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Ordered Arrays of Dual-Diameter Nanopillars for Maximized Optical Absorption
Fan, Zhiyong,Kapadia, Rehan,Leu, Paul W.,Zhang, Xiaobo,Chueh, Yu-Lun,Takei, Kuniharu,Yu, Kyoungsik,Jamshidi, Arash,Rathore, Asghar A.,Ruebusch, Daniel J.,Wu, Ming,Javey, Ali American Chemical Society 2010 Nano letters Vol.10 No.10
<P>Optical properties of highly ordered Ge nanopillar arrays are tuned through shape and geometry control to achieve the optimal absorption efficiency. Increasing the Ge materials filling ratio is shown to increase the reflectance while simultaneously decreasing the transmittance, with the absorbance showing a strong diameter dependency. To enhance the broad band optical absorption efficiency, a novel dual-diameter nanopillar structure is presented, with a small diameter tip for minimal reflectance and a large diameter base for maximal effective absorption coefficient. The enabled single-crystalline absorber material with a thickness of only 2 μm exhibits an impressive absorbance of ∼99% over wavelengths, λ = 300−900 nm. These results enable a viable and convenient route toward shape-controlled nanopillar-based high-performance photonic devices.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2010/nalefd.2010.10.issue-10/nl1010788/production/images/medium/nl-2010-010788_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl1010788'>ACS Electronic Supporting Info</A></P>
Ultrathin compound semiconductor on insulator layers for high-performance nanoscale transistors
Ko, Hyunhyub,Takei, Kuniharu,Kapadia, Rehan,Chuang, Steven,Fang, Hui,Leu, Paul W.,Ganapathi, Kartik,Plis, Elena,Kim, Ha Sul,Chen, Szu-Ying,Madsen, Morten,Ford, Alexandra C.,Chueh, Yu-Lun,Krishna, Sanj Nature Publishing Group, a division of Macmillan P 2010 Nature Vol.468 No.7321
Over the past several years, the inherent scaling limitations of silicon (Si) electron devices have fuelled the exploration of alternative semiconductors, with high carrier mobility, to further enhance device performance. In particular, compound semiconductors heterogeneously integrated on Si substrates have been actively studied: such devices combine the high mobility of III??V semiconductors and the well established, low-cost processing of Si technology. This integration, however, presents significant challenges. Conventionally, heteroepitaxial growth of complex multilayers on Si has been explored??but besides complexity, high defect densities and junction leakage currents present limitations in this approach. Motivated by this challenge, here we use an epitaxial transfer method for the integration of ultrathin layers of single-crystal InAs on Si/SiO<SUB>2</SUB> substrates. As a parallel with silicon-on-insulator (SOI) technology, we use ??XOI?? to represent our compound semiconductor-on-insulator platform. Through experiments and simulation, the electrical properties of InAs XOI transistors are explored, elucidating the critical role of quantum confinement in the transport properties of ultrathin XOI layers. Importantly, a high-quality InAs/dielectric interface is obtained by the use of a novel thermally grown interfacial InAsO<SUB>x</SUB> layer (~1?nm thick). The fabricated field-effect transistors exhibit a peak transconductance of ~1.6?mS?쨉m<SUP>??1</SUP> at a drain??source voltage of 0.5?V, with an on/off current ratio of greater than 10,000.
Nanoscale Semiconductor “X” on Substrate “Y” – Processes, Devices, and Applications
Madsen, Morten,Takei, Kuniharu,Kapadia, Rehan,Fang, Hui,Ko, Hyunhyub,Takahashi, Toshitake,Ford, Alexandra C.,Lee, Min Hyung,Javey, Ali WILEY‐VCH Verlag 2011 ADVANCED MATERIALS Vol.23 No.28
<P><B>Abstract</B></P><P>Recent advancements in the integration of nanoscale, single‐crystalline semiconductor ‘X’ on substrate ‘Y’ (XoY) for use in transistor and sensor applications are presented. XoY is a generic materials framework for enabling the fabrication of various novel devices, without the constraints of the original growth substrates. Two specific XoY process schemes, along with their associated materials, device and applications are presented. In one example, the layer transfer of ultrathin III–V semiconductors with thicknesses of just a few nanometers on Si substrates is explored for use as energy‐efficient electronics, with the fabricated devices exhibiting excellent electrical properties. In the second example, contact printing of nanowire‐arrays on thin, bendable substrates for use as artificial electronic‐skin is presented. Here, the devices are capable of conformably covering any surface, and providing a real‐time, two‐dimensional mapping of external stimuli for the realization of smart functional surfaces. This work is an example of the emerging field of “<I>translational nanotechnology</I>” as it bridges basic science of nanomaterials with practical applications.</P>
Quantum Confinement Effects in Nanoscale-Thickness InAs Membranes
Takei, Kuniharu,Fang, Hui,Kumar, S. Bala,Kapadia, Rehan,Gao, Qun,Madsen, Morten,Kim, Ha Sul,Liu, Chin-Hung,Chueh, Yu-Lun,Plis, Elena,Krishna, Sanjay,Bechtel, Hans A.,Guo, Jing,Javey, Ali American Chemical Society 2011 NANO LETTERS Vol.11 No.11
<P>Nanoscale size effects drastically alter the fundamental properties of semiconductors. Here, we investigate the dominant role of quantum confinement in the field-effect device properties of free-standing InAs nanomembranes with varied thicknesses of 5–50 nm. First, optical absorption studies are performed by transferring InAs “quantum membranes” (QMs) onto transparent substrates, from which the quantized sub-bands are directly visualized. These sub-bands determine the contact resistance of the system with the experimental values consistent with the expected number of quantum transport modes available for a given thickness. Finally, the effective electron mobility of InAs QMs is shown to exhibit anomalous field and thickness dependences that are in distinct contrast to the conventional MOSFET models, arising from the strong quantum confinement of carriers. The results provide an important advance toward establishing the fundamental device physics of two-dimensional semiconductors.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2011/nalefd.2011.11.issue-11/nl2030322/production/images/medium/nl-2011-030322_0003.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl2030322'>ACS Electronic Supporting Info</A></P>
p‐Type InP Nanopillar Photocathodes for Efficient Solar‐Driven Hydrogen Production
Lee, Min Hyung,Takei, Kuniharu,Zhang, Junjun,Kapadia, Rehan,Zheng, Maxwell,Chen, Yu‐,Ze,Nah, Junghyo,Matthews, Tyler S.,Chueh, Yu‐,Lun,Ager, Joel W.,Javey, Ali WILEY‐VCH Verlag 2012 Angewandte Chemie Vol.124 No.43
<P><B>Perfekte Textur</B>: Der Einfluss der Oberflächen‐Nanotexturierung, der TiO<SUB>2</SUB>‐Passivierung und des Ru‐Cokatalysators auf die photoelektrochemische Wasserstoffentwicklung durch p‐InP‐Photokathoden wurde untersucht. Höhere Stromdichten und günstigere Onset‐Potentiale werden nach Oberflächen‐Nanotexturierung beobachtet. NHE=Normalwasserstoffelektrode.</P>
Ergen, Onur,Ruebusch, Daniel J.,Fang, Hui,Rathore, Asghar A.,Kapadia, Rehan,Fan, Zhiyong,Takei, Kuniharu,Jamshidi, Arash,Wu, Ming,Javey, Ali American Chemical Society 2010 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.132 No.40
<P>Highly regular, single-crystalline nanopillar arrays with tunable shapes and geometry are synthesized by the template-assisted vapor−liquid−solid growth mechanism. In this approach, the grown nanopillars faithfully reproduce the shape of the pores because during the growth the liquid catalyst seeds fill the space available, thereby conforming to the pore geometry. The process is highly generic for various material systems, and as an example, CdS and Ge nanopillar arrays with square, rectangular, and circular cross sections are demonstrated. In the future, this technique can be used to engineer the intrinsic properties of NPLs as a function of three independently controlled dimensional parameters - length, width and height.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2010/jacsat.2010.132.issue-40/ja1052413/production/images/medium/ja-2010-052413_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja1052413'>ACS Electronic Supporting Info</A></P>
Roll-to-Roll Anodization and Etching of Aluminum Foils for High-Throughput Surface Nanotexturing
Lee, Min Hyung,Lim, Namsoo,Ruebusch, Daniel J.,Jamshidi, Arash,Kapadia, Rehan,Lee, Rebecca,Seok, Tae Joon,Takei, Kuniharu,Cho, Kee Young,Fan, Zhiyoung,Jang, Hwanung,Wu, Ming,Cho, Gyoujin,Javey, Ali American Chemical Society 2011 Nano letters Vol.11 No.8
<P>A high-throughput process for nanotexturing of hard and soft surfaces based on the roll-to-roll anodization and etching of low-cost aluminum foils is presented. The process enables the precise control of surface topography, feature size, and shape over large areas thereby presenting a highly versatile platform for fabricating substrates with user-defined, functional performance. Specifically, the optical and surface wetting properties of the foil substrates were systematically characterized and tuned through the modulation of the surface texture. In addition, textured aluminum foils with pore and bowl surface features were used as zeptoliter reaction vessels for the well-controlled synthesis of inorganic, organic, and plasmonic nanomaterials, demonstrating yet another powerful potential use of the presented approach.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2011/nalefd.2011.11.issue-8/nl201862d/production/images/medium/nl-2011-01862d_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl201862d'>ACS Electronic Supporting Info</A></P>