Growth and characterization of GaAs_1-x-ySb_xN_y/GaAs heterostructures for multijunction solar cell applications

The GaAsSbN dilute-nitride alloy can be grown lattice-matched to GaAs with a bandgap of 1 eV, making it an ideal candidate for use in multijunction solar cells. In this work, using molecular beam epitaxy in conjunction with a radio-frequency nitrogen plasma source, the authors focus first on the growth optimization of the GaAsSb and GaAsN alloys in order to calibrate the Sb and N compositions independently of each other. After the optimum growth conditions to maintain two-dimensional growth were identified, the growth of GaAsSbN films was demonstrated. Both a GaAsSb_0.076N_0.018/GaAs heterostructure (100 nm thick) and a GaAsSb_0.073N_0.015/GaAs quantum well (11 nm thick) were grown. X-ray diffraction analysis reveals quite high crystal quality with a small lattice mismatch of 0.13%-0.16%. Secondary ion mass spectrometry profiling revealed that nitrogen was unintentionally incorporated in the GaAs buffer layer during the plasma ignition and stabilization. Nevertheless, a low temperature photoluminescence peak energy of 1.06 eV was measured for the GaAsSbN heterostructure sample while the quantum well emitted photoluminescence at 1.09 eV, which demonstrates promise for realizing 1-eV solar cells.