Sampling of RF signals with LTG-GaAs based MSM structures

In this work, we study photoconductive sampling of RF signals using metal semiconductor metal structures with low-temperature grown GaAs (LTG-GaAs) as active media. The sampler is a photos witch (PS) embedded in a microwave coplanar waveguide (CPW) and it is triggered by ultra short optical pulses. Both the design of the electrodes and the semiconductor (SC) characteristics are optimized to ensure high RF isolation in the dark state, large electrical bandwidth and a short response-time to optical exciting pulses. We present here a complete set of results concerning device characterization and demonstrate sampling operation. DC electrical characterization, optoelectronical impulse response and sampling of synchronized RF signals are obtained. From these data, we derive important SC material parameters such as electron mobility and lifetime. Finally we also investigate and explain through a phenomenological model the nonlinearities observed in the optoelectronical response of the sampler.