{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,24]],"date-time":"2026-03-24T21:06:00Z","timestamp":1774386360490,"version":"3.50.1"},"reference-count":17,"publisher":"MDPI AG","issue":"23","license":[{"start":{"date-parts":[[2019,11,29]],"date-time":"2019-11-29T00:00:00Z","timestamp":1574985600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100010839","name":"GIST","doi-asserted-by":"publisher","award":["GIST Research Institute (GRI) grant in 2019"],"award-info":[{"award-number":["GIST Research Institute (GRI) grant in 2019"]}],"id":[{"id":"10.13039\/501100010839","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>In this paper, we introduce a disk-shaped Ge-on-Si photodetector for refractive-index difference sensing at an operating wavelength of 1550 nm. For the implementation of a small-scale sensor, a Ge layer was formed on top of a Si layer to increase the absorption coefficient at the expense of the light-detection area. Additionally, the sensor had a ring waveguide structure along the edge of the disk formed by a recess into the inner part of the disk. This increased the interaction between the dominant optical mode traveling along the edge waveguide and the refractive index of the cladding material to be sensed, and conclusively increased detection sensitivity. The simulation results show that the proposed sensor exhibited a detection sensitivity of &gt;50 nm\/RIU (Refractive Index Unit), a quality factor of approximately 3000, and a minimum detectable refractive index change of 0.95 \u00d7 10\u22122 RIU with a small disk radius of 3 \u03bcm. This corresponds to 1.67 times the sensitivity without a recess (&gt;30 nm\/RIU).<\/jats:p>","DOI":"10.3390\/s19235253","type":"journal-article","created":{"date-parts":[[2019,11,29]],"date-time":"2019-11-29T10:58:21Z","timestamp":1575025101000},"page":"5253","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Design of Microdisk-Shaped Ge on Si Photodetector with Recess Structure for Refractive-Index Sensing"],"prefix":"10.3390","volume":"19","author":[{"given":"Dongjun","family":"Seo","sequence":"first","affiliation":[{"name":"School of Electrical Engineering and Computer Science, Gwangju Institute of Science and Technology (GIST), 123 Cheomdangwagi-ro, Buk-gu, Gwangju 61005, Korea"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Chang-Soo","family":"Park","sequence":"additional","affiliation":[{"name":"School of Electrical Engineering and Computer Science, Gwangju Institute of Science and Technology (GIST), 123 Cheomdangwagi-ro, Buk-gu, Gwangju 61005, Korea"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4473-6883","authenticated-orcid":false,"given":"Young Min","family":"Song","sequence":"additional","affiliation":[{"name":"School of Electrical Engineering and Computer Science, Gwangju Institute of Science and Technology (GIST), 123 Cheomdangwagi-ro, Buk-gu, Gwangju 61005, Korea"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2019,11,29]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"7994","DOI":"10.1364\/OE.21.007994","article-title":"Silicon photonic micro-disk resonators for label-free biosensing","volume":"21","author":"Grist","year":"2013","journal-title":"Opt. Express"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"5405","DOI":"10.1364\/OL.38.005405","article-title":"Suspended ultra-small disk resonator on silicon for optical sensing","volume":"38","author":"Wang","year":"2013","journal-title":"Opt. Lett."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"15330","DOI":"10.1364\/OE.17.015330","article-title":"Compact SOI nanowire refractive index sensor using phase shifted Bragg grating","volume":"17","author":"Prabhathan","year":"2009","journal-title":"Opt. Express"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"073004","DOI":"10.1088\/2040-8986\/aac75b","article-title":"Photonic crystal resonances for sensing and imaging","volume":"20","author":"Pitruzzello","year":"2018","journal-title":"J. Opt."},{"key":"ref_5","doi-asserted-by":"crossref","unstructured":"Vakili, M., and Noori, M. (2019). A Highly Accurate Refractive index Sensor with Two Operation Modes Based on Photonic Crystal Ring Resonator. Ann. Phys., 531.","DOI":"10.1002\/andp.201800453"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"25688","DOI":"10.1364\/OE.23.025688","article-title":"High-sensitivity liquid refractive-index sensor based on a Mach-Zehnder interferometer with a double-slot hybrid plasmonic waveguide","volume":"23","author":"Sun","year":"2015","journal-title":"Opt. Express"},{"key":"ref_7","first-page":"680227","article-title":"Integrated Optical Chemical Sensor Based on an SOI Ring Resonator Using Phase-Interrogation","volume":"6","author":"Liu","year":"2014","journal-title":"IEEE Photonics J."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"217","DOI":"10.1007\/s13320-017-0418-0","article-title":"A Study on Refractive Index Sensors Based on Optical Micro-Ring Resonators","volume":"7","author":"Tsigaridas","year":"2017","journal-title":"Photonic Sen."},{"key":"ref_9","doi-asserted-by":"crossref","unstructured":"Chrostowski, L., Grist, S., Flueckiger, J., Shi, W., Wang, X., Ouellet, E., Yun, H., Webb, M., Nie, B., and Liang, Z. (2012, January 21\u201326). Silicon photonic resonator sensors and devices. Proceedings of the Laser Resonators, Microresonators, and Beam Control XIV, San Francisco, CA, USA.","DOI":"10.1117\/12.916860"},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Luan, E., Shoman, H., Ratner, D.M., Cheung, K.C., and Chrostowski, L. (2018). Silicon Photonic Biosensors Using Label-Free Detection. Sensors, 18.","DOI":"10.20944\/preprints201809.0150.v2"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"1544","DOI":"10.1039\/c0nr00201a","article-title":"Label-free biological and chemical sensors","volume":"2","author":"Hunt","year":"2010","journal-title":"Nanoscale"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"28517","DOI":"10.1364\/OE.22.028517","article-title":"Silicon-on-insulator sensors using integrated resonance-enhanced defect-mediated photodetectors","volume":"22","author":"Fard","year":"2014","journal-title":"Opt. Express"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"169","DOI":"10.1007\/s10404-017-2007-3","article-title":"Optofluidic sensor system with Ge PIN photodetector for CMOS-compatible sensing","volume":"21","author":"Augel","year":"2017","journal-title":"Microfluid. Nanofluid."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"14166","DOI":"10.1364\/OE.22.014166","article-title":"Performance of ultra-thin SOI-based resonators for sensing applications","volume":"22","author":"Fard","year":"2014","journal-title":"Opt. Express"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"11061","DOI":"10.1364\/OE.15.011061","article-title":"Single mode, polarization-independent submicron silicon waveguides based on geometrical adjustments","volume":"15","author":"Lim","year":"2007","journal-title":"Opt. 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