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17 June 2009 Correlating buried-finger photodetector for time-of-flight applications
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Abstract
A double-cathode photodetector (DCP) featuring a buried-finger structure to achieve improved separation efficiency is presented. The interleaving comb-shaped cathodes are realized with n-buried implants and they are located in the p-epitaxial layer roughly 1μm below the surface. Based on MEDICI device simulations several layout variations have been realized in a slightly modified BiCMOS process. Best results are achieved with a finger distance of 12μm and a finger width of 1μm: separation efficiencies of 50, 67, and 54% and responsivities of 0.23, 0.47, and 0.38A/W were measured for the optical wavelengths 410nm, 660nm, and 850nm, respectively. All test structures occupy optical active areas of around 100×100μm2. A maximum 3dB-modulation bandwidth of almost 300MHz was measured, while dark currents in the picoampere range are typical for these detectors up to a bias voltage of 5V at room temperature. In the application of a time-of-flight (TOF) distance measurement sensor, the DCP serves as optical detector and correlating device at the same time. Distance measurements up to 6.2m were performed with a 650nm laser source that emitted an average optical power of 1mW using rectangular modulation signals at 10MHz. The standard deviation is better than 1cm up to 3.4m for a total measurement time of 20ms per acquired distance point.
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G. Zach, A. Nemecek, K. Oberhauser, and H. Zimmermann "Correlating buried-finger photodetector for time-of-flight applications", Proc. SPIE 7389, Optical Measurement Systems for Industrial Inspection VI, 738936 (17 June 2009); https://doi.org/10.1117/12.827817
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