Stress effects on excitons bound to shallow acceptors in GaAs

We have performed stress-dependent photoluminescence measurements on excitons bound to neutral shallow acceptors (A⁰X) in GaAs. From their temperature and stress variation three lines (at zero stress) are proved to be due to the decay of (A⁰X) with the J=5/2 state lowest. When low uniaxial stress (0-2 kgmm^-2) is applied these three lines split into 7 or 8 components, although at high stress only one line remains with a stress shift equal to that for the conduction band to acceptor recombination. A theoretical interpretation based on a bonding two-hole state analogous to the H₂ molecule is found to agree well with the data when the effects of a weak crystal field are included. Small deviations between this theory and experiment are presumed to indicate the importance of the antibonding two-hole functions in the (A⁰X) wave function.