12 June 2001 Low-capacitance photoconductive detectors for extremely low optical power fabricated by focused ion-beam doping and overgrowth
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Proceedings Volume 4288, Photodetectors: Materials and Devices VI; (2001) https://doi.org/10.1117/12.429439
Event: Symposium on Integrated Optics, 2001, San Jose, CA, United States
We present a new concept and first results for a photoconducting detector exhibiting extremely high gain and extremely high detectivity. Previously we have demonstrated detectors and optical switches consisting of a n-i-p photodiode whose n-layer is depleted at sufficiently large reverse bias. Under illumination a photovoltage is induced by the photo-generated electrons and holes, accumulated in the n- and p-layer, respectively. We have shown that each photo-generated electron collected in the n-layer contributes about 10 nA to the photoconductive saturation current if the layer is covered with interdigitated `source' and `drain' contacts of about 1 micrometer separation. This signal persists until the photovoltage decays. For low-noise single- or few-electron detection the capacitance of the n-i-p diode has to be minimized. For this purpose we have fabricated n-i-p-structures consisting of crossed p- and n-doped stripes of a few micrometer width. First the (bottom) p-doped stripe is defined by focused Be-ion beam implantation directly into the semi-insulating substrate, followed by MBE-overgrowth with an i- and an n-doped layer. Narrow n-stripes are defined by wet-etching and n-contact fingers are deposited. Room temperature dark currents at a few volts reverse bias are in the low pA- and capacitances in the low fF-range and the expected large photoconductive gain is observed. The photoresponse is independent on the position of the illumination spot on the 50 X 50 micrometer mesa, although the area of crossing stripes is only a few micrometer wide.
© (2001) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Markus Vitzethum, Markus Vitzethum, Martin Ruff, Martin Ruff, Ralf Schmidt, Ralf Schmidt, Peter Kiesel, Peter Kiesel, S. Malzer, S. Malzer, Joerg Koch, Joerg Koch, Andreas Wieck, Andreas Wieck, Gottfried H. Doehler, Gottfried H. Doehler, } "Low-capacitance photoconductive detectors for extremely low optical power fabricated by focused ion-beam doping and overgrowth", Proc. SPIE 4288, Photodetectors: Materials and Devices VI, (12 June 2001); doi: 10.1117/12.429439; https://doi.org/10.1117/12.429439


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