The comparison of transient photocurrent spectroscopy measurements of Pulsed Electron Deposited ZnO thin film for air and vacuum ambient conditions

Özdoğan, Mehmet; Yigen, Serap; Çelebi, Cem; Utlu, G.

doi:10.1016/j.tsf.2019.04.030

Cited by 10 publications

(7 citation statements)

References 37 publications

(54 reference statements)

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“…On the other hand, it could be due to too little silver oxide in the film after cooling down to be detected through XRD or XPS techniques. Besides, the appearance of signals in other regions is also consistent with the experimental results of other articles [34,35], which is no anomaly. While relatively fewer amounts of silver atoms diffused from the bottom layer, the XPS peak of silver is difficult to distinguish in the annealed nanostructured film pre-coated with a 1 nm silver layer.…”

Section: Resultssupporting

confidence: 89%

Nanostructured ZnO/Ag Film Prepared by Magnetron Sputtering Method for Fast Response of Ammonia Gas Detection

Zheng

Wen

et al. 2020

Molecules

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Possessing a large surface-to-volume ratio is significant to the sensitive gas detection of semiconductor nanostructures. Here, we propose a fast-response ammonia gas sensor based on porous nanostructured zinc oxide (ZnO) film, which is fabricated through physical vapor deposition and subsequent thermal annealing. In general, an extremely thin silver (Ag) layer (1, 3, 5 nm) and a 100 nm ZnO film are sequentially deposited on the SiO2/Si substrate by a magnetron sputtering method. The porous nanostructure of ZnO film is formed after thermal annealing contributed by the diffusion of Ag among ZnO crystal grains and the expansion of the ZnO film. Different thicknesses of the Ag layer help the formation of different sizes and quantities of hollows uniformly distributed in the ZnO film, which is demonstrated to hold superior gas sensing abilities than the compact ZnO film. The responses of the different porous ZnO films were also investigated in the ammonia concentration range of 10 to 300 ppm. Experimental results demonstrate that the ZnO/Ag(3 nm) sensor possesses a good electrical resistance variation of 85.74% after exposing the sample to 300 ppm ammonia gas for 310 s. Interestingly, a fast response of 61.18% in 60 s for 300 ppm ammonia gas has been achieved from the ZnO/Ag(5 nm) sensor, which costs only 6 s for the response increase to 10%. Therefore, this controllable, porous, nanostructured ZnO film maintaining a sensitive gas response, fabricated by the physical deposition approach, will be of great interest to the gas-sensing community.

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Section: Resultssupporting

confidence: 89%

Nanostructured ZnO/Ag Film Prepared by Magnetron Sputtering Method for Fast Response of Ammonia Gas Detection

Zheng

Wen

et al. 2020

Molecules

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“…It should be due to combination of both effects. In previous work [16], we have shown that in high vacuum, the photo-response was bigger and slower than that in air, confirming the atmospheric adsorbates such as O2 and H2O greatly dominate the photo-responsivity. And, they suppress the effects of defect states.…”

Section: Introductionsupporting

confidence: 52%

“…3 and green emissions according to energy levels difference [29]. Since the excitation energy (3.57 eV) was slightly above the energy bandgap of our samples (~3.26 eV reported in our previous work [16]); therefore, the electrons excited from the VB to the CB as well as shallow defect levels.…”

Section: Resultsmentioning

confidence: 57%

“…In our previous work [16], we have compared the photo-response properties of PEDfabricated ZnO thin film for air and high vacuum environments, and we saw that the photoresponse decreases faster in air (with a ~%45 relative humidity) and reaches initial condition upon turning the light off. When the water molecules are adsorbed with the hydrogen sides on the surface, which are positively charged due to the high electronegativity of oxygen than hydrogen [15], they capture more electrons than oxygen.…”

Section: Resultsmentioning

confidence: 95%

“…During these measurements, the applied voltage between source and drain was kept constant at 0.5 V. To promote desorption of adsorbates which were already adsorbed on the surface in air, the samples were exposed to UV light. The UV irradiation wavelength was specifically selected to be 254 nm (~4.9 eV) since it is energetically sufficient enough to remove chemisorbed O2 and H2O molecules on the surface [19] as well as for generating electron-hole pairs in the depletion regions of ZnO thin film (Eg ~3.26 eV [16]). Time-dependent current variation of B-ZnO thin film photo-conductor was shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

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Mechanisms behind slow photoresponse character of Pulsed Electron Deposited ZnO thin films

Özdoğan

Çelebi

Utlu

2020

Materials Science in Semiconductor Processing

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Zinc Oxide (ZnO) semiconductor is ideal candidates for ultra-violet (UV) photodetector due to its promising optoelectronic properties. Photodetectors based on ZnO nanostructures show very high photoconductivity under UV light, but they are plagued by slow photo-response time as slow as several tens of hours, even more. Most of the studies claimed that atmospheric adsorbates such as water and oxygen create charge traps states on the surface and remarkably increase both the photoconductivity and response time, but there are also limited studies that claiming the defect induced states acting as hole trap centers responsible for these problems. However, the underlying physical mechanism is still unclear.Here we study the effects of both adsorbates and defect-related states on the photo-response character of Pulsed Electron Deposited ZnO thin films. In order to distinguish between these two mechanisms, we have compared the time-dependent photo-response measurements of bare-ZnO and SiO2 encapsulated-ZnO thin film samples taken under UV light and high vacuum. We show that the dominant mechanism of photo-response in ZnO is the adsorption/desorption of oxygen and water molecules even when the measurement is performed in high vacuum. When the samples are encapsulated by a thin SiO2 layer, the adsorption/desorption rates can significantly improve, and the effects of these molecules partially removed.

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Structural and optical properties of ZnO and Ni:ZnO thin films: the trace of post-annealing

Ilkhani

Dejam

2021

J Mater Sci: Mater Electron

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The comparison of transient photocurrent spectroscopy measurements of Pulsed Electron Deposited ZnO thin film for air and vacuum ambient conditions

Cited by 10 publications

References 37 publications

Nanostructured ZnO/Ag Film Prepared by Magnetron Sputtering Method for Fast Response of Ammonia Gas Detection

Nanostructured ZnO/Ag Film Prepared by Magnetron Sputtering Method for Fast Response of Ammonia Gas Detection

Mechanisms behind slow photoresponse character of Pulsed Electron Deposited ZnO thin films

Structural and optical properties of ZnO and Ni:ZnO thin films: the trace of post-annealing

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