Near-ultraviolet zinc oxide nanowire sensor using low temperature hydrothermal growth

Abstract

Two near-ultraviolet (UV) sensors based on solution-grown zinc oxide (ZnO) nanowires (NWs) which are only sensitive to photo-excitation at or below 400 nm wavelength have been fabricated and characterized. Both devices keep all processing steps, including nanowire growth, under 100 °C for compatibility with a wide variety of substrates. The first device type uses a single optical lithography step process to allow simultaneous in situ horizontal NW growth from solution and creation of symmetric ohmic contacts to the nanowires. The second device type uses a two-mask optical lithography process to create asymmetric ohmic and Schottky contacts. For the symmetric ohmic contacts, at a voltage bias of 1 V across the device, we observed a 29-fold increase in current in comparison to dark current when the NWs were photo-excited by a 400 nm light-emitting diode (LED) at 0.15 mW cm(-2) with a relaxation time constant (τ) ranging from 50 to 555 s. For the asymmetric ohmic and Schottky contacts under 400 nm excitation, τ is measured between 0.5 and 1.4 s over varying time internals, which is ~2 orders of magnitude faster than the devices using symmetric ohmic contacts.

Characterization and modeling of a ZnO nanowire ultraviolet photodetector with graphene transparent contact

“…6 One particular advantage of ZnO nanowires is that it is a low-cost material that can be solution-synthesized on a vast variety of substrates. [7][8][9] A giant photoconductive gain of 10 8 leading to very high detector responsivity has been reported in single nanowire ZnO photodetectors and attributed to hole trapping at the nanowire surface due to oxygen chemisorption. 10 It has been demonstrated that the nanowire surface passivation allows to reach high detectivity values, while maintaining high responsivity of the detector.…”

Focused Energy Field Method for the Localized Synthesis and Direct Integration of 1D Nanomaterials on Microelectronic Devices

“…We demonstrated the synthesis of zinc oxide nanowires (ZnO NWs) by using FEF method. ZnO NWs are one of the most useful 1D nanomaterials for a variety of applications including photodetection, light‐emitting diode, photocatalyst, piezoelectric energy conversion, photovoltaic energy conversion, and field effect transistor . Furthermore, the protocols for low‐temperature hydrothermal synthesis of ZnO NWs are quite well‐established .…”

Drop‐cast and dye‐sensitized ZnO nanorod‐based visible‐light photodetectors

“…As the bias voltage was increased from 10 V to 15 V, the on/off ratio was gradually increased from 17.9 to 77.4. Furthermore, the decay time was dramatically decreased at the applied bias voltage of 15 V. For analyzing the recovery characteristics, the reset time ( τ ) is considered by I = ( I max – I dark ) e – t / τ , where I max and I dark are the dark and maximum current 12. In fact, the transient curves of the 1D single ZnO‐based photodetectors have exhibited two‐ or three‐order exponential decay nature 2, 8.…”

“…It is well known that the photogenerated electron–hole pairs and desorption of oxygen molecules in 1D ZnO nanostructures contribute to the electron–hole pairs at the surface during UV illumination, which induces a photoconductivity 7–9. Accordingly, many studies have been focused on the fabrication and characterization of 1D ZnO nanostructure‐based UV photodetectors by using the chemical vapor deposition (CVD), vapor–liquid–solid process, and hydrothermal synthesis method 10–12. In order to form semiconductor–metal contacts, however, a somewhat complicated process and accurate control for the connections between the metal electrodes have been required until now.…”

“…Single ZnO nanowire could be contacted selectively to metal electrodes by transferring metal patterns onto the ZnO nanowires 3. Otherwise, ZnO NRs were grown laterally for bridging between two patterned electrodes: Au patterned substrate was heated in a quartz tube furnace by CVD method 13 or ZnO seed layer/Au patterned substrate were immersed into growth solution by hydrothermal method 12.…”