Low-capacitance photoconductive detectors for extremely low optical power fabricated by focused ion-beam doping and overgrowth

Markus Vitzethum; Martin Ruff; Ralf Schmidt; Peter Kiesel; S. Malzer; Joerg Koch; Andreas Wieck; Gottfried H. Doehler

doi:10.1117/12.429439

12 June 2001 Low-capacitance photoconductive detectors for extremely low optical power fabricated by focused ion-beam doping and overgrowth

Markus Vitzethum, Martin Ruff, Ralf Schmidt, Peter Kiesel, S. Malzer, Joerg Koch, Andreas Wieck, Gottfried H. Doehler

Author Affiliations +

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

Abstract

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.

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Markus Vitzethum, Martin Ruff, Ralf Schmidt, Peter Kiesel, S. Malzer, Joerg Koch, Andreas Wieck, and 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); https://doi.org/10.1117/12.429439

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KEYWORDS

Promethium

Sensors

Capacitance

Diodes

Doping

Electrons

Ion beams

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