Fullerene sensitized silicon for near to mid infrared light detection
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1247-C01-05
Fullerene sensitized silicon for near to mid infrared light detection Gebhard J. Matt1, Mateusz Bednorz1, Thomas Fromherz1, Saeid Zamiri2, Christoph Lungenschmied3, Niyazi Serdar Sariciftci4, Günther Bauer1 1. Institute for Semiconductor Physics, Johannes Kepler University, Linz, Austria. 2. Christian Doppler Laboratory for Surface Optics, Johannes Kepler University , Linz, Austria. 3. Konarka Austria, Linz, Austria. 4. Linz Institute for Organic Solar Cells (LIOS), Johannes Kepler University , Linz, Austria. ABSTRACT We report on a novel light sensing scheme based on a silicon/fullerene-derivative heterojunction that allows the realization of optoelectronic devices for the detection of near to mid infrared radiation. Despite the absent absorption of silicon and the fullerene-derivative for wavelengths beyond 1.1 µm and 0.72 µm, respectively, a hetero-junction of these materials absorbs and generates a photo-current due to absorption in the near to mid infrared. This photocurrent is caused by an interfacial absorption mechanism [1]. Besides its scientific relevance, the simple fabrication process of the hetero-junction (e.g. the fullerene-derivative is deposited by spin-coating on Si) as well as its compatibility with the established and rather cheap CMOS technology makes the presented hybrid approach a promising candidate for widespread applications.
INTRODUCTION Detection of light in the near (NIR) to mid infrared (MIR) spectral range is a technology with many applications such as optical data transmission (1.55 µm), contrast enhancement for imaging systems in foggy environments, and quality control. In essence, the inherent disadvantage of silicon for optoelectronic infrared applications is its transparency beyond a wavelength of 1.1 µm. To overcome this disadvantage, several technologies such as the deposition of (polycrystalline-) germanium on silicon [2, 3, 4] or the usage of in near infrared photo-conductive and soluble nano-particles [5] have been developed. In the latter case, the simple solution processing of a “guest” material [6] to the silicon based “host” is of particular interest. Potential “guest” materials are organic semiconductors. The strengths of this material-class are their solubility, excellent optical properties and the per se tunable chemically structure. In this work, as “guest” material the soluble C60 derivative methano-fullerene [6,6] phenyl-C61 butyric acid methyl ester (PCBM) has been chosen (see Fig. 1a where the chemical structure is depicted). In contrast to pristine C60 , PCBM is soluble up to 5 weight percent in common organic solvents [7]. Due to the large energy gap of fullerenes between the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO), almost no free
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