Direct Integration of Metal Oxide Nanowire in Vertical Field-Effect Transistor

Abstract

We demonstrate seamless direct integration of a semiconductor nanowire grown using a bottom-up approach to obtain a vertical field-effect transistor (VFET). We first synthesize single crystalline semiconductor indium oxide (In 2 O 3 ) nanowires projecting vertically and uniformly on a nonconducting optical sapphire substrate. Direct electrical contact to the nanowires is uniquely provided by a self-assembled underlying In 2 O 3 buffer layer formed in-situ during the nanowire growth. A controlled time-resolved growth study reveals dynamic simultaneous nucleation and epitaxial growth events, driven by two competitive growth mechanisms. Based on the nanowire-integrated platform, a depletion mode n-channel VFET with an In 2 O 3 nanowire constituting the active channel is fabricated. Our unique vertical device architecture could potentially lead to tera-level ultrahigh-density nanoscale electronic, and optoelectronic devices.Bottom-up nanofabrication approaches involving direct interfacing and integration of low-dimensional nanostructures, in particular vertically aligned one-dimensional (1D) nanowires, could potentially provide an attractive solution to attain ultrahigh-density advanced nanoscale devices and 3D nanocircuitries. 1 To realize and maximize the true potential of these nanostructures for advanced applications in nanoelectronics and optoelectronics, reproducible synthesis of 1D nanowires with controlled directionality and morphology is critical. Equally important, a means of providing ideal and direct electrical interface to the nanowires 2 without disrupting their structural integrity would facilitate subsequent nanoscale device integration and realization of good device performance.Indium oxide is a direct wide band gap semiconductor (E g ∼ 3.55-3.75 eV) transparent oxide. 3 It finds several applications ranging from transparent conductive electrodes to electrochromic mirrors and gas sensors. 4 More recently, research has been conducted on indium oxide nanostructures, predominantly nanowires, for potential applications in highsensitivity sensor, optoelectronic, field-emission, electronic, and memory devices. [5][6][7] Various synthesis approaches have been demonstrated, which include vapor transport 8 and laser ablation 9 on a variety of substrates. However, common to other nanowire syntheses, growth directionality control (with respect to the substrate) and direct integration (on the same substrate) into functional devices remain as two significant challenges. To avoid the usual pick-and-place methods of manipulating and aligning horizontally lying nanowires to fabricate prototype testing platforms, 10,11 a proposed solution is to grow single crystalline nanowires epitaxially on a latticematched substrate with the major nanowire growth direction orthogonal to the substrate plane and to use this integrated platform for direct device fabrication. Ideally, the substrate also should be electrically conductive; however, potential substrates that meet both requirements are not readily available. Afte...

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