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The on-state current of the transistor can be significantly improved and the I<jats:sub>ON<\/jats:sub>\/I<jats:sub>OFF<\/jats:sub>ratio increases by almost 2 order. The hole mobility is enhanced by 25 times to 227 cm<jats:sup>2<\/jats:sup>V<jats:sup>\u22121<\/jats:sup>s<jats:sup>\u22121<\/jats:sup>. The contact resistance extracted by the transfer length method is 0.365 k\u2126\u2219\u03bcm, which is the lowest value in black phosphorus transistors without degradation of I<jats:sub>ON<\/jats:sub>\/I<jats:sub>OFF<\/jats:sub>ratio. In addition, the I-V curve of the transistor with PGe<jats:sub>x<\/jats:sub>contact is linear compared to that with Ti contact at 80\u2009K, indicating that a metallic ohmic contact is successfully formed. Finally, X-ray photoelectron spectroscopy is used to characterize the PGe<jats:sub>x<\/jats:sub>compound. A signal of P-Ge bond is first observed, further verifying the doping of Ge into BP and the formation of the PGe<jats:sub>x<\/jats:sub>alloy.<\/jats:p>","DOI":"10.1038\/s41598-017-16845-w","type":"journal-article","created":{"date-parts":[[2017,11,28]],"date-time":"2017-11-28T11:13:44Z","timestamp":1511867624000},"update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":19,"title":["Germanium-doped Metallic Ohmic Contacts in Black Phosphorus Field-Effect Transistors with Ultra-low Contact Resistance"],"prefix":"10.1038","volume":"7","author":[{"given":"Hsun-Ming","family":"Chang","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Adam","family":"Charnas","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yu-Ming","family":"Lin","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Peide D.","family":"Ye","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Chih-I","family":"Wu","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7849-773X","authenticated-orcid":false,"given":"Chao-Hsin","family":"Wu","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"297","published-online":{"date-parts":[[2017,12,4]]},"reference":[{"key":"16845_CR1","doi-asserted-by":"publisher","first-page":"66","DOI":"10.1109\/JEDS.2013.2271582","volume":"1","author":"K Schuegraf","year":"2013","unstructured":"Schuegraf, K., Abraham, M. 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