HIGHLY POLARIZED PHOTOLUMINESCENCE FROM 2-MU-M-THICK STRAINED GAAS GROWN ON CAF2

Intense photoluminescence was measured in a strained 2-mu m-thick GaAs film grown on a (100)-oriented CaF2 substrate. Circular polarization of 77%+/-2% was obtained at 77 K under excitation with circularly pola rized photons below 1.575 eV. For excitation above 1.610 eV the polari zation 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, correspondi ng to a stress of the order of -12 kbar. The polarization is maximum f or reception energies very close to the excitation. Strained GaAs/CaF2 is thus a good candidate structure for efficient strongly polarized e lectron sources.