| One-dimensional nanomaterials have high specific surface areas, rich surface states and higher surfactant, which show excellent performance both in gas sensors and optoelectronic devices. Based on the excellent performance of one-dimensional nanomaterial devices, many meaningful researches have been carried out in the field. With the decreasing size of nanomaterials, For example, when the diameter is less than 100 nm, the inherent properties of the material will be changed. Compared with larger diameter nanomaterials, small size of nanomaterials have large specific surface areas, which show the quantum confinement effect, as well as unique optical and electrical properties. It has been reported that devices constructed with small size nanowires have the advantages of fast response and high sensitivity.At present, limited by the method of nanowires preparation, device processing and other factors, the diameter of synthesized nanowires are mostly around 100 nm, which is greater than the characteristics width of the surface barrier layer(about 20-40 nm). So, there is a nondepletion layer in the nanowires. With the decrease of the diameter of nanowires, the surface potential barrier cannot be formed. Then nanowires will be completely depleted. All of above will lead to a great increase in the intrinsic resistance of the nanowires. Therefore, The key control factor of the current transport is not the Schottky Barrier, but the intrinsic resistance of the nanowires, which plays an important role in improving the performance of nano-devices. So, the main problem is how to build small-diameter nanowire devices.Based on the above issues, to improve the UV detection of the device, the contents of our research include the following parts:Firstly, we synthesized Cd(OH)2 ultrafine nanowires with the diameter of less than 20 nm with the hydrothermal method. Then Cd(OH)2 ultrafine nanowires decomposed into the CdO ultrafine nanowires. Core-shell structure nanowires were prepared by the reign growth of shell structure on the CdO ultrafine nanowires. Then the morphology and size of ultrafine nanowires of CdO/ZnO core shell structure were characterized by field emission scanning electron microscope(SEM), X-ray diffraction(XRD) and high resolution transmission electron microscope(TEM).Secondly, the current magnitude of devices constructed with CdO ultrafine nanowires under normal temperature is 10-15-10-14, which is in the same order of magnitude as the interference signal of the I-V tester. It doesn't contribute to the electrical transport properties of the core-shell structure, but plays a role in the growth of the template. On the low temperature probe station, we have tested the electrical properties of the CdO/ZnO core-shell structure ultrafine nanowire device constructed by 80 cycles. At the same time, effects of annealing at different temperatures on CdO/ZnO core-shell structure ultrafine nanowire devices were studied. It is concluded that high temperature annealing causes the aggregation of particles and the reorganization of the atomic structure of the surface, which changes the quantity or level position of the surface defect level. The test results of core-shell structure ultrafine nanowire device at low temperature showed that under the small voltage, the current transmission is in accordance with the thermal activation model. The size of the thermal activation energy is 0.14 eV. After annealing 60 min at 500 celsius, with the core-shell structure ultrafine nanowire devices under 0.1 V, I-V test data of temperature variation in high temperature region 220 K-300 K was fitted, and the thermal activation energy was calculated as 0.36 eV.Finally, under the irradiation of ultraviolet(UV), the on-off ratios, response and recovery curves of the devices under different deposition cycles were studied. For the deposition of 80 cycles of ultrafine nanowire devices, the on-off ratio is up to 104. However, the response and recovery time were longer than that of the devices with less deposition cycles. According to the results of the I-V and I-T curves of ultrafine nanowire devices which deposited 80 cycles under UV test at low temperature as well as before and after annealing, reveal that the photocurrent increases gradually with the temperature increases and the recovery time at low temperature is up to 400 s. |
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