High‐Performance Integrated ZnO Nanowire UV Sensors on Rigid and Flexible Substrates

Abstract

Due to the large surface area‐to‐volume ratio and high quality crystal structure, single nanowire (NW)‐based UV sensors exhibit very high on/off ratios between photoresponse current and dark current. Practical applications require a large‐scale and low‐cost integration, compatibility to flexible electronics, as well as reasonably high photoresponse current that can be detected without high‐precision measurement systems. In this paper, NW‐based UV sensors were fabricated in large‐scale by integrating multiple NWs connected in parallel via the contact printing method. Linear scaling of the photoresponse current with the number of NWs is demonstrated. Integrated ZnO NW UV sensors were fabricated on rigid glass and flexible polyester (PET) substrates at the macroscopic scale. The flexible and rigid sensors performed comparably, exhibiting on/off current ratios approximately three orders of magnitude higher than sensors made from polycrystalline ZnO thin films. Under UV irradiance of 4.5 mW cm−2 and 3 V bias, photoresponse currents and on/off current ratios for the rigid and flexible UV sensors reached 12.22 mA and 82 000, and 14.1 mA and 120 000, respectively. This result suggests that lateral integration of semiconductor NWs is an effective approach to large‐scale fabrication of flexible NW sensors that inherit the merits of single‐NW‐based systems with unaffected performance compared to using rigid substrate.

Screen printed ZnO ultraviolet photoconductive sensor on pencil drawn circuitry over paper

“…Once the UV exposure is turned off, it takes some time to drain out all those photogenerated electrons. This is the reason behind faster current rise time and much slower photocurrent decay, but it is still fast enough in comparison with recent reports 19 on ZnO based flexible UV sensors. In summary, ZnO NCs were obtained by a green, high throughput and solution-based procedure to fabricate UV sensors.…”

Flexible Ultraviolet and Ambient Light Sensor Based on a Nanomaterial Network Fabricated Using Selective and Localized Wet Chemical Reactions

“…[45][46][47] The bandgap energy of ZnO is 3.37 eV that corresponds to a wavelength of 365 nm. 21 Thus, ZnO can show responses to different intensities of UV light by photoconductive effect, which is related to the electron-hole pair generation and chemisorption/desorption of oxygen on the surface of the sensing materials. 48 In the dark state, oxygen molecules are chemisorbed on the ZnO surface as O 2 -ions by capturing free electrons from the ZnO, and this generates a depletion layer near the surface.…”

“…[17][18][19] In particular, ZnO is an n-type semiconductor material with a wide direct bandgap energy of 3.37 eV and large exciton binding energy of 60 meV, which makes it an outstanding material for photonic sensing in the UV range. 20 S. Bai, et al 21 fabricated…”

Photodetector fabrication by dielectrophoretic assembly of GaAs nanowires grown by a two-steps method

“…In this regard, contactless NW manipulation methods using electromagnetic fields -like dielectrophoresis (DEP)-are usually much softer than mechanical methods such as contact transfer printing or tape peeling, often resulting less destructive. Different assembly methods have been developed to manipulate NWs, including fluidic alignment, roll contact printing [15,16], Langmuir-Blodgett (LB) film deposition technique, drop-casting [17,18], nano-manipulation [19,20], and dielectrophoresis [21][22][23][24][25][26]. Fluidic alignment, roll contact printing transfer, and LB techniques, all offer the ability to align NWs in parallel but do not allow for precise NW placement in functional systems.…”