(Color online) Schematic diagram of (a) the GaAs solar cell layer structure, and (b) the trilayer epitaxial protection scheme including the AlAs sacrificial layer.
(Color online) AFM images of the original epi-ready GaAs substrate surface, HF exposed GaAs substrate surface after the epitaxial growth, and removal of protection layers, and the surface without a protection layer. (b) SEM image of an HF exposed wafer surface without protection layers.
(Color online) Hybrid mapping of elemental oxygen, gallium, arsenic near the surface of original, surface protected, and unprotected wafers after the protection layers were removed. The elemental compositions are shown in each image.
(Color online) Energy dispersive spectra of wafers in Fig. 2.
(Color online) X-ray photoelectron emission spectra of the samples in Fig. 2.
(Color online) Atomic resolution cross-sectional transmission electron microscope images of the growth interface between the wafer and epitaxial GaAs layer grown on (a) original, (b) first epitaxial, and (c) second epitaxial growth steps. Dotted lines indicate the starting growth interfaces. Insets show details of the growth interfaces.
(Color online) Photoluminescence spectra at room temperature (300 K) from an Al0.7Ga0.3As/GaAs/ Al0.7Ga0.3As heterostructure on an original and reused wafer. Insets: The 2× and 4× surface reconstruction patterns obtained by reflection high-energy electron diffraction for the original and etched substrate surfaces with and without a protection trilayer.
(Color online) Current density vs voltage (J-V) characteristics under 1 sun, AM1.5 G simulated solar illumination of the GaAs solar cells grown and fabricated on original and reused wafers using protection layers. Inset: Device performance parameters. Here, J sc is the short circuit current, V oc the open circuit voltage, FF the fill factor, and PCE is the power conversion efficiency.
(Color online) EQE of photovoltaic cells grown on original and reused wafers as a function of wavelength. Inset: Short circuit current obtained by integration of the EQE spectrum over a 1 sun, AM1.5 G solar spectrum. Note that these are within experimental error of the directly measured currents in Fig. 8.
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