RESEARCH PAPER Optimized spacer layer thickness for plasmonic-induced enhancement of photocurrent in a-Si:H Z. M. Saleh . H. Nasser . E. O ¨ zkol . M. Gu ¨no ¨ven . K. Abak . S. Canli . A. Bek . R. Turan Received: 24 August 2015 / Accepted: 14 October 2015 / Published online: 24 October 2015 Ó Springer Science+Business Media Dordrecht 2015 Abstract Plasmonic interfaces consisting of silver nanoparticles of different sizes (50–100 nm) have been processed by the self-assembled dewetting technique and integrated to hydrogenated amorphous silicon (a-Si:H) using SiNx spacer layers to investigate the dependence of optical trapping enhancement on spacer layer thickness through the enhancements in photocurrent. Samples illuminated from the a-Si:H side exhibit a localized surface plasmon resonance (LSPR) that is red-shifted with the increasing particle size and broadened into the red with the increasing spacer layer thickness. The photocurrent measured in a-Si:H is not only consistent with the red-shift and broadening of the LSPR, but exhibits critical depen- dence on the spacer layer thickness also. The samples with plasmonic interfaces and a SiNx spacer layer exhibit appreciable enhancement of photocurrent compared with flat a-Si:H reference depending on the size of the Ag nanoparticle. Simulations conducted on one-dimensional square structures exhibit electric fields that are localized near the plasmonic structures but extend appreciably into the higher refractive index a-Si:H. These simulations produce a clear red-shift and broadening of extinction spectra for all spacer layer thicknesses and predict an enhancement in photocurrent in agreement with experimental results. The spectral dependence of photocurrent for six plasmonic interfaces with different Ag nanoparticle sizes and spacer layer thicknesses are correlated with the optical spectra and compared with the simulations to predict an optimal spacer layer thickness. Electronic supplementary material The online version of this article (doi:10.1007/s11051-015-3225-9) contains supple- mentary material, which is available to authorized users. Z. M. Saleh  H. Nasser  E. O ¨ zkol  M. Gu ¨no ¨ven  K. Abak  A. Bek  R. Turan Center for Solar Energy Research and Applications (GU ¨ NAM), Middle East Technical University, Ankara, Turkey Z. M. Saleh (&) Department of Physics, Arab American University-Jenin, Jenin, Palestine e-mail: zaki.saleh@aauj.edu; zakimsaleh@yahoo.com H. Nasser  M. Gu ¨no ¨ven  K. Abak  A. Bek  R. Turan Micro and Nanotechnology Program of Graduate School of Natural and Applied Sciences, Middle East Technical University, Ankara, Turkey S. Canli Central Laboratory, Middle East Technical University, Ankara, Turkey A. Bek  R. Turan Department of Physics, Middle East Technical University, Ankara, Turkey 123 J Nanopart Res (2015) 17:419 DOI 10.1007/s11051-015-3225-9