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AX-type defects in zinc-doped GaAs(1−x)P(x) on GaAs


GaAsP alloys are potential candidates for ∼ 1.5 to 1.8 eV photovoltaic converters in multijunction solar cells. We use thermally stimulated capacitance, deep level transient spectroscopy, and photocapacitance to characterize defects in p-type GaAs0.83P0.17 and GaAs0.72P0.28 grown lattice-mismatched on GaAs substrates. We observe several features typically associated with DX centers, including persistent photocapacitance, nonexponential thermally-activated capture and escape transients, and large Stokes shifts for optical thresholds. We use secondary ion mass spectroscopy and capacitance versus voltage measurements to ascertain the sulfur and zinc doping profiles in the n+/p diodes. The dramatic decrease in the effective doping concentration with temperature in the unilluminated GaAs0.72P0.28 diode and the magnitude of the capacitance change with illumination indicate that the defect concentration is comparable to the zinc doping, suggesting that zinc may facilitate the formation of AX complexes in this alloy.


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