Spectrolab has fabricated a direct semiconductor bonded space solar cell with an efficiency of 3S.8% under the AMO space spectrum. Using a similar technology, Spectrolab has achieved as-junction (SJ) direct bonded terrestrial cell with a record efficiency of 38.8% under the one-sun AM1.SG terrestrial spectrum. Efforts to further improve the SJ cell efficiency have focused on development of the top 3 junctions (T3J) grown on GaAs. Experiments with top 3J isotype cells have yielded an improvement of 1 % in current and 100 mV in voltage for the T3J. Spectrolab has also made significant improvements in its direct bonding process. The improved process has increased bond strengths by more than a factor of S and eliminated issues with large voids.

Spectrolab has demonstrated a 2.2/1.7/1.4/1.05/ 0.73 eV 5J cell with an efficiency of 37.8% under 1 sun AM1.5G spectrum and 35.1% efficiency for 1 sun AM0. The top three junctions and bottom two junctions were grown on GaAs and InP substrates, respectively, by metal organic vapor phase epitaxy. The GaAs-and InP-based cells were then direct bonded to create a lowresistance, high-transmissive interface. Both the space and terrestrial cells have high 1 sun V o c between 4.75 and 4.78 V. Initial tests of the terrestrial cells at concentration are promising with efficiencies increasing up to 10× concentration to a maximum value close to 41%.

Epitaxial magnetite (Fe3O4) thin films were deposited by molecular beam epitaxy using molecular oxygen as the oxidant. Films deposited on (001) SrTiO3, (001) MgO, and (001) BaTiO3 surfaces are epitaxial with the film (001) parallel to the substrate (001) and the film ⟨100⟩ parallel to the substrate ⟨100⟩. X-ray magnetic circular dichroism was used to determine the relative Fe2+∕Fe3+ stoichiometry of the magnetite films, which was nearly independent of oxygen partial pressure over the range studied. All films show no in-plane magnetic anisotropy. Coercive fields ranged from 0.019to0.039T and depended on film roughness.

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The magnetic properties of the ferromagnetic semiconductor In 0.98 Mn 0.02 As were characterized by x-ray absorption spectroscopy and x-ray magnetic circular dichroism. The Mn exhibits an atomic-like L 2,3 absorption spectrum that indicates that the 3d states are highly localized. In addition, a large dichroism at the Mn L 2,3 edge was observed from 5-300 K at an applied field of 2T. A calculated spectrum assuming atomic Mn 2+ yields the best agreement with the experimental InMnAs spectrum. A comparison of the dichroism spectra of MnAs and InMnAs show clear differences suggesting that the ferromagnetism observed in InMnAs is not due to hexagonal MnAs clusters. The temperature dependence of the dichroism indicates the presence of two ferromagnetic species, one with a transition temperature of 30 K and another with a transition temperature in excess of 300 K. The dichroism spectra are consistent with the assignment of the low temperature species to random substitutional Mn and the high temperature species to Mn near-neighbor pairs.