IOP PUBLISHING JOURNAL OF PHYSICS D: APPLIED PHYSICS J. Phys. D: Appl. Phys. 42 (2009) 234007 (11pp) doi:10.1088/0022-3727/42/23/234007 Flexible photonic-crystal Fano filters based on transferred semiconductor nanomembranes Weidong Zhou 1 , Zhenqiang Ma 2 , Hongjun Yang 1 , Zexuan Qiang 1 , Guoxuan Qin 2 , Huiqing Pang 2 , Li Chen 1 , Weiquan Yang 1 , Santhad Chuwongin 1 and Deyin Zhao 1 1 Department of Electrical Engineering, NanoFAB Center, University of Texas at Arlington, TX 76019, USA 2 Department of Electrical and Computer Engineering, University of Wisconsin-Madison, WI 53706, USA E-mail: wzhou@uta.edu and mazq@engr.wisc.edu Received 24 August 2009 Published 17 November 2009 Online at stacks.iop.org/JPhysD/42/234007 Abstract Crystalline semiconductor nanomembranes (NMs), which are transferable, stackable, bondable and manufacturable, offer unprecedented opportunities for unique and novel device applications. We report and review here nanophotonic devices based on stacked semiconductor NMs that were built on Si, glass and flexible PET substrates. Photonic-crystal Fano resonance based surface-normal optical filters and broadband reflectors have been demonstrated with unique angle and polarization properties. Such a low temperature NM stacking process can lead to a paradigm shift on silicon photonic integration and inorganic flexible photonics. (Some figures in this article are in colour only in the electronic version) 1. Introduction Crystalline semiconductor nanomembranes (NMs), which are transferable, stackable, bondable and manufacturable, offer unprecedented opportunities for unique electronic and photonic devices for vertically stacked high density photonic/electronic integration, high performance flexible electronics and flexible photonics. High quality single crystalline silicon NMs (Si NM) have been transferred onto various foreign substrates, such as glass and flexible polyethylene terephthalate (PET) plastics, based on low temperature transfer and stacking processes, developed by various groups [1–7]. In the last few years, significant progress has been made by Ma’s group on record high-speed flexible electronics, and high performance flexible Ge photodetectors, based on transferable Si/SiGe NMs [4, 5, 8]. Many excellent results have also been reported by Lagally et al [6, 9, 10] and Rogers et al [11–14] on the unique electronic, photonic and thermoelectronic and mechanical properties associated with this new class of inorganic flexible semiconductor membrane material system. Recently, employing a slightly modified transfer process, we have jointly demonstrated Fano filters based on patterned Si NMs transferred onto transparent low index glass and flexible PET substrates [15–19]. In this paper, we review and report the design, fabrication and characterization of these unique photonic devices, with focus on the spectral, angular, and polarization properties, based on dispersion engineering [16]. 2. Fano resonant filter design Photonic-crystal slabs (PCSs) are one of the most promising artificial platforms with in-plane periodic modulation of dielectric constant on a wavelength scale. Shown in figure 1(a) is the schematic of a square lattice PCS, where key lattice parameters are denoted as r , a and t , for air hole radius, lattice constant and slab thickness, respectively. The out- of-the-plane optical mode coupling is feasible with the Fano or guided resonance effect [20–23], where these in-plane guided resonances above the lightline are also strongly coupled to out-of-the-plane radiation modes due to phase matching provided by the periodic lattice structure. Therefore, the 0022-3727/09/234007+11$30.00 1 © 2009 IOP Publishing Ltd Printed in the UK