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.

A scanning electron microscope technique is used, in combination with an optical imaging system, to measure minority carrier diffusion length in a heavily doped GaAs double heterostructure. Diffusion and drift of charge are imaged. A diffusion length of 3.6μm is measured, corresponding to a minority carrier mobility of 1150cm2∕Vs in p-type material doped ∼5×1018cm−3. Measurements are made as a function of local electric field and sample temperature. The technique offers a flexible approach to direct measurement of transport properties and is applicable to a range of luminescent materials and multilayer devices.

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