ZnO-Cu2O core-shell nanowires as stable and fast response photodetectors

Abstract

In this work, we present all-oxide p-n junction core-shell nanowires (NWs) as fast and stable self-powered photodetectors. Hydrothermally grown n-type ZnO NWs were conformal covered by different thicknesses (up to 420 nm) of p-type copper oxide layers through metalorganic chemical vapor deposition (MOCVD).The ZnO NWs exhibit a single crystalline Wurtzite structure, preferentially grown along the [002] direction, and energy gap Eg=3.24 eV. Depending on the deposition temperature, the copper oxide shell exhibits either a crystalline cubic structure of pure Cu2O phase (MOCVD at 250 C) or a cubic structure of Cu2O with the presence of CuO phase impurities (MOCVD at 300 C), with energy gap of 2.48 eV.The electrical measurements indicate the formation of a p-n junction after the deposition of the copper oxide layer. The core-shell photodetectors present a photoresponsivity at 0V bias voltage up to 7.7 µA/W and time response ≤0.09 s, the fastest ever reported for oxide photodetectors in the visible range, and among the fastest including photodetectors with response limited to the UV region. The bare ZnO NWs have slow photoresponsivity, without recovery after the end of photo-stimulation. The fast time response for the core-shell structures is due to the presence of the p-n junctions, which enables fast exciton separation and charge extraction. Additionally, the suitable electronic structure of the ZnO-Cu2O heterojunction enables self-powering of the device at 0V bias voltage. These results represent a significant advancement in the development of low-cost, high efficiency and self-powered photodetectors, highlighting the need of fine tuning the morphology, composition and electronic properties of p-n junctions to maximize device performances.

Si/CuIn0.7Ga0.3Se2 Core–Shell Heterojunction for Sensitive and Self‐Driven UV–vis–NIR Broadband Photodetector

“…When the electron–hole pairs are generated under illumination, the built‐in electric field will separate and transfer them to electrodes instantly. Therefore, the core–shell structure will effectively convert light signals into electrical signals even at zero external bias voltage …”

Recent Progress of Heterojunction Ultraviolet Photodetectors: Materials, Integrations, and Applications

“…Many heterojunctions are integrated just by simple methods such as sputtering, direct transferring, and spin‐coating 13,29,153–159. It is a much more flexible way to combine various materials of different dimensions.…”

Fast Multifrequency Measurement of Nonlinear Conductance

“…We demonstrate the method in the context of conductive atomic force microscopy, acquiring IVCs at every pixel while scanning at standard imaging speed.The sensitive measurement of small currents in nanometer-scale junctions is a central problem in modern experimental physics. Characterization of numerous novel materials and devices, in applications ranging from topological quantum computers [1, 2] to energy harvesting and energy conversion [3][4][5][6][7][8][9][10], struggles with the same basic limitations imposed by the small measurement current and the large stray capacitance of the macroscopic leads. We describe how to circumvent these limitations using phase-coherent multifrequency lock-in measurement and inverse Fourier transform to achieve a dramatic improvement in the speed of measurement, or alternatively, in the signal-to-noise ratio at the same measurement speed.…”