OPTICAL CHARACTERIZATION OF SEMICONDUCTOR INTERFACES AND ENVELOPE-FUNCTION MATCHING

Excitons in narrow quantum wells can be used to probe the two interfac es and supply information about their structure. Typical experimental quantities analysed in such studies are the widths of the absorption o r of the photoluminescence lines, the Stokes shifts between them and t he so-called 'monolayer splittings' attributed to the fluctuations of the well width. On the theoretical side, practically all calculations are based on the effective-mass approximation (EMA), and the discrepan cies between theory and experiment are usually attributed to the depar ture of the potential from the ideal square-well shape. Various rapidl y varying modifications of the potential have been used, even though t hey are outside the range of validity of the EMA. In the present paper it is shown that the consistent way of representing the interfaces (b oth perfect and imperfect) is to modify the boundary conditions (BC) f or the envelope functions. The BC at the interfaces have been obtained by several authors from first-principles calculations, but different methods have led to different results. The imperfect ('rough') interfa ces have not been treated in such calculations. Here it is argued that it is better to obtain the sc from the fit to the experiment. One mic roscopic parameter is introduced for each particle (electron, heavy ho le and light hole) and its value can be obtained from the fit to the m onolayer splittings of the optical spectra. This is demonstrated with the example of GaAs/AlGaAs and lnGaAs/lnP narrow quantum wells.