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Overview of the metamorphic buffer layer growth profile. The homoepitaxial buffer GaAs layer is followed by alloys of a continuous convex compositional gradient of the In content from x = 0% to 53%. The grading comprises of three sections: first 400 nm along a parabolic curve, then linearly, with the slope of the curve reduced for the final 190 nm. The structure is capped with an InP layer, grown under our best established growth conditions as in Ref. 10 .
Schematic cross section of the InAlAs solar cell grown on the metamorphic buffer on a GaAs substrate.
Cross-sectional bright field TEM image of the MBL of the solar cell structure. (A1) GaAs substrate; (A2) 400 nm InxGa1−xAs parabolic grading from 1 to 23% indium; (A3) and (A4) 690 nm InxGa1−xAs linear grading 23% to 53%; (A5) 600 nm InP capping layer.
2-axis X-ray diffractogram of the InAlAs solar cell structure grown on the MBL substrate illustrating diffraction from the GaAs substrate, the metamorphic buffer layers (MBL), and the InAlAs/InP solar cell structure.
Current density vs voltage characteristics as a function of temperature for InAlAs diodes on (a) InP substrate and (b) MBL/GaAs substrates. The inset to (b) plots the data on a linear scale around V = 0 V.
Measured current density–voltage characteristics of the InAlAs devices on InP and GaAs substrates under 1-Sun illumination. Projected performance for large area solar cells is given for both substrate types.
External quantum efficiency as measured for both the InAlAs solar cells grown on the GaAs substrate (diamonds) and mesa diodes on the InP substrate (circles). The simulated responses are given as a straight (GaAs) and dashed line (InP).
Projected AM1.5G photovoltaic performance for In0.52Al0.48As solar cells on InP and GaAs substrates.
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