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Proceedings Paper

Low-capacitance photoconductive detectors for extremely low optical power fabricated by focused ion-beam doping and overgrowth
Author(s): Markus Vitzethum; Martin Ruff; Ralf Schmidt; Peter Kiesel; S. Malzer; Joerg Koch; Andreas Wieck; Gottfried H. Doehler
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Paper 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.

Paper Details

Date Published: 12 June 2001
PDF: 11 pages
Proc. SPIE 4288, Photodetectors: Materials and Devices VI, (12 June 2001); doi: 10.1117/12.429439
Show Author Affiliations
Markus Vitzethum, Friedrich-Alexander-Univ. Erlangen-Nuernberg (Germany)
Martin Ruff, Friedrich-Alexander-Univ. Erlangen-Nuernberg (Germany)
Ralf Schmidt, Friedrich-Alexander-Univ. Erlangen-Nuernberg (Germany)
Peter Kiesel, Friedrich-Alexander-Univ. Erlangen-Nuernberg (Germany)
S. Malzer, Friedrich-Alexander-Univ. Erlangen-Nuernberg (Germany)
Joerg Koch, Ruhr-Univ. Bochum (Germany)
Andreas Wieck, Ruhr-Univ. Bochum (Germany)
Gottfried H. Doehler, Friedrich-Alexander-Univ. Erlangen-Nuernberg (Germany)

Published in SPIE Proceedings Vol. 4288:
Photodetectors: Materials and Devices VI
Gail J. Brown; Manijeh Razeghi, Editor(s)

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