Zeeman spectroscopy of the defect-induced bound-exciton lines in GaAs grown by molecular-beam epitaxy

A Zeeman spectroscopic investigation of the ‘‘defect-induced’’ bound-exciton lines in GaAs grown by molecular-beam epitaxy is presented. The observed magnetic properties are shown to be consistent with exciton recombination at either single acceptor pairs, or double acceptor–isoelectronic-center pairs. The initial state of the recombination has hole angular momentum quantum number $m_J$=±(3/2 and an electron with $m_J$=±1/2, whilst the final state is magnetically inactive, as expected for two holes paired off in the $m_J$=±1/2 acceptor ground state. The symmetry of the defects giving rise to the principal sharp lines is found to be rhombic I. Study of the anisotropy of the Zeeman splittings demonstrates preferential incorporation of the defects with main symmetry axes along [110] in the (1¯10) plane, as opposed to [1¯10] in the (110) plane, thus giving rise to the remarkable polarization of the lines reported previously. Less strongly polarized lines are found to have main symmetry axes along 〈111〉 directions, but again with preferential incorporation in (1¯10) planes. The transitions are shown to arise from σ oscillators at the low-symmetry defects.