Reflectance spectra at 2 °K for the fundamental exciton of pure InP are reported. Both "free" surface and biased Schottky barriers are investigated. It is shown that interference effects, due to various mechanisms of interaction with the surface, have a dominant role in changing the line shape of the excitonic structure, much in the same way as done by electric fields in the Schottky-barrier case. The importance of taking into account the strong spatial inhomogeneity of the surface layer, even in the absence of surface fields, is discussed for both cases of "classical" and spatial dispersion. It is found that, owing to the above features, spatial-dispersion effects may be severely obscured. From the analysis of the measured spectra, a value of 1.4185 eV is derived for the transverse exciton energy and of 4.9 meV for the effective-Rydberg energy.

• Received 31 May 1973

DOI:https://doi.org/10.1103/PhysRevB.9.1516