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CO Gas Sensor based on E-beam Evaporated ZnO, MgZnO and CdZnO Thin Films: A Comparative Study
摘要： This paper reports a comparative study of electron-beam evaporated ZnO, MgZnO and CdZnO thin film based gas sensor. At room temperature (RT), these semiconductive thin films were deposited on Si/SiO2 substrate and an interdigitated pattern of chromium electrode deposited on these films. Device properties such as structural, optical and electrical have been reported and analyzed. The sensors have been tested at different operating temperatures. At 250 ℃, the sensor shows the best response for CdZnO thin films. We have obtained sensor response 4.86 with response time 15 sec for 100 PPM carbon mono oxide (CO) gas concentration for CdZnO thin film. Based on experimental results, Cd-doped ZnO has been found most suitable among these semiconducting metal oxides, when used as a CO gas sensor. A correlation between structural, optical and electrical properties with these thin films has also been established.
关键词： Thin film,ZnO,MgZnO,CO Gas sensor,CdZnO,E-beam evaporation
更新于2025-09-23 15:23:52
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Optimizing the performance of ZnO/Au/MgZnO/SiO2 sandwich structured UV photodetectors by surface plasmons in Ag nanoparticles
摘要： The dual-wavelength UV photodetector (PD) with sandwich structure of ZnO/Au/MgZnO/SiO2 was fabricated and investigated with an emphasis on the effects of the Ag nanoparticles localized surface plasmons (LSPs). The results demonstrated that the modification in Ag nanoparticle (NP) position played a remarkable influence on the performance of dual-wavelength UV photodetectors. In comparison with decorating Ag NPs on the surface of the PDs, embedding Ag NPs between the MgZnO and ZnO films could improve two peak responsivities (caused by MgZnO and ZnO layers) significantly. By calculating the responsivities enhancement ratio of double layers (MgZnO and ZnO), the results indicated that the enhancement ratio of MgZnO is higher than that of ZnO. This was ascribed to LSPs of energy match with MgZnO which was superior to ZnO. This work described a creative method for increasing the performance of dual-wavelength UV PDs.
关键词： MgZnO,Ag nanoparticles,Dual wavelength,ZnO,Surface plasmons,UV photodetectors
更新于2025-09-23 15:21:01
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Instability of UV Photoresponse in MgZnO Thin Films and Its Improvement by MgO Capping
摘要： Herein, it is shown that the UV photoresponse characteristics of MgZnO thin films deposited by pulsed laser deposition change rapidly with time if the films are exposed to ambient air and that the response can be stabilized significantly by depositing a thin capping layer of MgO on the surface of MgZnO thin film. The decay time of photocurrent in as-deposited MgZnO thin films increases from 1.8 to 229 s and the value of peak responsivity increases by about three orders of magnitude as the film is exposed to air for about 106 s. On application of MgO capping layer, the decay time of the photocurrent marginally increases from (cid:1)0.2 to (cid:1)0.4 s and the value of peak responsivity increases only by one order of magnitude over the span of 106 s, thereafter showing tendency of saturation, implying much better stability in performance. The MgO capping layer is transparent to UV, but acts as a diffusion barrier for oxygen, stabilizing the UV photoresponse.
关键词： UV photoresponse,stability of photoresponse,MgZnO,MgO capping layers
更新于2025-09-23 15:21:01
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Novel ultraviolet photodetector with ultrahigh photosensitivity employing SILAR-deposited ZnS film on MgZnO
摘要： A novel MgZnO/ZnS heterojunction-based ultraviolet (UV) photodetector (PD) with high performance is fabricated by a facile sol-gel process and a successive ionic layer adsorption and reaction (SILAR) method. ZnS is coated onto the MgZnO film as an interface modification layer, which overcomes the drawbacks of the pristine MgZnO photosensitive layer, such as lower carrier mobility and more traps in the material, and greatly enhances UV-light absorption. The type-II heterostructure constructed by work function differences near the interface facilitate the separation of photogenerated carriers. Compared with the MgZnO PD, the optimized heterojunction PD (MgZnO/ZnS-10) yields a dramatically decreased dark current (z1 nA), a remarkable responsivity (900 A/W) and an ultrahigh photo-to-dark current ratio (up to 2.3 (cid:1) 105) under 325 nm light illumination at 5 V bias. These results provide a cost-efficient means for improving the properties of MgZnO PDs, and show the advantages of MgZnO/ZnS heterojunction PDs in UV detection. This study demonstrates that rational construction of novel heterojunctions holds great potential for fabricating high-performance photodetectors.
关键词： Type-II heterostructure,MgZnO,Ultraviolet (UV) photodetector (PD),ZnS
更新于2025-09-23 15:19:57
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A Model for Surface Space Charge Mediated Ultraviolet Photoresponse in MgZnO Thin Films and Its Experimental Verification
摘要： We propose a model based on the evolution of electron and surface charge density to describe the ultraviolet photoresponse in MgZnO thin films. The MgZnO surface contains a high density of surface bound states for electrons due to chemisorption of oxygen molecules, resulting in formation of a surface depletion region. We take into account the change in both conducting volume and electron density in the nondepleted part of the MgZnO thin films upon UV illumination to model temporal variation of photocurrent. We have deposited a set of MgZnO thin films on Al electrodes by pulsed laser deposition at different oxygen pressures to verify the model. With increasing oxygen pressure, dark current, peak responsivity, and response time decreased while the ON?OFF ratio and UV to visible rejection ratio increased, implying different levels of oxygen chemisorption. The proposed model has been successfully used to simulate the temporal decay of the photocurrent in the deposited devices.
关键词： model for photocurrent decay,ultraviolet photoresponse,MgZnO thin films,oxygen chemisorption,surface space charge
更新于2025-09-23 15:19:57
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Violet Light-Emitting Diodes Based on p-CuI Thin Film/n-MgZnO Quantum Dot Heterojunction
摘要： As the lighting technology evolves, the need for violet light-emitting diodes (LEDs) is growing for high color rendering index lighting. The present technology for violet LEDs is based on the high-cost GaN materials and metal?organic chemical vapor deposition process; therefore, there have recently been intensive studies on developing low-cost alternative materials and processes. In this study, for the ?rst time, we demonstrated violet LEDs based on low-cost materials and processes using a p-CuI thin ?lm/n-MgZnO quantum dot (QD) heterojunction. The p-CuI thin ?lm layer was prepared by an iodination process of Cu ?lms, and the n-MgZnO layer was deposited by spin-coating presynthesized n-MgZnO QDs. To maximize the performance of the violet LED, an optimizing process was performed for each layer of p- and n-type materials. The optimized LED with 1 × 1 mm2-area pixel fabricated using the p-CuI thin ?lm at the iodination temperature of 15 °C and the n-MgZnO QDs at the Mg alloying concentration of 2.7 at. % exhibited the strongest violet emissions at 6 V.
关键词： p-CuI thin ?lm,device optimization,violet light-emitting diode,heterojunction,n-MgZnO quantum dot
更新于2025-09-19 17:13:59
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Ionic liquid/ZnO(0001?) single crystal and epitaxial film interfaces studied through a combination of electrochemical measurements and a pulsed laser deposition process under vacuum
摘要： O-Polar ZnO(000%1) single crystals and ZnO and Mg-doped ZnO (MgZnO) films which were subsequently deposited on the ZnO crystals by a pulsed laser deposition (PLD) method were electrochemically investigated through the interfaces with ionic liquid (IL) in a vacuum. The sample surfaces were confirmed to be atomically clean and flat by reflection high energy electron diffraction (RHEED) observation, prior to their electrochemical measurements. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were then performed, and the donor density, flat band potential of these ZnO samples, and the electric double layer capacitance at the IL/ZnO interfaces were successfully evaluated. The flat band potentials of ZnO and MgZnO films were found to shift to more negative potentials relative to those of the single crystal ZnO, with different values for thicker films, respectively. Some possible origins of the different flat band potentials between ZnO and MgZnO films, and their film thickness dependence of the flat band potential will be discussed in this paper.
关键词： vacuum,ZnO,flat band potential,pulsed laser deposition,MgZnO,electric double layer capacitance,ionic liquid,electrochemical measurements
更新于2025-09-12 10:27:22
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Valance band properties of MgZnO thin films with increasing Mg content; phase separation effects
摘要： Mg alloyed ZnO thin films up to 30 % Mg was grown on glass substrate by spray pyrolysis method. Phase separation has been significant in 30% Mg and barely observable 20% Mg incorporated thin films. PL measurements have displayed two emissions in ZnO thin films at energy of 3.26 eV and 2.10 eV which shifts to higher energy by the Mg incorporation. Similarly, bandgap widening in MgZnO thin films has been observed up to 3.71 eV in 15% Mg incorporated thin film. The widening of the band gap has not been followed for the thin films showing phase separation. Valance band maximum (VBM) positions relative to the Fermi level has been measured by UPS and no significant variation according to the vacuum level has been observed. On the other hand, Fermi level gets close to the VBM as the Mg content increases in the thin films.
关键词： MgZnO,XPS on MgZnO,valance band maximum positions in MgZnO,UPS on MgZnO
更新于2025-09-11 14:15:04