Plasmon-enhanced ZnO-based nanowire heterojunction array photodetector

Objective Low-dimensional ZnO-based photodetectors have high responsivity and high photon absorption ability. However, the limited absorption range and reduced carrier lifetime of ZnO constrain its potential applications in optoelectronics. This study presents a novel plasmon-enhanced photodetector with zinc oxide (ZnO) nanowires-zinc selenide (ZnSe) heterojunction arrays.

Methods One-dimensional (1D) ZnO nanowires with ZnSe shell heterostructures were synthesized on FTO substrate using low-temperature hydrothermal and chemical vapor deposition methods. Subsequently, silver nanoparticles were uniformly deposited on the heterojunction through capillary self-assembly, resulting in a plasmon-enhanced heterojunction array photodetector (Fig.1). The built-in electric field within the heterostructure accelerates the effective separation of photogenerated electrons and holes, thereby promoting the charge carrier transport characteristics of the optoelectronic device. Leveraging the surface plasmon resonance effect, noble metal nanoparticles exhibit excellent localized field enhancement, effectively enhancing the material's light absorption. Material morphology, structure, and chemical composition were characterized through scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray spectroscopy (XRD), and Raman spectroscopy analyses. The photovoltaic characteristics of the detector were systematically analyzed using standard techniques such as the chopped light voltammetry method, optoelectronic transient response measurement, and time-current curves.

Results and Discussions Under visible light irradiation, the photoresponsivity of the Ag nanoparticle-enhanced ZnO/ZnSe heterojunction nanowire array photodetector far exceeds that of the ZnO/ZnSe heterojunction nanowire array photodetector and the ZnO nanowire array photodetector, reaching a maximum of 2.8 mA/W (Fig.3). At a bias voltage of 0.8 V and under visible light irradiation at 100 mW/cm², the responsivity of the Ag nanoparticle-enhanced ZnO/ZnSe heterojunction nanowire array photodetector is approximately 52 times higher than that of the pure ZnO nanowire array photodetector, with a responsivity of 1.71 mA/W (Fig.4). This indicates that the formation of the heterostructure, coupled with Ag nanoparticle modification, indeed promotes the separation of photogenerated electron-hole pairs in the photodetector, enhancing the material's photodetection ability. Compared to the pure ZnO nanowire array photodetector, the ZnO/ZnSe heterojunction nanowire array photodetector exhibits significantly enhanced absorption in the range of 400 nm to 600 nm. Furthermore, the Ag nanoparticle-enhanced ZnO/ZnSe heterojunction nanowire array photodetector demonstrates an approximately 5-fold increase in absorbance within the wavelength range of 400 nm to 800 nm (Fig.5). This indicates that the formation of the heterostructure broadens the device's spectral response range. The presence of Ag nanoparticles not only extends the detector's spectral response range but also greatly enhances the intensity of light absorption. The optoelectronic transient testing system reveals that the average rise time of 1D ZnO nanowires is reduced by approximately 32% after modification (τ_rise=1.812 ms). The average delay time (τ_delay) has decreased from the original 3.357 ms to 1.803 ms, representing a reduction of about 54%. This substantial improvement in response speed is illustrated (Fig.7). The current curve of the photodetector over time was tested, and the plasmon-enhanced ZnO/ZnSe heterojunction array photodetector maintained 48% of its photocurrent density after 10 hours of illumination, indicating favorable operational longevity. Compared to the initially fabricated device, the photodetector maintained approximately 52% of its photocurrent density after prolonged exposure to air (15 months), highlighting its robust long-term stability (Fig.8).

Conclusions  Compared with the detector based on pure ZnO nanowire array, the detector has excellent photoelectronic performance. Under visible light, the photodetector demonstrates responsivity of 1.7 mA/W and average rise/delay times of 1.812 ms (1.803 ms), exhibiting exceptional stability over 10 hours of continuous testing. This provides a cost-effective, scalable approach for developing high-performance photodetectors, with promising applications in wearable devices, optical communication systems, environmental sensors, etc.