Measurement of a long diffusion length in a GaAs film improved by metalorganic-chemical-vapor-deposition source purifications

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Abstract
The vacuum metalorganic-chemical-vapor-deposition (Vacuum MOCVD) process was combined with two source purifications to grow p-GaAs epitaxial films of high quality. Theoretical modeling of quantum yield spectra measured on a specially configured n+-p sample determined the minority-carrier electron diffusion length to be 10 μm to within a factor of 2 in the p layer. The p doping was reduced to the 5×1017 cm−3 level to avoid suppression of the diffusion length by Auger recombination. Multiple vacuum sublimations of dicyclopentadienyl magnesium (CP2Mg), the source of Mg for p doping, reduced the contamination by air and by cyclopentadiene (CP) by an order of magnitude. A dry ice/acetone cold trap was operated at slightly below 180-Torr pressure to reduce the water vapor content of arsine, used as the As source, from the hundreds of ppm down level down to the 2 ppm range. The vacuum growth process reduced residual gas contamination. These techniques were combined to grow a p on n GaAs solar cell with an efficiency of 24% at air mass 1.5 (AM1.5).