ANALYSIS OF THE PHASE SIGNAL IN REFLECTION ANISOTROPY SPECTROSCOPY

In this study the analysis of reflection anisotropy signals reveals th at an unusual behaviour of the phase signal may occur in the presence of weakly anisotropic surfaces. It will be shown that the measured lin eshape has to be considered with extreme care if a single-phase lock-i n amplifier is used in the experimental set-up. It not only depends on the sample properties but is also influenced by the experimental cond itions, in particular the signal phase, which is usually adjusted for maximum signal before spectra are taken and then fixed during measurem ent. For this purpose the reflection anisotropy spectra are compared w ith those of the phase for various semiconductor systems. Ideally one would expect the phase signal to change by 180 degrees whenever the re flection anisotropy signal changes sign. On the contrary it was found that the phase spectra, e.g. from the cubic semiconductor GaSb(100), e xhibit continuous phase shifts near the zeros in the reflection anisot ropy spectra when measuring the signal at twice the modulation frequen cy. The reflection anisotropy spectra may therefore be significantly d ifferent if measured with distinct phases. Theoretical considerations and further experiments reveal that this effect is likely to be caused by partial polarization, which is hard to avoid in any experimental s et-up.