LIGHT-HOLE - HEAVY-HOLE EXCITON CROSSOVER IN STRAINED ZNS

Near band edge photoluminescence (PL) of ZnS layers MBE-grown on GaP i s investigated at 4.2K under fully strained, partially relaxed and ful ly relaxed conditions. PL peaks are attributed to heavy-hole (hh) or l ight-hole (lh)-related transitions by comparison with the calculated s train shift for the hh and lh bandgaps. It is shown that, while the fr ee-to-bound (e,A(0)) transition retains its hh character over the whol e range from fully strained to fully relaxed conditions, a hh-lh excit on crossover is observed at intermediate strain. This observation is i nterpreted within the hydrogenic model for shallow states by scaling t he hh-related ionisation energies with the lh to hh effective mass rat io and comparing the result with the strain shift of the lh bandgap. V alues for the deformation potentials are derived and compared with the oretical and earlier experimental ones.