Photoluminescence of ZnGe0.68Si0.32As2

A ZnGe0.68Si0.32As2 layer epitaxially grown on GaAs was investigated for polarized photoluminescence. The luminescence peaks found around 1.5 eV were attributed to the GaAs substrate. Within our detection limits and with 2.4 eV excitation we could not detect photoluminescence in the energy range between 1.4 and 2.3 eV from the layer. The luminescence characteristics of the layer sample were the same as for the GaAs reference sample except for a small shift of the low energy peak towards higher energies at temperature below 30 K. The luminescence polarization as a function of the excitation energy agrees with the curve found for the reference GaAs samples. The maximum luminescence polarization of 25% is not exceeded. The absorption behavior of the layer indicated an indirect bandgap at approximately 1.55 eV at 10 K. An indirect bandgap can account for the absence of luminescence, however such material is not suitable for an efficient spin polarized electron cathode