerically by directly solving the time-dependent Schrod inger equation. It is shown that, if the photoexcitation region is abo ut 55% to 65% of the total quantum well width, then coherent ultrafast oscillations will occur between the photoexcitation region and the re st of the well region. The period of these ultrafast oscillations incr eases exponentially with the quantum well width. In addition, the osci llation period ranges between 15 fs for a 50 Angstrom quantum well wid th and 700 fs for a 500 Angstrom quantum well width. The above coheren t oscillations are also found to be insensitive to variations in the q uantum well depth. (C) 1998 American Institute of Physics. [S0021-8979 (98)04314-X].