Ge-on-Si Photonics for Mid-infrared Sensing Applications
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Ge-on-Si Photonics for Mid-infrared Sensing Applications K. Gallacher1, L. Baldassarre2, A. Samarelli1, R. W. Millar1, A. Ballabio3, J. Frigerio3, G. Isella3, A. Bashir4, I. MacLaren4, V. Giliberti2, G. Pellegrini5, P. Biagioni5, M. Ortolani2, D. J. Paul1 1
University of Glasgow, School of Engineering, Rankine Building, Oakfield Avenue, Glasgow,
G12 8LT, U.K 2
Center for Life NanoScience@Sapienza, Sapienza Università di Roma and Istituto Italiano di Tecnologia, Viale Regina Elena 291, I-00161 Rome, Italy
3
L-NESS, Dipartimento di Fisica del Politecnico di Milano, Polo Territoriale di Como, Via
Anzani 42, I-22100 Como, Italy 4
University of Glasgow, School of Physics and Astronomy, Kelvin Building, University Avenue,
Glasgow G12 8QQ, U.K.. 5
Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133 Milano,
Italy
ABSTRACT There is significant interest to develop cheap CMOS compatible sensors that operate in the mid-infrared (MIR). To meet these requirements, Ge-on-Si is proving to be an exciting platform. There is the potential to realize waveguide integrated quantum well infrared photodetectors (QWIPs) based on Ge quantum wells (QWs). Intersubband absorption from p-Ge QWs has been demonstrated in the important atmospheric transmission window of 8-13 µm. An alternative strategy for sensing in the MIR is demonstrated through highly n-type doped Ge plasmonic antennas. These antennas demonstrate vibrational sensing of polydimethylsiloxane (PDMS) spin coated layers at 12.5 µm wavelength. These demonstrate enhanced sensing capabilities due to the localized hot spots of the antenna resonant modes. INTRODUCTION There is significant interest to develop cheap and practical detectors that cover the important transmission windows within the mid-infrared (3-5 and 8-13 µm wavelength) to enable on-chip biological and gas sensing spectroscopic detectors. Currently the gold standard for detection at these wavelengths is mercury-cadmium-telluride (MCT) due to the inherently large detectivities from interband absorption [1]. The disadvantages with MCT are that it is fragile, has low process uniformity, is not easily integrated with Si and the toxic elements have been banned for use in civilian products in Europe. InSb gas detectors are now available in the 3 to 5 µm window but the material is fragile and difficult to process [2]. This paper will discuss two potential routes for detection based on the Ge on Si material platform.
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Recently it has been demonstrated that p-Ge quantum wells (QWs) can provide strong absorption in the 8-13 µm wavelength range through intersubband absorption [3]. These p-Ge QW superlattice structures can be strain symmetrised past critical thickness limitations and therefore provide large absorption coefficients. Initial experimental results
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