Broadband ZnO Single-Nanowire Light-Emitting Diode

Abstract

We present a novel technique for reliable electrical injection into single semiconductor nanowires for light-emitting diodes and lasers. The method makes use of a high-resolution negative electron-beam resist and direct electron-beam patterning for the precise fabrication of a metallic top contact along the length of the nanowire, while a planar substrate is used as a bottom contact. It can be applied to any nanowire structure with an arbitrary cross section. We demonstrate this technique by constructing the first zinc oxide single-nanowire light-emitting diode. The device exhibits broad sub-bandgap emission at room temperature.Semiconductor devices are found in a myriad of technological applications. These devices were made possible with the development of planar fabrication techniques, which allowed for the accurate control of their physical dimensions and, more importantly, their reproducibility. Semiconductor nanowire structures are now emerging as promising candidates for even further miniaturization, opening the door to interesting new functionalities. 1,2 A powerful hybrid approach for engineering their optical properties by means of lithographic techniques has been reported recently. 3 However, electrical injection into nanowires still remains a technical challenge. 4 In this Letter, we address this issue by demonstrating a new method for achieving reliable electrical injection into a semiconductor nanowire. We show the potential of this technique by constructing the first zinc oxide (ZnO) singlenanowire light-emitting diode (LED). Previous studies on ZnO nanowire LEDs were carried out on large numbers of nanowires simultaneously by defining a metallic contact on a thin film of nanowires. 5,6 ZnO is a large band-gap (E g ) 3.35 eV at 300 K) 7 semiconductor, with several desirable properties for nanowire laser diodes and LEDs, among many other applications. 5,6,[8][9][10] In particular, the high exciton binding energy (60 meV), which is the result of a strong Coulomb interaction between electrons and holes, causes an enhancement of the radiative transition rate in the ultraviolet (UV) part of the spectrum. 9,10 Furthermore, the electronic and optical properties of ZnO nanowires can be tailored by altering the growth conditions, as well as by appropriate post-growth treatment. 11 For example, as-made ZnO nanowires grown on sapphire substrates exhibit a prominent near band-edge UV peak, whereas nanowires grown on graphite flakes exhibit broad subbandgap luminescence. 11 In addition, a single ZnO nanowire can form a resonant cavity with two naturally faceted hexagonal end faces acting as reflecting mirrors. 9 The ZnO nanowires used in this study were grown by vaporizing and condensing a mixture of ZnO and graphite powder on carbon cloth. 11,19,20 The resulting nanowires are n-type, similar to ZnO in bulk or thin films. [15][16][17] Our technique (Figure 1) relies on the use of poly(methyl methacrylate) (PMMA) 22 as a negative resist 12,13 and electrically insulating layer. PMMA is commonly used as a ...

Synthesis and characterisation of controllably functionalised polyaniline nanofibres

“…Recent advances in the design and synthesis of onedimensional nanomaterials, including organic and inorganic nanowires, have attracted much attention [1][2][3][4][5] .…”

A fast sonochemical approach for the synthesis of solution processable ZnO rods

“…9,10 This paper proposes an inexpensive method to generate, on a large scale and at moderate temperature, ZnO thin films and nanostructures with controlled complexity. In a hydrothermal decomposition reaction, a 1:1 molar solution of zinc nitrate, Zn͑NO 3 ͒ 2 ·6H 2 O and hexamethylenetetramine ͑HMTA͒, ͑CH 2 ͒ 6 N 4 is placed in an oven at 90°C for 6 h. Consequently, hydroxide ions are formed by decomposition of HMTA and they react with Zn 2+ to form ZnO ͑CH 2 ͒ 6 N 4 + 6H 2 Normally, ZnO rods have hexagonal polar facets, 10 which are an important element for lasing applications of ZnO structures, as the polar facets at the extremities act as the mirrors of a Fabry-Pérot cavity, while a reduced lateral scattering is guaranteed by the high refractive index of the ZnO ͑n = 2.45͒, with the rod effectively acting as a waveguide. 1,11 An imperfect 1:1 molar ratio of the starting solution may result in an acicular shape of the rods.…”

Effect of Ga-doping on the properties of ZnO nanowire

“…In particular, ZnO nanowires and nanorods grown by vapor deposition techniques and solution-based methods have attracted interest because of their possible applications in optoelectronic devices such as light-emitting diodes, transparent field-effect transistors, UV light detectors, and solar cells. The fabrication of nanoscale devices has become the focus of intensive research in the area of photonics [12][13][14][15][16][17][18][19][20][21][22]. ZnO nanowires grown on Si substrates are well suited for the development of such optoelectronic devices.…”