Highly polarized photoluminescence from 2-μm-thick strained GaAs grown on CaF2

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Abstract
Intense photoluminescence was measured in a strained 2‐μm‐thick GaAs film grown on a (100)‐oriented CaF2 substrate. Circular polarization of 77%±2% was obtained at 77 K under excitation with circularly polarized photons below 1.575 eV. For excitation above 1.610 eV the polarization is limited to 30%±2%. These results are clear indications of strain induced splitting between the M j =‖±3/2〉 and the M j =‖± 1/2〉 hole bands. The deduced splitting was 62.5±2.5 meV, corresponding to a stress of the order of −12 kbar. The polarization is maximum for reception energies very close to the excitation. Strained GaAs/CaF2 is thus a good candidate structure for efficient strongly polarized electron sources.