Transmission electron microscopy analysis of FeAs precipitates formed in GaAs/AlGaAs heterostructures

Cross-sectional transmission electron microscopy of GaAs/Al0.4Ga0.6As heterostructures grown by liquid-phase epitaxy revealed the formation of regularly shaped precipitates in a subsurface layer. They precipitated during furnace annealing at 850 degrees C. The precipitates were FeAs (orthorhombic) crystallites with orientations such as [110] (1 (1) over bar 1)(GaAs)//[101] (010)(FeAs), [110] ((1) over bar 11)(GaAs)//[001] (010)(FeAs), and [110] (1 (1) over bar (1) over bar)(GaAs)//[13 (4) over bar]((3) over bar 10)(FeAs) With respect to the GaAs crystal. The composition of the precipitates was confirmed by energy-dispersive X-ray spectroscopy microanalysis. We presume that the contamination of the heterostructure surface by the Fe atoms, followed by their migration from the surface during annealing, can be responsible for the formation of FeAs precipitates.