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Variable-range-hopping conduction and polaron dielectric relaxation in Cu and Nb co-doped BaTiO3
摘要： BaTi0.7(Cu0.1Nb0.2)O3 ceramic was prepared using a solid-state method and its structure, valence states, conduction mechanism and dielectric properties were investigated in detail. A fine-grained microstructure and a distorted pseudo-cubic perovskite structure were confirmed by scanning electron microscopy, X-ray diffraction analysis and Raman spectroscopy. X-ray photoelectron spectroscopy analysis suggested that Cu in BaTi0.7(Cu0.1Nb0.2)O3 was polyvalent but the valence states of Ti and Nb were invariable. Mott’s variable-range-hopping (VRH) conduction was observed. The two colossal dielectric constant plateaus in low- and high-temperature ranges were ascribed to the electrode and grain boundary responses, respectively. The VRH model described the low-temperature relaxation well, indicating that the dielectric relaxation was a polaron relaxation rather than Maxwell–Wagner type. Both grain and grain boundary resistances were well fitted by the VRH model, suggesting that the VRH mechanism was tenable in both grain and grain boundaries. The electron paramagnetic resonance signal was ascribed to Cu ions, and the linewidth showed a linear relationship with T?1/4, corresponding to the charge transfer between different valence via Cu+-O-Cu2+ and Cu2+-O-Cu3+ paths. The hopping of carriers was also responsible for the conduction and polaron dielectric relaxations.
关键词： Variable-range-hopping conduction,Electron paramagnetic resonance.,Dielectric relaxation,Cu and Nb co-doped BaTiO3
更新于2025-09-23 15:23:52
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Temperature Dependent Electrical Transport Properties of High Carrier Mobility Reduced Graphene Oxide Thin Film Devices
摘要： We confirm variable electrical transport properties of high mobility reduced graphene oxide (RGO) thin films fabricated by pulse laser deposition. The temperature dependent (5K–350K) four terminal electrical transport property measurements range hopping and thermally activated transport mechanism of the charge carriers at low (5K–210K) and high temperature (210K–350K) regions, respectively. The calculated localization length, the density of states near the Fermi level (EF), hopping energy, and Arrhenius energy gap provide useful information to explain the excellent electrical properties of the RGO films. Hall mobility measurement confirms p-type characteristics of the thin films. The charge carrier Hall mobility can be engineered by tuning the growth parameters, and the measured maximum mobility was 1596 cm2v-1s-1. The optimization of the improved electrical property is well supported by structural properties such as the defect density, average size of sp2 clusters and degree of reduction, which were investigated by Raman spectroscopy and X-ray diffraction analysis.
关键词： PLD,variable range hopping,and Raman spectroscopy,hall mobility,Reduced graphene oxide,localization length
更新于2025-09-23 15:22:29
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Reduced Graphene Oxide-Nanostructured Silicon Photosensors With High Photoresponsivity at Room Temperature
摘要： We have created nanostructured Si (~3 nm) with a direct band gap of 1.37 eV on electrically conducting reduced graphene oxide (rGO) for a highly efficient photosensor. This robust photosensor is fabricated using a non-equilibrium processing route, where nanosecond excimer laser pulses melt the alternating layers of Si and amorphous carbon to form micropillars and nanoreceptors of Si on rGO layers. The incident white light generates free carriers in the Si microstructures and nanoreceptors which are ballistically transported (via rGO layers) to the external circuit under the application of a voltage bias. The responsivity of rGO-Si devices to light (resistance vs time) and I-V measurements indicate an exponential drop in resistance with the incidence of white light and non-rectifying nature, respectively. Photoresponsivity of the rGO-Si devices is calculated to be 3.55 A/W at room temperature, which is significantly larger than the previously fabricated graphene-based Ohmic photosensors. Temperature-dependent resistance measurements of rGO-Si structures follow Efros-Shklovoskii variable range hopping (ES-VRH) electrical conduction in the low-temperature region (<100 K) and Arrhenius conduction in the high-temperature region (>100 K). In rGO, the localization length, hopping energy, and activation energy are calculated to be 17.58 μm, 3.15 meV, and 1.67 meV, respectively. The 2D nature of highly reduced and less defective rGO also render an interesting negative magnetoresistance (~2.5 %) at 5 K, thereby indicating potential implications of rGO-Si in opto-spintronics. The large-area integration of rGO-Si structures with sapphire employing nanosecond pulsed laser annealing and its exciting photosensing properties will open a new frontier for further extensive research in these functionalized 2D materials.
关键词： Pulsed laser annealing,Raman spectroscopy,Variable range hopping,Nanostructures,Reduced graphene oxide
更新于2025-09-23 15:22:29
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Electrical Transport Properties of Thin Film Composed of a-ZnO Nanorods
摘要： Background: Due to its wide band gap, high exciton binding energy and high breakdown strength, the nanostructures of ZnO may find applications for electronic, photonic devices, and high-frequency applications. Objective: The aim of the present work is to study electrical transport of thin film composed of a-ZnO nanorods. Method: Physical vapour condensation method was employed to fabricate the nanorods of ZnO. The morphology of these nanorods was investigated with the help of scanning electron microscope. X-ray diffraction pattern of as-prepared thin film was recorded using X-ray diffractometer. For dc conductivity measurements, four-probe method was used. Result: The as-prepared ZnO nanorods have diameter ranging from 10-20 nm and the length is of order of few hundred nanometers. XRD pattern of film composed of ZnO nanorods suggests the amorphous nature. Temperature dependence of dc conductivity has been studied over the temperature range of (297- 4.2K). For the temperature range of 297-120K, Mott’s three dimensional variable range hopping (VRH) is applied to explain the electrical conduction. For lower temperature range (120 - 4.2K), 2D-variable-range hopping in localized states near the Fermi level may be responsible for the transport of carriers. Conclusion: Variable range hopping mechanism (VRH) has been suggested for the entire temperature range (298-4.2K) on the basis of temperature dependence of dc conductivity data, which changes from 3D to 2D on moving to lower temperatures side (below 125K).
关键词： physical vapour condensation technique,variable range hopping,XRD,ZnO nanorods,SEM,Mott’s parameters,electrical conduction mechanism
更新于2025-09-23 15:22:29
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Sub-50 picosecond to microsecond carrier transport dynamics in pentacene thin films
摘要： Carrier transport dynamics from sub-50 ps to (cid:2)ls over five temporal decades in pentacene films was studied by transient photoconductivity. The behavior of the temperature independent photocurrent peak suggests that the photogenerated carriers exhibit pre-trapping transport in extended states upon pulsed laser excitation. From 300 ps to (cid:2)30 ns, the carriers thermalize and fall into shallow band tail states, and multiple-trapping and release transport dominates. From (cid:2)30 ns to (cid:2)ls, the weak temperature dependence of power-law photocurrent decay and the linear relation of logarithmic photocurrent with T(cid:3)1/4 suggest a variable range hopping transport in deep trap states.
关键词： transient photoconductivity,carrier transport dynamics,pentacene thin films,multiple-trapping and release transport,variable range hopping transport
更新于2025-09-23 15:21:21
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Improved Reverse Leakage Current in GaInN-based LEDs with a Sputtered AlN Buffer Layer
摘要： In this study, the improvement of reverse leakage current characteristics with a sputtered (SP) -AlN buffer layer in GaInN-based green light-emitting diodes (LEDs) has been presented for the first time. To understand the origin of the improvement, a detailed review and careful analysis of reverse leakage current characteristics were performed. The review and analysis identified that the improvement was primarily caused by the suppression of variable-range-hopping process obtained by replacing conventional low-temperature GaN buffer. Verification that threading dislocations and V- defects can enhance the variable-range-hopping process has been received. We believe that this study will contribute to the realization of green LEDs with advantages of high reliability, a long lifetime, and electrical robustness.
关键词： reverse leakage current,dot-like local emission,light-emitting diodes,Frenkel-Poole emission,variable-range-hopping
更新于2025-09-11 14:15:04