A series of Zn_(1-x)Cd_xO thin films have been fabricated on sapphire by pulsed-laser deposition(PLD), successfully. To investigate the effect of Cd concentration on structural and optical properties of Zn_(1-x)...A series of Zn_(1-x)Cd_xO thin films have been fabricated on sapphire by pulsed-laser deposition(PLD), successfully. To investigate the effect of Cd concentration on structural and optical properties of Zn_(1-x)Cd_xO films, x-ray diffraction(XRD),ultraviolet-visible spectroscopy(UV-vis), and x-ray photoelectron spectroscopy(XPS) are employed to characterize the films in detail. The XRD pattern indicates that the Zn_(1-x)Cd_xO thin films have high single-orientation of the c axis. The energy bandgap values of ZnCdO thin films decrease from 3.26 eV to 2.98 eV with the increasing Cd concentration(x)according to the(αhν)~2–hν curve. Furthermore, the band offsets of Zn_(1-x)Cd_xO/ZnO heterojunctions are determinated by XPS, indicating that a type-I alignment takes place at the interface and the value of band offset could be tuned by adjusting the Cd concentration.展开更多
We report the fabrication and characterization of light-emitting diodes based on n-ZnO/p-GaN heterojunctions. The n-type ZnO epilayer is deposited by metalorganic chemical vapor deposition (MOCVD) on a MOCVD grown M...We report the fabrication and characterization of light-emitting diodes based on n-ZnO/p-GaN heterojunctions. The n-type ZnO epilayer is deposited by metalorganic chemical vapor deposition (MOCVD) on a MOCVD grown Mg-doped p-GaN layer to form a p-n heterojunction. During the etching process, the relation between the etching depth and the etching time is linear in a HF and NH4 CI solution of a certain ratio. The etching rates of the SiO2 and ZnO are well controlled,which are essential for device fabrication. The current-voltage relationship of this heterojunction shows a diode-like rectifying behavior. In contrast to previous reports,electroluminescence (EL) emissions are observed by the naked eye at room temperature from the n-ZnO/p-GaN heterojunction under forward-and reverse-bias. The origins of these EL emissions are discussed in comparison with the pho- toluminescence spectra.展开更多
n-ZnO/p-GaN heterojunction light-emitting diodes with and without a Ga2O3 interlayer are fabricated. The electroluminescence (EL) spectrum of the n-ZnO/p-GaN displays a single blue emission at 430 nm originating fro...n-ZnO/p-GaN heterojunction light-emitting diodes with and without a Ga2O3 interlayer are fabricated. The electroluminescence (EL) spectrum of the n-ZnO/p-GaN displays a single blue emission at 430 nm originating from GaN, while the n-ZnO/Ga2O3/p-GaN exhibits a broad emission peak from ultraviolet to visible. The broadened EL spectra of n-ZnO/Ga2O3/p-GaN are probably ascribed to the radiative recombination in both the p-GaN and n-ZnO, due to the larger electron barrier (ΔEC=1.85 eV) at n-ZnO/Ga2O3 interface and the much smaller hole barrier (ΔEV=0.20 eV) at Ga2O3/p-GaN interface.展开更多
Metal oxide semiconductor materials such as ZnO have tremendous potential as light absorbers for photocatalysed electrodes in the electrochemical reduction of water. Promoters such as rGO have been added to reduce the...Metal oxide semiconductor materials such as ZnO have tremendous potential as light absorbers for photocatalysed electrodes in the electrochemical reduction of water. Promoters such as rGO have been added to reduce the recombination losses of charge carriers and improve its photoelectrochemical activity. In this study, the effect of layer ordering on the charge transfer properties of rGO-hybridised ZnO sandwich thin films for the photo-catalysed electrochemical reduction of water was investigated. rGO-hybridised ZnO sandwich thin films were prepared via a facile electrode position technique using a layer-by-layer approach. The thin films were analysed using FESEM, XRD, Raman, PL, UV–vis, EIS and CV techniques to investigate its morphological, optical and electrochemical properties. The FESEM images show the formation of distinct layers of rGO and ZnO nanorods/flakes via the layer-by-layer method. XRD confirmed the wurtzite structure of ZnO. PL spectroscopy revealed a reduction of photoemission intensity in the visible region(580 nm) when rGO was incorporated into the ZnO thin film. Among the six thin films prepared, ZnO/rGO showed superior performance compared to the other thin films(0.964 m A/cm) due to the presence of graphene edges which participate as heterogenous electrocatalysts in the photocatalysed electrolysis of water. rGO also acts as electron acceptor, forming an n-p heterojunction which improves the activity of ZnO to oxidise water molecules to O2. EIS revealed that the application of rGO as back contact(rGO/ZnO, rGO/ZnO/rGO) reduces the charge transfer resistance of a semiconductor thin film. Alternatively, rGO as front contact(ZnO/rGO, rGO/ZnO/rGO) improves the photo-catalysed electrolysis of water through the participation of the rGO edges in the chemical activation of water. The findings from this study indicate that the layer ordering significantly affects the thin film's electrostatic properties and this understanding can be further advantageous for tunable applications.展开更多
Heteroepitaxial undoped ZnO films were grown on Si (100) substrates by radio-frequency reactive sputtering, and then some of the samples were annealed at N2-800℃ (Sample 1, S1) and 02-800℃ (Sample 2, S2) for 1...Heteroepitaxial undoped ZnO films were grown on Si (100) substrates by radio-frequency reactive sputtering, and then some of the samples were annealed at N2-800℃ (Sample 1, S1) and 02-800℃ (Sample 2, S2) for 1 h, respectively. The electrical transport characteristics of a ZnO/p-Si heterojunction were investigated. We found two interesting phenomena. First, the temperature coefficients of grain boundary resistances of S 1 were positive (positive temperature coefficients, PTC) while that of both the as-grown sample and S2 were negative (negative temperature coefficients, NTC). Second, the I-V properties of S2 were similar to those common p-n junctions while that of both the as-grown sample and S 1 had double Schottky barrier behaviors, which were in contradiction with the ideal p-n heterojunction model. Combined with the deep level transient spectra results, this revealed that the concentrations of intrinsic defects in ZnO grains and the densities of interfacial states in ZnO/p-Si heterojunction varied with the different annealing ambiences, which caused the grain boundary barriers in ZnO/p-Si heterojunction to vary. This resulted in adjustment electrical properties ofZnO/p-Si heterojunction that may be suitable in various applications.展开更多
The paper reports the fabrication and characterization of a novel Au/PVP/ZnO/Si/Al semiconductor heterojunction(HJ) diode. Both inorganic n type ZnO and organic polyvinyl pyrrolidone(PVP) layers have grown by sol-...The paper reports the fabrication and characterization of a novel Au/PVP/ZnO/Si/Al semiconductor heterojunction(HJ) diode. Both inorganic n type ZnO and organic polyvinyl pyrrolidone(PVP) layers have grown by sol-gel spin-coating route at 2000 rpm. The front and back metallic contacts are thermally evaporated in a vacuum at pressure of 10^-6 Torr having a diameter of 1.5 mm and a thickness of 250 nm. The detailed analysis of the forward and reverse bias current-voltage characteristics has been provided. Consequently, many electronic parameters, such as ideality factor, rectification coefficient, carrier concentration, series resistance, are then extracted.Based upon our results a non-ideal diode behavior is revealed and ideality factor exceeds the unity(n 〉 4). A high rectifying(-4.6 × 10^4) device is demonstrated. According to Cheung-Cheung and Norde calculation models, the barrier height and series resitance are respectively of 0.57 eV and 30 kΩ. Ohmic and space charge limited current(SCLC) conduction mechanisms are demonstrated. Such devices will find applications as solar cell, photodiode and photoconductor.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.11404302)the Laser Fusion Research Center Funds for Young Talents(Grant No.RCFPD1-2017-9)
文摘A series of Zn_(1-x)Cd_xO thin films have been fabricated on sapphire by pulsed-laser deposition(PLD), successfully. To investigate the effect of Cd concentration on structural and optical properties of Zn_(1-x)Cd_xO films, x-ray diffraction(XRD),ultraviolet-visible spectroscopy(UV-vis), and x-ray photoelectron spectroscopy(XPS) are employed to characterize the films in detail. The XRD pattern indicates that the Zn_(1-x)Cd_xO thin films have high single-orientation of the c axis. The energy bandgap values of ZnCdO thin films decrease from 3.26 eV to 2.98 eV with the increasing Cd concentration(x)according to the(αhν)~2–hν curve. Furthermore, the band offsets of Zn_(1-x)Cd_xO/ZnO heterojunctions are determinated by XPS, indicating that a type-I alignment takes place at the interface and the value of band offset could be tuned by adjusting the Cd concentration.
文摘We report the fabrication and characterization of light-emitting diodes based on n-ZnO/p-GaN heterojunctions. The n-type ZnO epilayer is deposited by metalorganic chemical vapor deposition (MOCVD) on a MOCVD grown Mg-doped p-GaN layer to form a p-n heterojunction. During the etching process, the relation between the etching depth and the etching time is linear in a HF and NH4 CI solution of a certain ratio. The etching rates of the SiO2 and ZnO are well controlled,which are essential for device fabrication. The current-voltage relationship of this heterojunction shows a diode-like rectifying behavior. In contrast to previous reports,electroluminescence (EL) emissions are observed by the naked eye at room temperature from the n-ZnO/p-GaN heterojunction under forward-and reverse-bias. The origins of these EL emissions are discussed in comparison with the pho- toluminescence spectra.
基金Project supported by the National Natural Science Foundation of China(Grant No.11144010)the Research Award Fund for Outstanding Middle-aged Young Scientist of Shandong Province,China(Grant No.BS2011ZZ004)
文摘n-ZnO/p-GaN heterojunction light-emitting diodes with and without a Ga2O3 interlayer are fabricated. The electroluminescence (EL) spectrum of the n-ZnO/p-GaN displays a single blue emission at 430 nm originating from GaN, while the n-ZnO/Ga2O3/p-GaN exhibits a broad emission peak from ultraviolet to visible. The broadened EL spectra of n-ZnO/Ga2O3/p-GaN are probably ascribed to the radiative recombination in both the p-GaN and n-ZnO, due to the larger electron barrier (ΔEC=1.85 eV) at n-ZnO/Ga2O3 interface and the much smaller hole barrier (ΔEV=0.20 eV) at Ga2O3/p-GaN interface.
基金the Ministry of Higher Education High Impact Research (HIR F000032)the University of Malaya (RP022-2012A)for their generous financial support, and the Nanotechnology and Catalysis Research Centre (NANOCAT) for their analytical services
文摘Metal oxide semiconductor materials such as ZnO have tremendous potential as light absorbers for photocatalysed electrodes in the electrochemical reduction of water. Promoters such as rGO have been added to reduce the recombination losses of charge carriers and improve its photoelectrochemical activity. In this study, the effect of layer ordering on the charge transfer properties of rGO-hybridised ZnO sandwich thin films for the photo-catalysed electrochemical reduction of water was investigated. rGO-hybridised ZnO sandwich thin films were prepared via a facile electrode position technique using a layer-by-layer approach. The thin films were analysed using FESEM, XRD, Raman, PL, UV–vis, EIS and CV techniques to investigate its morphological, optical and electrochemical properties. The FESEM images show the formation of distinct layers of rGO and ZnO nanorods/flakes via the layer-by-layer method. XRD confirmed the wurtzite structure of ZnO. PL spectroscopy revealed a reduction of photoemission intensity in the visible region(580 nm) when rGO was incorporated into the ZnO thin film. Among the six thin films prepared, ZnO/rGO showed superior performance compared to the other thin films(0.964 m A/cm) due to the presence of graphene edges which participate as heterogenous electrocatalysts in the photocatalysed electrolysis of water. rGO also acts as electron acceptor, forming an n-p heterojunction which improves the activity of ZnO to oxidise water molecules to O2. EIS revealed that the application of rGO as back contact(rGO/ZnO, rGO/ZnO/rGO) reduces the charge transfer resistance of a semiconductor thin film. Alternatively, rGO as front contact(ZnO/rGO, rGO/ZnO/rGO) improves the photo-catalysed electrolysis of water through the participation of the rGO edges in the chemical activation of water. The findings from this study indicate that the layer ordering significantly affects the thin film's electrostatic properties and this understanding can be further advantageous for tunable applications.
基金Project supported by the National Natural Science Foundation of China(Nos.50472009,10474091,50532070)
文摘Heteroepitaxial undoped ZnO films were grown on Si (100) substrates by radio-frequency reactive sputtering, and then some of the samples were annealed at N2-800℃ (Sample 1, S1) and 02-800℃ (Sample 2, S2) for 1 h, respectively. The electrical transport characteristics of a ZnO/p-Si heterojunction were investigated. We found two interesting phenomena. First, the temperature coefficients of grain boundary resistances of S 1 were positive (positive temperature coefficients, PTC) while that of both the as-grown sample and S2 were negative (negative temperature coefficients, NTC). Second, the I-V properties of S2 were similar to those common p-n junctions while that of both the as-grown sample and S 1 had double Schottky barrier behaviors, which were in contradiction with the ideal p-n heterojunction model. Combined with the deep level transient spectra results, this revealed that the concentrations of intrinsic defects in ZnO grains and the densities of interfacial states in ZnO/p-Si heterojunction varied with the different annealing ambiences, which caused the grain boundary barriers in ZnO/p-Si heterojunction to vary. This resulted in adjustment electrical properties ofZnO/p-Si heterojunction that may be suitable in various applications.
基金supported by the Algerian Ministry of High Education and Scientific Research through the CNEPRU project No.B00L02UN310220130011,www.mesrs.dz,and www.univ-usto.dzincluded in ANVREDET PROJECT N° 18/DG/2016 “projet innovant:synthèse et caractérisation de films semiconducteurs nanostructurés et fabrication de cellule solaire” 2016,http://www.anvredet.org.dz
文摘The paper reports the fabrication and characterization of a novel Au/PVP/ZnO/Si/Al semiconductor heterojunction(HJ) diode. Both inorganic n type ZnO and organic polyvinyl pyrrolidone(PVP) layers have grown by sol-gel spin-coating route at 2000 rpm. The front and back metallic contacts are thermally evaporated in a vacuum at pressure of 10^-6 Torr having a diameter of 1.5 mm and a thickness of 250 nm. The detailed analysis of the forward and reverse bias current-voltage characteristics has been provided. Consequently, many electronic parameters, such as ideality factor, rectification coefficient, carrier concentration, series resistance, are then extracted.Based upon our results a non-ideal diode behavior is revealed and ideality factor exceeds the unity(n 〉 4). A high rectifying(-4.6 × 10^4) device is demonstrated. According to Cheung-Cheung and Norde calculation models, the barrier height and series resitance are respectively of 0.57 eV and 30 kΩ. Ohmic and space charge limited current(SCLC) conduction mechanisms are demonstrated. Such devices will find applications as solar cell, photodiode and photoconductor.