PEAKED NATURE OF EXCITONIC ABSORPTION IN QUANTUM-WELL WIRES OF INDIRECT-GAP SEMICONDUCTORS

We have developed a theory of optical absorption in quantum-well wires made from indirect-gap semi-conductors, such as Si/si1-xGex, in which the final state is the 1s excitonic state in the lowest conduction su bband. The momentum conservation is due to phonons. It is found that t he absorption spectra reproduce the density-of-states function for one -dimensional systems, i.e., show a singularity at threshold in the ide al case. Calculations using a Lorentzian broadening indicate that the peak absorption is larger than the constant absorption in quantum well s and the ratio is enhanced when the wire size is about 10 angstrom.