Positron states and annihilation in nanometric semiconducting superlattices

The electron and positron states in the band structure of GaAs-AlAs, (GaAs)m((AlAs)1-x(vacancy/pore)x)n and (GaAs)m((AlAs)1-xGex)n superlattices have been analyzed on the basis of empirical pseudopotential method of calculations. When possible, the validity of results has been checked by comparing them with the data obtained for relevant constituents of the superlattices with the help of the angular correlation of annihilation radiation (ACAR) spectroscopy. The most important finding is that positron is capable of being selectively confined in the superlattices even when they are defect-free. In the presence of defects of a vacancy-type, the regime of confinement may be changed to the one of trapping of positron. Being 'fingerprints' of certain types of defects, the ACAR spectra may be used for non-destructive characterization of superlattices. The question of sensitivity of the positron particle microprobe for studying electron structure of superlattices is discussed.