Poster abstract

An intriguing aspect of substitutional acceptors in binary semiconductors of zincblende structure is their exact local symmetry. It has been conjectured that there are cases in which the acceptor atom lies not exactly at the substitutional site but slightly off-centre and, furthermore, that the position adopted can be influenced by material factors such as strain and the level of doping. There are very few methods by which this local environment can be investigated. The most promising approach is to study the behaviour in a magnetic field, notably by magnetic resonance or by spin flip Raman scattering (SFRS). We have previously used SFRS extensively to study nitrogen and lithium acceptor centres in wide bandgap II-VI heterostructures and have found that the acceptor centres have the symmetry of the host material, reduced by the biaxial strains induced as a result of lattice mismatch and/or differential thermal contraction. In contrast, we report here work on ZnSe that contains phosphorus: here the SFR spectra from the acceptors show the presence of a strong trigonal field which is additional to the tetragonal field expected due to the biaxial strain of the layer as a whole. The g-values nevertheless remain characteristic of a shallow (valence-band related) hole centre. The most likely explanation is that the acceptor is displaced from the substitutional site towards or away from the nearest cation neighbour. We believe that this is the first unequivocal demonstration of this type of behaviour in such semiconductors.