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

A GaAs/AlGaAs/GaAs heterostructure metal-semiconductor-metal photodetector (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 importantly, the measured fall time is as short as 23 ps, which is the shortest 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 the 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 HMSM is more than 20% smaller than that of the CMSM. In addition, it is found that the peak impulse response for the HMSM is substantially larger than that of the CMSM under the same operation condition. Two-dimensional simulations and equivalent circuit analysis have been carried out to interpret the observed phenomena and to provide insight into the underlying physics.