Photodetecting properties of single CuO–ZnO core–shell nanowires with p–n radial heterojunction

Abstract

CuO–ZnO core–shell radial heterojunction nanowire arrays were obtained by a simple route which implies two cost-effective methods: thermal oxidation in air for preparing CuO nanowire arrays, acting as a p-type core and RF magnetron sputtering for coating the surface of the CuO nanowires with a ZnO thin film, acting as a n-type shell. The morphological, structural, optical and compositional properties of the CuO–ZnO core–shell nanowire arrays were investigated. In order to analyse the electrical and photoelectrical properties of the metal oxide nanowires, single CuO and CuO–ZnO core–shell nanowires were contacted by employing electron beam lithography (EBL) and focused ion beam induced deposition (FIBID). The photoelectrical properties emphasize that the p–n radial heterojunction diodes based on single CuO–ZnO core–shell nanowires behave as photodetectors, evidencing a time-depending photoresponse under illumination at 520 nm and 405 nm wavelengths. The performance of the photodetector device was evaluated by assessing its key parameters: responsivity, external quantum efficiency and detectivity. The results highlighted that the obtained CuO–ZnO core–shell nanowires are emerging as potential building blocks for a next generation of photodetector devices.

Self-connected CuO–ZnO radial core–shell heterojunction nanowire arrays grown on interdigitated electrodes for visible-light photodetectors

“…Hence, in the last years, core–shell heterojunction nanowires based on metal oxides emerged as promising new materials capable of encoding new and advanced functionalities that are essential for the next generation miniaturized nanowire based photodetectors 25 , 26 . Accordingly, various core–shell heterojunctions were used in order to fabricate photodetectors based on single (ZnO–Cu x O 27 , CuO–ZnO 28 , ZnO/ZnS 29 , ZnO/Ws 2 30 , ZnO/AlN 31 , etc.) or on arrays (ZnO–Cu 2 O 32 , ZnO/CuCrO 2 33 , ZnO/NiO 34 , ZnO–Co 3 O 4 35 , ZnO/SnO 2 36 , ZnO/Ga 2 O 3 37 , ZnO/Si 38 , etc.)…”

“…ZnO is a n-type semiconductor with a wide direct band gap (3.37 eV), large exciton binding energy (60 meV) at room temperature, and high electron mobility (up to 200 cm 2 V −1 s −1 ) 14 . By joining CuO and ZnO into a radial core–shell nanowire configuration, a type II heterojunction is formed, leading to a structure suitable for advanced photodetectors with broad detection range 27 , 28 , 40 . The staggered gap type II heterojunction promotes an efficient charge separation of photogenerated electron–hole pairs along the CuO–ZnO interface, generating a built-in electric field and consequently enhancing the light absorption efficiency 27 , 28 , 40 .…”

“…By joining CuO and ZnO into a radial core–shell nanowire configuration, a type II heterojunction is formed, leading to a structure suitable for advanced photodetectors with broad detection range 27 , 28 , 40 . The staggered gap type II heterojunction promotes an efficient charge separation of photogenerated electron–hole pairs along the CuO–ZnO interface, generating a built-in electric field and consequently enhancing the light absorption efficiency 27 , 28 , 40 . Until now, only a few approaches were used to obtain CuO–ZnO core–shell heterojunction nanowire arrays, the cores consisting in CuO nanowires and the shell being a ZnO thin film entirely covering the surface of the CuO nanowires 28 , 41 – 43 .…”

“…The staggered gap type II heterojunction promotes an efficient charge separation of photogenerated electron–hole pairs along the CuO–ZnO interface, generating a built-in electric field and consequently enhancing the light absorption efficiency 27 , 28 , 40 . Until now, only a few approaches were used to obtain CuO–ZnO core–shell heterojunction nanowire arrays, the cores consisting in CuO nanowires and the shell being a ZnO thin film entirely covering the surface of the CuO nanowires 28 , 41 – 43 . Thus, the CuO nanowires (core) were prepared by thermal oxidation in air 28 , 41 – 44 , while the ZnO thin film shell was obtained by radio-frequency (RF) magnetron sputtering 28 , thermal decomposition 41 – 43 or atomic layer deposition 44 .…”

Near‐Infrared Light Triggered Self‐Powered Mechano‐Optical Communication System using Wearable Photodetector Textile

“…Because Te NWs and TeSe were both p‐type semiconductors, there was a high hole concentration in Te NWs under NIR light, while the hole concentration in the TeSe shell was much lower than the electron concentration, which proved that the type‐II heterojunction between Te and TeSe could drive the migration of photogenerated electrons from Te NWs to the TeSe shell, leaving holes behind. [ 24–26 ] In addition, the electron and hole distributions in Te@TeSe were uneven, and the hole concentration near the Te and TeSe interface was higher than that in the Te center, while the hole concentration distribution was opposite, which proved that traps in TeSe could produce a local positive gating effect. When the device was in the dark, the charge and hole distribution of the device was similar to that under NIR light, the electron concentration in the TeSe shell was higher than the hole concentration, and the hole concentration in Te was higher than the electron concentration, indicating that there was an electric field from Te to TeSe that drove the migration of photogenerated carriers (Figures S10 and S11a, Supporting Information).…”