Subscriber access provided by Iowa State University | Library
Communication
Photon-Triggered Current Generation in Chemically-Synthesized Silicon Nanowires Jungkil Kim, Ha-Reem Kim, Hoo-Cheol Lee, Kyoung-Ho Kim, MinSoo Hwang, Jung Min Lee, Kwang-Yong Jeong, and Hong-Gyu Park Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.8b04843 • Publication Date (Web): 24 Jan 2019 Downloaded from http://pubs.acs.org on January 25, 2019
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 18 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Nano Letters
Photon-Triggered Current Generation in Chemically-Synthesized Silicon Nanowires Jungkil Kim†,§,‡, Ha-Reem Kim†,‡, Hoo-Cheol Lee†, Kyoung-Ho Kim, Min-Soo Hwang†, Jung Min Lee†, Kwang-Yong Jeong†, and Hong-Gyu Park†,‖,#,* †Department
of Physics, Korea University, Seoul 02841, Korea
§Department
of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
Department
of Physics, Chungbuk National University, Cheongju 28644, Korea
‖KU-KIST
Graduate School of Converging Science and Technology, Korea University, Seoul
02841, Korea #Center
for Molecular Spectroscopy and Dynamics, Institute for Basic Science, Seoul 02841,
Korea ‡These
authors contributed equally to this work
KEYWORDS: photon-triggered current, silicon nanowire, porous silicon, chemical synthesis, photodetector
1 ACS Paragon Plus Environment
Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Abstract: A porous Si segment in a Si nanowire (NW), when exposed to light, generates a current with a high on/off ratio. This unique feature has been recently used to demonstrate photon-triggered NW devices including transistors, logic gates, and photodetection systems. Here, we develop a reliable and simple procedure to fabricate porous Si segments in chemicallysynthesized Si NWs for photon-triggered current generation. To achieve this, we employ 100nm-diameter chemical-vapor-deposition grown Si NWs that possess an n-type high doping level and extremely smooth surface. The NW regions uncovered by electron-beam resist become selectively porous through metal-assisted chemical etching, using Ag nanoparticles as a catalyst. The contact electrodes are then fabricated on both ends of such NWs, and the generated current is measured when the laser is focused on the porous Si segment. The current level is changed by controlling the power of the incident laser and bias voltage. The on/off ratio is measured up to 1.5 × 104 at a forward bias of 5 V. In addition, we investigate the porous-length-dependent responsivity of the NW device with the porous Si segment. The responsivity is observed to decrease for porous segment lengths beyond 360 nm. Furthermore, we fabricate nine porous Si segments in a single Si NW and measure the identical photon-triggered current from each porous segment; this single NW device can function as a high-resolution photodetection system. Therefore, our fabrication method to precisely control the position and length of the porous Si segments opens up new possibilities for the practical implementation of programmable logic gates and ultrasensitive photodetectors.
2 ACS Paragon Plus Environment
Page 2 of 18
Page 3 of 18 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Nano Letters
Semiconductor nanowire (NW) transistors are being developed as essential components of future electronic devices.1-9 In particular, NW transistors enabled significant development of nano- or nano-bio-electronics including programmable NW circuits for logic gates and nanoprocessors2,10,11 and highly sensitive bio-probes to detect, stimulate and inhibit neuronal signals.3,12-15 Free-standing kinked NW transistor probes provide new possibilities for NW applications in intracellular recordings.16,17 In addition, the three-dimensional macroporous nanoelectronic networks using NW transistors allow for in-vivo multiplexed recording and stimulation of neural activities and can be used as minimally invasive brain probes.18-20 More recently, a new NW transistor has been demonstrated, in which optical switching and amplification of electrical currents were achieved without an electrical gate.21 This photontriggered NW transistor consists of porous Si (PSi) segments embedded in a single crystalline Si (CSi) NW, which were fabricated via metal-assisted chemical etching (MaCE) of a moderate ndoped Si wafer. The current level between the source and drain contact electrodes is efficiently controlled under the illumination of a pump laser. While the injected carriers are trapped in the localized states of the PSi segment and the current is blocked in the dark condition, the trapped carriers are excited into higher electronic states triggering a current across the electrodes in the illuminated condition.21 However, to extend the functionality of the device, a simple procedure is required to fabricate PSi segments with desired lengths and positions in chemically-synthesized Si NWs with a high doping level and smooth surface. In this study, our new fabrication technique enables the generation of numerous PSi segments in a single Si NW synthesized using the chemical vapor deposition (CVD) system. The PSi segments are analyzed using the images obtained from scanning electron microscopy (SEM) and transmission electron microscopy 3 ACS Paragon Plus Environment
Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
(TEM). The current-voltage (I-V) characteristics and responsivities are systematically measured in the devices fabricated using Si NWs with PSi segments of different lengths. We also demonstrated a high-resolution photodetection system by integrating multiple PSi segments into a single Si NW. We used a chemically-synthesized single Si NW with a high n-type doping level and an ultrasmooth surface (see Methods in Supporting Information).22,23 First, the Si NWs with diameters of ~100 nm were dispersed onto the Si3N4/SiO2/Si substrate (Figure 1a). To form a PSi segment at a desired position of the Si NW, a polymethyl methacrylate (PMMA) layer of 400 nm thickness was coated on the NW, and then a PMMA window was opened using an electron-beam lithography technique (Figure 1b). Next, the two-step MaCE was performed: In the first step, the entire NW structure was immersed into a solution mixture of hydrofluoric acid, silver nitrate, and deionized (DI) water, resulting in the decoration of the exposed Si NW surface with Ag nanoparticles (AgNPs) (Figure 1c) (see Methods in Supporting Information). In the second step, the NW was immersed into an etching solution containing hydrofluoric acid, hydrogen peroxide, and DI water (Figure 1d) (see Methods in Supporting Information). Consequently, only the NW segment with the AgNP-decorated surface becomes selectively porous.
4 ACS Paragon Plus Environment
Page 4 of 18
Page 5 of 18 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Nano Letters
Figure 1. (a)–(d) Schematic illustrations showing the fabrication procedure of a PSi segment in a chemically-synthesized single Si NW. (a) A single Si NW of ~100 nm in diameter is dispersed onto the Si3N4/SiO2/Si substrate. (b) The whole structure is spin-coated with a 400-nm-thick PMMA layer, and the selected NW region is exposed to air by using an aligned electron-beam lithography technique. (c) AgNPs are decorated on the exposed surface of the Si NW by immersing the NW into a mixture solution of hydrofluoric acid, silver nitrate, and DI water ([HF]:[AgNO3]:[H2O] = 1:0.005:100) for 20 s at room temperature. (d) The NW segment with the AgNP-decorated surface becomes selectively PSi, on immersing the NW into the etching solution ([HF]:[H2O2]:[H2O] = 1:1.5:10) for 20 s at room temperature. (e),(f) SEM images of the NW in the fabrication steps of (c) and (d), respectively. (e) Numerous AgNPs, a few nanometers in size, are decorated on the NW surface in the exposed PMMA region. The NW diameter is 100 nm. Scale bar, 100 nm. (f) The PSi segment is formed in the Si NW with the AgNP-decorated surface. The length of the PSi segment is ~360 nm. Scale bar, 100 nm.
We analyzed the detailed NW structure during each step of the MaCE by using SEM. In the first step, a number of AgNPs of size
