ABSTRACT
Self-powered ultraviolet (UV) photodetectors (PDs) based on ZnO heterojunctions have attracted more attention due to the simple preparation and excellent photoresponse performance without any power supply. The self-powered UV PDs based on NiO nanoflakes/ZnO nanorod arrays (NRs) heterojunctions were fabricated by a low-cost, simple chemical bath deposition (CBD) method. The crystal quality, optical and electronic properties of ZnO NRs is modified by Al3+ ions additions in the precursor solution. The heterojunction devices with ZnO NRs grown in 0.5% Al3+ ions additions precursor solution exhibit a narrow UV spectral selectivity, high photoresponsivity R (85.12 mA/W) and detectivity D* (1.74 × 1012 cm·Hz1/2/W) and a fast response speed (~2 ms) under 378 nm UV light for low intensity irradiance (0.2 mW/cm2) at zero bias. The large built-in electric field of the NiO/ZnO heterojunction with the increased Fermi level of ZnO NRs provide a strong driving force to separate and transfer the photo-generated carriers, decrease the recombination of the carriers and then improve the photoresponse performance of heterojunction devices without external bias.
ABSTRACT
The self-powered ultraviolet photodetectors (UV PDs) have attracted increasing attention due to their potential applications without consuming any external power. It is important to obtain the high-performance self-powered UV PDs by a simple method for the practical application. Herein, TiO2 nanorod arrays (NRs) were synthesized by hydrothermal method, which were integrated with p-type NiO nanoflakes to realize a high performance pn heterojunction for the efficient UV photodetection. TiO x thin film can improve the morphological and carrier transport properties of TiO2 NRs and decrease the surface and defect states, resulting in the enhanced photocurrent of the devices. NiO/TiO2 nanostructural heterojunctions show excellent rectifying characteristics (rectification ratio of 2.52 × 104 and 1.45 × 105 for NiO/TiO2 NRs and NiO/TiO2 NRs/TiO x, respectively) with a very low reverse saturation current. The PDs based on the heterojunctions exhibit good spectral selectivity, high photoresponsivity, and fast response and recovery speeds without external applied bias under the weak light radiation. The devices demonstrate good stability and repeatability under UV light radiation. The self-powered performance could be attributed to the proper built-in electric field of the heterojunction. TiO2 NRs and NiO nanoflakes construct the well-aligned energy-band structure. The enhanced responsivity and detectivity for the devices with TiO x thin films is related to the increased interfacial charge separation efficiency, reduced carrier recombination, and relatively good electron transport of TiO2 NRs.
ABSTRACT
MoS2 with layered structure and distinct physical properties has attracted attention for electronic or optoelectronic devices. The photoelectric response properties of MoS2/ZnO heterojunctions based devices fabricated by spin-coating MoS2 nanosheets solutions on ZnO nanorod arrays (NRs) were investigated. The results revealed that MoS2 nanosheets were vertically aligned on the surface of ZnO NRs and the devices exhibit good photoresponse stability and reproducibility under UV and red light illuminations. The vertically aligned MoS2 nanosheets facilitate the fast photogenerated carrier separation and transport. The devices with few-layered MoS2 nanosheets show a high responsivity and detectivity under UV and red light illuminations, which can be attributed to small contact resistance between MoS2 nanosheets and ZnO NRs. These results provide important insights in the facile fabrication strategy and understanding electronic and optoelectronic devices based on the heterostructures with vertically aligned MoS2.
