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Published online by Cambridge University Press: 17 March 2011
GaAs saturable absorber materials are used in ultrafast nonlinear optics to obtain all-optical switching in optoelectronic devices. They are introduced to semiconductor saturable absorber mirrors (SESAMs) for the generation of ultrashort laser pulses. GaAs is grown on CaF2 by molecular beam epitaxy to fabricate devices, which provide a large high reflection bandwidth. The CaF2 surface was exposed to high- and low-energy electron irradiation before and during growth to increase the surface free energy for the subsequent GaAs overgrowth. A three-layer GaAs/ fluoride device was designed and fabricated to study the impact of the electron exposure on the growth mode and the surface roughness. The surface morphology of an optoelectronic device can cause nonsaturable losses, which degrade the device performance. Therefore, the effect of the electron exposure of the CaF2 layer on the surface roughness of the device was studied by atomic force microscopy. Measurements of the scattered light from the device surface allowed for a quantitative analysis of the nonsaturable losses attributed to the surface morphology of the device.