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An all-optical technique has been used to provide the first direct measurement of anisotropic minority-carrier diffusion in an ordered alloy of GaInP. Direct imaging of the minority-carrier diffusion distribution resulting from generation at a quasipoint source is obtained using an optical microscope coupled to a scanning electron microscope. Minority-carrier diffusion lengths ranging from 3 to 60 μm are measured by this technique in double heterostructures of GaInP, GaAs, and GaInAs, providing a key parameter of interest to the performance of state-of-the-art triple junction solar cells. Here we show a direct measurement of anisotropy in minority-carrier mobility in ordered GaInP, which is evident in the oval-shaped distribution of the recombination luminescence. A factor of 1.6 increase in minority electron mobility along the [110] major axis is reported. [ABSTRACT FROM AUTHOR]

Abstract: An optical technique is used to measure local variations in minority carrier diffusion length associated with dislocation networks in ordered GaInP. Two-dimensional images of the luminescence resulting from carrier generation along a line source are obtained using an optical microscope coupled to a scanning electron microscope. Minority carrier diffusion lengths are determined from the spatial distribution of the recombination luminescence. The use of double heterostructures of AlGaInP/GaInP/AlGaInP restricts diffusion to the plane of the epilayer. Because the technique offers high spatial resolution, it is possible to measure variations in carrier transport associated with the dislocation bands produced due to lattice mismatch with the substrate. Minority carrier diffusion lengths have been correlated to the intensity fluctuations commonly observed in cathodoluminescence across several light and dark bands. In multiple regions of the sample, increased cathodoluminescence intensity occurs in areas of decreased diffusion length. Modeling shows that increased luminescence intensity can correspond to regions of decreased effective minority carrier lifetime, due to the combined effect of variations in non-radiative and radiative recombination rates. [Copyright &y& Elsevier]