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Proceedings Paper

FIB-assisted a-SiGe:H/a-SiC:H alloy analysis for ultra-low biased multispectral pixn sensors with enhanced color separation features and low-reflective ZnO:Al back-contacts
Author(s): Andreas Bablich; Krystian Watty; Christian Merfort; Markus Böhm
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Paper Abstract

Common security CCD and CMOS imaging systems are not able to distinguish colorimetrically between dangerous chemical substances, for example whitish powders [1]. Hydrogenated amorphous silicon (a-Si:H) with profiled bandgaps can be found in solar cells to optimize the collection of incoming photons [2]. We developed multicolor photodiodes based on a-Si:H with different spectral response characteristics for a reliable, fast, cheap and non-destructive identification of potentially dangerous substances. Optical and I-V measurements were performed to explore the effect of combining linearly graded a-SiC:H-/a-SiGe:H layers with low reflective aluminum doped zinc oxide (ZnO:Al) cathodes. We determined absorption coefficients and mobility-lifetime products (μτ) of graded and non-graded absorbers to calculate the penetration depth of photons at different energies into the device structure. This set of parameters enables an optimization of the intrinsic layers so that charge accumulations are generated precisely at defined device depths. Significant color separation improvements could be achieved by using ZnO:Al cathodes instead of commonly used ZnO:Al/Chromium (Cr) reflectors. As a result, we obtained multicolor diodes with highly precise adjustment of the spectral sensitivity ranging from 420 nm to 580 nm, reduced interference fringes and a very low reverse bias voltage of -2.5 V maximum. Three terminal device architectures with similar absorbers exhibit a shift from 440 nm to 630 nm by applying reverse voltages of, for instance, -11.5 V at 580 nm [3]. Present research efforts concentrate on further improvements of the absorption region to reduce the bias without affecting the optical sensor performance, using extensive bandgap engineering techniques.

Paper Details

Date Published: 19 May 2012
PDF: 9 pages
Proc. SPIE 8376, Photonic Microdevices/Microstructures for Sensing IV, 83760Q (19 May 2012); doi: 10.1117/12.918318
Show Author Affiliations
Andreas Bablich, Univ. of Siegen (Germany)
Krystian Watty, Univ. of Siegen (Germany)
Christian Merfort, Univ. of Siegen (Germany)
Markus Böhm, Univ. of Siegen (Germany)

Published in SPIE Proceedings Vol. 8376:
Photonic Microdevices/Microstructures for Sensing IV
Xudong Fan; Hai Xiao; Anbo Wang, Editor(s)

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