Green to ultraviolet photoluminescence from CuAl_xGa_1-xS₂ chalcopyrite semiconductor heteroepitaxial alloys grown by low-pressure metalorganic vapor phase epitaxy

CuAl_xGa_1-xS₂ alloy films were successfully grown on GaAs and GaP substrates by low-pressure metalorganic vapor phase epitaxy. All CuAl_xGa_1-xS₂ layers exhibited near-band-edge photoluminescence peaks related to free or bound excitons at 77 and 300 K, which were assigned based on the results of photoreflectance measurements. These excitonic emissions cover the spectral ranges from green to ultraviolet in color by changing CuAlS₂ mole fraction x. The alloy composition was well-controlled using triisobutylaluminum and normal-tripropylgallium as source precursors. All alloy layers were of high quality and had a single domain structure with their c-axes normal to the surface of both GaAs(0 0 1) and GaP(0 0 1) substrates. A remarkable residual tensile biaxial strain was found in the films on both the substrates, which is mainly due to the thermal stress. The strain subsequently caused the increase of the crystal-field splittings in the valence bands. CuAl_xGa_1-xS₂ was shown to have a potential as a proper material for visible and UV light-emitting devices.