ANALYSIS OF A RESONANT-CAVITY ENHANCED GAAS/ALGAAS MSM PHOTODETECTOR

We have developed a new two-dimensional device simulator for heterostructure metal-semiconductor-metal (MSM) photodetectors. We have incorporated a model of multi-layer optics into the simulator and used it to analyze the temporal response of a resonant-cavity enhanced heterostructure with a confining buffer layer and a distributed Bragg reflector (DBR). We show that through fine tuning the layer thicknesses, optical resonance enhancement of the light absorption can be obtained. Theoretically, the maximum external quantum efficiency in this structure can be as high as 99% (without the shadowing effects) for a 0.5-mu-m thick absorbing layer at 829 nm representing a greater than three-fold enhancement over structures with the same absorption and buffer layer but with no buried DBR. Experimental results obtained on diodes with a buffer layer but no buried DBR have been compared to a two-dimensional simulation with an external circuit modeled using SPICE. For devices with 1.0-mu-m fingers and 1.5-mu-m spaces speeds can be increased by at least a factor of two over diodes with no buried buffer layer.