Molecular beam epitaxy of metamorphic solar cells on mixed anion graded buffers
(Color online) P composition of samples grown under identical flux ratio at various values of (●). Fit (- - -) with model from Ref. 12. The composition dependence of on is minimized between 650 and .
(Color online) Room temperature PL spectra of a graded buffer collected from various positions on a 4 in. wafer. PL emission wavelength remains nearly constant from center to edge of the graded buffer, indicating minimal -dependent composition variation at .
(Color online) (a) Control of composition changes during mixed anion graded buffer growth. flux (—) is stepped to change the composition of each layer in the buffer while keeping flux (- - -) constant. (b) Samples grown under various flux ratios (◼) show that composition varies linearly with flux ratio at (- - - is linear fit to data).
PVTEM of graded buffers grown at equal to (a) and (b) . Reduced TDD is observed at .
(Color online) (a) Nomarski micrograph of FTs (streaks on surface) with a density of . (b) RHEED pattern along shows chevrons as a result of high-FTD. (c) XSEM of FTs reveals a depth of 100–300 nm.
(Color online) solar cell under (a) zero bias with faceted trench running down image. (b) 2.0 V forward bias. Dark regions around the FT demonstrate the ability of these defects to quench radiative recombination.
Schematic of optimized graded buffer to allow metamorphic growth on GaAs.
(a) XVHAADF microscope image of . Dark regions correspond to Ga-rich domains, while light regions correspond to In-rich domains. (b) XVTEM image looking down the zone reveals strong phase separation contrast when . Insets show the diffraction spots taken at the , interface, and film. (c) XVTEM image shows muted phase separation contrast when .
(Color online) (a) Schematic of metamorphic solar cell structure. (b) L-IV curves for both (—) and (- - -) cells. increases with increasing .
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