Positron probing of electron momentum density in GaAs-AlAs superlattices and related materials

The band structure calculations based on the method proposed by Jaros et al. (Phys. Rev. B 31, 1205 (1985)) have been performed for the defect-free GaAs-AlAs superlattice and related AlAs and GaAs single crystals; the electron-positron momentum density distributions have been computed and analyzed. The results of calculations are in good agreement with the experimental data obtained ad hoc for GaAs and AlAs bulk materials by measuring the angular correlation of the annihilation radiation (ACAR). Small (but marked) features of the electron-positron momentum density of the valence band have been revealed both for constituent materials and GaAs-AlAs superlattice. The delocalization of positron in 'perfect' defect-'free' AlAs and GaAs single crystals to be observed experimentally is borne out by the results of pseudo-potential band calculations performed on the basis of method proposed by Sekkal et al. (Superlattices and Microstructures, 33, 63 (2003)). The prediction of the possibility of a certain confinement of positron in the interstitial area of GaAs- AlAs superlattice is confirmed by the agreement between the results of calculations and relevant experimental data obtained for GaAs and AlAs single crystals. No considerable effect of the enhancement of the annihilation rate (due to electron-positron interaction) upon the electron-positron momentum density distribution both in the superlattice and its constituent bulk materials has been found. The results of ACAR measurements and calculations performed suggest that a tangible improvement of the sensitivity of existing positron annihilation techniques is necessary for studying details of the electron-positron momentum density distributions in defect-'free' superlattices to be created on the basis of the diamond-like semiconductors possessing close values of the electron momentum densities. On the contrary, the positron-sensitive vacancy-type defects of various types in the superlattice may become a source of the annihilation radiation whose momentum density distribution has its own peculiarities, different from the ones to be detected for defect-'free' crystal structure. Being a 'fingerprint' of a certain type of defects these peculiarities make it possible the nondestructive characterization of the heterostructures and superlattices by means of the positron particle microprobe. (author)