Three-dimensional composition reconstruction of InAlAsSb lattice-matched to InP for top cell implementation

An InAlAsSb random alloy grown by molecular beam epitaxy (MBE) to be lattice-matched to InP with an intended bandgap of 1.57 eV, has been analyzed using atom probe tomography (APT). The InAlAsSb material has demonstrated optoelectronic properties that deviate from theoretically predicted values, potentially due to the presence of compositional variation and defects. The mass spectrum displays sharp peaks with minimal molecular evaporation. 3D reconstruction of the film shows no variant regions on the visual inspection length scale. 2D concentration profiles for each element on a 20×20×10 nm
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region of interest (ROI) show compositional variations spanning 2-4 nm, with In and Al segregating opposite each other (i.e. regions of high/low In concentration are low/high in Al content). Frequency distribution analysis indicates that the In distribution for the ROI is statistically nonrandom. Thus, there exists compositional variations in the InAlAsSb film at nanometer length scales, with the behavior of In likely being a main factor in the production of this variation.