Sandwiched assembly of ZnO nanowires between graphene layers for a self-powered and fast responsive ultraviolet photodetector

Abstract

A heterostructure of graphene and zinc oxide (ZnO) nanowires (NWs) is fabricated by sandwiching an array of ZnO NWs between two graphene layers for an ultraviolet (UV) photodetector. This unique structure allows NWs to be in direct contact with the graphene layers, minimizing the effect of the substrate or metal electrodes. In this device, graphene layers act as highly conducting electrodes with a high mobility of the generated charge carriers. An excellent sensitivity is demonstrated towards UV illumination, with a reversible photoresponse even for a short period of UV illumination. Response and recovery times of a few milliseconds demonstrated a much faster photoresponse than most of the conventional ZnO nanostructure-based photodetectors. It is shown that the generation of a built-in electric field between the interface of graphene and ZnO NWs effectively contributes to the separation of photogenerated electron-hole pairs for photocurrent generation without applying any external bias. Upon application of external bias voltage, the electric field further increases the drift velocity of photogenerated electrons by reducing the charge recombination rates, and results in an enhancement of the photocurrent. Therefore, the graphene-based heterostructure (G/ZnO NW/G) opens avenues to constructing a novel heterostructure with a combination of two functionally dissimilar materials.

Enhanced UV-light detection based on ZnO nanowires/graphene oxide hybrid using cost-effective low temperature hydrothermal process

“…The sensitivity, which is defined as the ratio of photocurrent to the dark current is about 1.7. This value is comparable with the recent excellent reported photodetectors that are synthesized via expensive and complex techniques [45,46,65]. Fig.…”

“…Therefore , photodetectors synthesized at reduced temperatures methods play a key role in cost reduction and open more choices of flexible substrates selection, which are highly desirable in flexible optoelectronics technology. The hydrothermal process is one of the prime candidates that has attracted considerable attention due to its unique advantages such as simplicity, low cost, more controllable and low temperature (< 100 °C) compared with the previously discussed methods. Despite of these research efforts, few reports have studied ZnO-NWs /graphene oxide (GO) sheets system using hydrothermal process, which is likely due to the absence of effective morphological and interfacial control between ZnO nanostructures and graphene [43][44][45][46]. The motivation of this work is to take advantage of the superior optical properties of ZnO nanowires combined with the flexible, transparent and ideal transport properties of graphene into a single device.…”

Enhanced broadband photoresponse of substrate-free reduced graphene oxide photodetectors

“…Quantitatively, the photocurrent is directly proportional to photogenerated carriers, which are generated mainly from the photoelectric effect (PE) and/or PTE contribution. 30,31 For the PTE effect, the photogenerated carriers are further generated by contributions from photoexcited hot carriers. 18 Substrate removal of graphene materials largely reduces the undesirable energy loss of photoexcited hot carriers from surface phonons of the substrate.…”

Oxygen Plasma Surface Activation of Electron‐Depleted ZnO Nanoparticle Films for Performance‐Enhanced Ultraviolet Photodetectors

“…Among different nanostructures, ZnO nanoparticles (ZnO‐NPs) with uniform particle radius close to the Debye length (∼19 nm) have the most favorable morphology to take full advantage of the electron depletion effect, which is the key to high detection performance such as photoresponsivity ( R ), I Ph / I Dark , and detectivity ( D *) of the ZnO‐NP photodetectors, orders of magnitudes higher than that on their bulk counterparts . However, the fabrication of high‐crystallinity ZnO‐NPs is typically time‐consuming through a sequence of processes including synthesis, separation and dispersion of ZnO‐NPs and subsequent assembly of a thin film on target substrates with prepatterned electrodes followed by a thermal posttreatment, making it unattractive for large‐scale production . In particular, these processes are not suitable for monolithic printable devices on functional substrates such as complementary metaloxide semiconductor.…”