STUDIES OF HIGH-SPEED METAL-SEMICONDUCTOR-METAL PHOTODETECTOR WITH A GAAS ALGAAS/GAAS HETEROSTRUCTURE/

A GaAs/AlGaAs/GaAs heterostructure metal-semiconductor-metal photodete ctor (HMSM), with an active area of 100 x 100 mum2, has been developed and studied. The measured rise time of the device is 30 ps. More impo rtantly, the measured fall time is as short as 23 ps, which is the sho rtest reported for an MSM photodetector of similar size. The observed ultrafast response is attributed to the reduction of both the carrier transit time and the device capacitance due to the incorporation of th e AlGaAs barrier layer. The HMSM is found to have a smaller saturation capacitance and saturates at a much lower bias voltage in comparison with the conventional MSM photodetector (CMSM). At a bias of 10 V, the full width at half maximum (FWHM) of the temporal response of the HMS M is more than 20% smaller than that of the CMSM. In addition, it is f ound that the peak impulse response for the HMSM is substantially larg er than that of the CMSM under the same operation condition. Two-dimen sional simulations and equivalent circuit analysis have been carried o ut to interpret the observed phenomena and to provide insight into the underlying physics.