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Silicon sensitivity for IR sensitive optoelectronic devices is limited by the 1.11 eV band-gap of bulk silicon. Extension of silicon's spectral sensitivity to NIR wavelengths beyond 1250 nm while keeping the CMOS compatibility would be beneficial to possible telecom or other optoelectronic uses. By making heterojunction optoelectronic devices based on thin films of vacuum-deposited organic semiconductors on silicon substrates it is possible to vary the barrier height of the heterojunction, and thus also the spectral response of the devices. By using micro and nano-structured silicon substrates, electronic and optical properties of structured substrates can be used to improve the device performance in comparison to using flat substrates. We present example of heterojunctions based on silicon/organic thin films of hydrogen-bonded pigment tyrian purple (6, 6′-dibromoindigo) formed by vacuum evaporation. Though the band- gap of both materials in the heterojunction is relatively high, our devices show sub silicon- bandgap IR sensitivity up to 2500 nm with responsivity of ~5 mA/W in the telecom C-band [1, 2]. We show how micro- and nano-structuring of silicon substrates prior to vacuum evaporation of organic layer significantly improves the responsivity of hybrid silicon- organic photodiodes. [1] M. Bednorz, G. J. Matt, E. D. Głowacki, T. Fromherz, C. J. Brabec, M. C. Scharber, H. Sitter, and N. S. Sariciftci, Org. Electron. 14 (2013), 1344 [2] V. Đerek, E. Głowacki, M. Sytnyk, W. Heiss, M. Marciuš, M. Ristić, M. Ivanda, and N.S. Sariciftci, Applied Physics Letters, 107 (2015) 083302 |
