{"id":830,"date":"2010-06-28T11:08:43","date_gmt":"2010-06-28T15:08:43","guid":{"rendered":"https:\/\/wpmu2.mit.local\/?p=830"},"modified":"2010-06-28T11:08:43","modified_gmt":"2010-06-28T15:08:43","slug":"top-down-fabrication-of-algangan-nanowires","status":"publish","type":"post","link":"https:\/\/wpmu2.mit.local\/top-down-fabrication-of-algangan-nanowires\/","title":{"rendered":"Top-down Fabrication of AlGaN\/GaN Nanowires"},"content":{"rendered":"
\"Figure<\/a>

Figure 1: Square resistance and in-plane biaxial strain as a function of NWs\u2019 diameter. The inset shows a scanning electron microscopy image of NWs with d~70 nm.<\/p><\/div>\n

The frequency performance of
\nAlx<\/sub>Ga1\u2013x<\/sub>N\/GaN high-electron-mobility transistors (HEMTs) has rapidly increased in recent years. Transistors with current gain cut-off frequencies (fT<\/sub>) above 160 GHz and power gain cut-off frequencies (fmax<\/sub>) of more than 300 GHz have been reported [1<\/a>]<\/sup> [2<\/a>]<\/sup>. In spite of these excellent results, the frequency performance of these devices is still far from their theoretical limit. In this project, we are developing nanowire-based nitride HEMTs to overcome these limitations and to explore the maximum frequency of nitride devices [3<\/a>]<\/sup>.<\/p>\n

\"Figure<\/a>

Figure 2: Current measured in TLM devices as a function of SixNy thickness deposited by CVD. The black solid point is the expected value for the current when taking into account the AlGaN\/GaN material removed during the fabrication of the NWs (d~70 nm and pitch ~ 140 nm).<\/p><\/div>\n

Top-down fabrication of horizontal AlGaN\/GaN nanowires (NWs) has been performed on planar AlGaN\/GaN samples grown on a silicon substrate. E-beam lithography and Cl2<\/sub>-based dry-etching were used to define nanowires with diameters (d) in the 30-200-nm range. The transmission line method (TLM) and visible Raman spectroscopy were used to characterize the NWs as well as planar devices. Figure 1 shows the square resistance (Rsq<\/sub>) and in-plane biaxial strain (exx<\/sub>) in the NWs as a function of diameter [4<\/a>]<\/sup>. The Rsq<\/sub> increases exponentially when the NWs\u2019 diameter is reduced. This behavior can be explained by the tensile strain relaxation occurred during the NWs\u2019 fabrication [5<\/a>]<\/sup>. To improve the NWs\u2019 conductivity (d<100 nm), silicon nitride (Six<\/sub>Ny<\/sub>) was deposited by chemical vapor deposition (CVD) on NWs. Figure 2 shows the current measured in TLM devices as a function of Six<\/sub>Ny<\/sub> thickness. A linear increase of the current occurs when the Six<\/sub>Ny<\/sub> thickness increases. For an optimal Six<\/sub>Ny<\/sub> thickness of 45 nm, the current measured through the horizontal assembly of NWs is 8% higher than in planar devices. The characterization of the high-frequency performance of these nanowires is currently underway. It is expected that the large carrier confinement of these devices will allow higher operating frequencies as well as linearity.<\/p>\n

\r\nReferences
  1. T. Palacios, A. Chakraborty, S. Heikman, S. Keller, S. P. DenBaars, and U. K. Mishra, \u201cAlGaN\/GaN high electron mobility transistors with InGaN back-barriers,\u201d IEEE Electron Device Lett.<\/em>, vol. 27, no. 1, pp. 13-15, Jan. 2006. [↩<\/a>]<\/li>
  2. J. W. Chung, W. E. Hoke, E. M. Chumbes, and T. Palacios, \u201cAlGaN\/GaN HEMT with 300-GHz fmax<\/sub>,\u201d IEEE Electron Device Lett.<\/em>, vol. 31, no. 3, pp. 195-197, Mar. 2010. [↩<\/a>]<\/li>
  3. Y. Li, J. Xiang, F. Qian, S. Gradecak, Y. Wu, H. Yan, D. A. Blom, and C. M. Lieber, <\/strong>\u201cDopant-Free GaN\/AlN\/AlGaN radial nanowire heterostructures as high electron mobility transistors<\/a>,\u201d Nano Lett.<\/em>, vol. 6, pp 1468\u20131473, 2006. [↩<\/a>]<\/li>
  4. S. Tripathy, S. J. Chua, P. Chen and Z. L. Miao, J. Appl. Phys.<\/em> <\/strong>92, 3503 (2002). [↩<\/a>]<\/li>
  5. Y. Zhang, I. P. Smorchkova, C.R. Elsass, S. Keller, J. P. Ibbetson, S. Denbaars, U. Mishra, and J. Singh, J. Appl. Phys.<\/em> <\/strong>87, 7981 (2000). [↩<\/a>]<\/li><\/ol><\/div>","protected":false},"excerpt":{"rendered":"

    The frequency performance of AlxGa1\u2013xN\/GaN high-electron-mobility transistors (HEMTs) has rapidly increased in recent years. Transistors with current gain cut-off frequencies…<\/p>\n<\/div>","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[28],"tags":[4073,4074,60],"_links":{"self":[{"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/posts\/830"}],"collection":[{"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/comments?post=830"}],"version-history":[{"count":4,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/posts\/830\/revisions"}],"predecessor-version":[{"id":839,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/posts\/830\/revisions\/839"}],"wp:attachment":[{"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/media?parent=830"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/categories?post=830"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/tags?post=830"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}