Preparation and characterization of CuAlxGa1−xSe2 alloy layers grown by low-pressure metalorganic vapor phase epitaxy

CuAlxGa1−xSe2 alloy layers were successfully grown on GaAs(001) by low-pressure metalorganic vapor phase epitaxy. The distribution coefficient of Al was unity. All alloy layers had their c-axis normal to the substrate plane. Exciton resonance energies were determined as a function of x by means of photoreflectance measurements. A quadratic dependence of exciton energies on x was confirmed. The spin-orbit splittings of the epilayers were approximately the same as that of bulk crystals. The magnitudes of crystal-field splittings were larger than that of bulk crystals, and this was explained in terms of residual tensile biaxial strain in the epilayers. The color of the low-temperature photoluminescence (PL) changed from red to crimson, orange, yellow, green, and bluish-purple with increasing x. A peak due to a free-to-acceptor transition was dominant in the PL spectra of the alloy layers. The acceptor ionization energy increased with increasing x, and the result may reflect an increase of the hole effective mass.