Performance assessment of low temperature-grown GaAs-based optoelectronic devices dedicated to RF sampling applications

In a previous presentation we have demonstrated the optoelectronic sampling of RF signals using photoswitches (PSW) made from low-temperature grown (LTG) GaAs [1]. The main characteristics that are required for better sampling performances are high optical sensitivity, high bandwidth, large ON/OFF ratio and electrical linearity response. They are closely linked both to the LTG-GaAs properties and to the geometrical design of the RF waveguide. We tested a large set of PSW with different configurations and we present here a complete set of experimental and simulation results. Specially, we point out that using the device with a shortest gap length leads to the generation of frequency harmonics while increasing RF input electrical power. Hence, the spurious free dynamic range (SFDR) is reduced when the RF power is increased up to 13 dBm. We suggest that this results from an electrical nonlinear response which is partially due to carrier velocity saturation in LTG-GaAs. In accordance with [2, 3], we model it and find an electric field saturation of 14 kV/cm.