Generalized four-point characterization method for resistive and capacitive contacts

In this paper, a four-point characterization method is developed for resistive samples connected to either resistive or capacitive contacts. Provided the circuit equivalent of the complete measurement system is known including coaxial cable and connector capacitances as well as source output and amplifier input impedances, a frequency range and capacitive scaling factor can be determined, whereby four-point characterization can be performed. The technique is demonstrated with a discrete element test sample over a wide frequency range using lock-in measurement techniques from 1 Hz - 100 kHz. The data fit well with a circuit simulation of the entire measurement system. A high impedance preamplifier input stage gives best results, since lock-in input impedances may differ from manufacturer specifications. The analysis presented here establishes the utility of capacitive contacts for four-point characterizations at low frequency.Comment: 21 pages, 10 figure

Introduction to (p × n)-Type Transverse Thermoelectrics

This chapter will review (p × n)-type transverse thermoelectrics (TTE). Starting with the device advantages of single-leg (p × n)-type TTE’s over other thermoelectric paradigms, the theory of (p × n)-type TTE materials is given. Then, the figure of merit, transport equations, and thermoelectric tensors are derived for an anisotropic effective-mass model in bulk three-dimensional materials (3D), quasi-two-dimensional (2D), and quasi-one-dimensional (1D) materials. This chapter concludes with a discussion of the cooling power for transverse thermoelectrics in terms of universal heat flux and electric field scales. The importance of anisotropic ambipolar conductivity for (p × n)-type TTEs highlights the need to explore noncubic, narrow-gap semiconductor or semimetallic candidate materials

Advances in Growth, Doping, and Devices and Applications of Zinc Oxide

Zinc oxide is a breakthrough multifunctional material of emerging interest applicable in the areas of electronics, computing, energy harvesting, sensing, optoelectronics, and biomedicine. Zno has a direct and wide bandgap and high exciton binding energy. It is nontoxic, earth-abundant, and biocompatible. However, the growth and characterization of high-quality zno has been a challenge and bottleneck in its development. Efforts have been made to synthesize device-quality zinc oxide and unleash its potential for multiple advanced applications. Zno could be grown as thin films, nanostructures, or bulk, and its properties could be optimized by tuning the growth techniques, conditions, and doping. Zinc oxide could be a suitable material for next generation devices including spintronics, sensors, solar cells, light-emitting diodes, thermoelectrics, etc. It is important and urgent to collate recent advances in this material, which would strategically help in further research and developments in zno. This paper provides a coherent review of developments in zno growth, leading to its advancing applications. Recent developments in growth technologies that address native defects, current challenges in zinc oxide, and its emerging applications are reviewed and discussed in this article

XPS characterization of Al\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e3\u3c/sub\u3e/ZnO ultrathin films grown by atomic layer deposition

© 2020 Author(s). The near-surface compositional properties of double-layer Al2O3/ZnO ultrathin films, grown on the n-type GaAs substrate using the atomic layer deposition (ALD) technique, are analyzed by means of high-resolution x-ray photoelectron spectroscopy (XPS). This structure has been used as the dielectric or the passivation layer in microelectronic devices, such as metal-oxide-semiconductor (MOS) capacitors, field-effect transistors, and Schottky junctions. The XPS spectra of double-layer Al2O3/ZnO thin films were obtained using monochromatic Al kα monochromatic radiation at 1486.6 eV and included an overall survey scan, in addition to the high-resolution spectra of Zn 2p, Al 2p, O 1s, Ga 2p, and As 3d

Four-point characterization using capacitive and ohmic contacts

A four-point characterization method is developed for semiconductor samples that have either capacitive or ohmic contacts. When capacitive contacts are used, capacitive current- and voltage-dividers result in a capacitive scaling factor which is not present in four-point measurements with only ohmic contacts. Both lock-in amplifier and pre-amplifier are used to measure low-noise response over a wide frequency range from 1 Hz -- 100 kHz. From a circuit equivalent of the complete measurement system after carefully being modeled, both the measurement frequency band and capacitive scaling factor can be determined for various four-point characterization configurations. This technique is first demonstrated with a discrete element four-point test device and then with a capacitively and ohmically contacted Hall bar sample using lock-in measurement techniques. In all cases, data fit well to a circuit simulation of the entire measurement system over the whole frequency range of interest, and best results are achieved with large area capacitive contacts and a high input-impedance preamplifier stage. Results of samples (substrates grown by Max Bichler Dieter Schuh, and Frank Fischer of the WSI) measured in the QHE regime in magnetic fields up to 15 T at temperatures down to 1.5 K will also be shown

PEDOT:PSS/n-Si Hybrid Solar Cells with Al₂O₃ Interfiacial Passivation Layer

Hybrid solar cells, consisting of both organic and inorganic layers have shown to be promising in developing solar cells with suitable photovoltaic properties, advantage of low temperature processing and much lower production cost than conventional p-n junction solar cells. For example, poly (3,4-ethylene-diozythiophene): polystyrenesulfonate (PEDOT:PSS) with work function of 5.1 eV and spin-coated on Si substrate leads to development of a rectifying Schottky junction and is used to design and fabricate hybrid solar cells, in which the organic PEDOT:PSS acts as a hole transporting layer. It has been shown in that the organic layer in a PEDOT:PSS/ n-Si hybrid solar cell, fabricated at temperatures below 100 C°, can also act as electron blocking layer, resulting in a low reverse saturation current density of 3.8 x 10-9 mA/cm2 and Schottky barrier height of 0.8 eV. Furthermore, Aluminum oxide (Al2O3) is shown to be effective as the passivation layer in improving the photovoltaic properties of solar cells by passivating the dangling bonds and reducing the density of surface states

Fabrication and Verification of a Glass-Silicon-Glass Micro-/Nanofluidic Model for Investigating Multi-Phase Flow in Shale-Like Unconventional Dual-Porosity Tight Porous Media

Unconventional shale or tight oil/gas reservoirs that have micro-/nano-sized dual-scale matrix pore throats with micro-fractures may result in different fluid flow mechanisms compared with conventional oil/gas reservoirs. Microfluidic models, as a potential powerful tool, have been used for decades for investigating fluid flow at the pore-scale in the energy field. However, almost all microfluidic models were fabricated by using etching methods and very few had dual-scale micro-/nanofluidic channels. Herein, we developed a lab-based, quick-processing and cost-effective fabrication method using a lift-off process combined with the anodic bonding method, which avoids the use of any etching methods. A dual-porosity matrix/micro-fracture pattern, which can mimic the topology of shale with random irregular grain shapes, was designed with the Voronoi algorithm. The pore channel width range is 3 µm to 10 µm for matrices and 100-200 µm for micro-fractures. Silicon is used as the material evaporated and deposited onto a glass wafer and then bonded with another glass wafer. The channel depth is the same (250 nm) as the deposited silicon thickness. By using an advanced confocal laser scanning microscopy (CLSM) system, we directly visualized the pore level flow within micro/nano dual-scale channels with fluorescent-dyed water and oil phases. We found a serious fingering phenomenon when water displaced oil in the conduits even if water has higher viscosity and the residual oil was distributed as different forms in the matrices, micro-fractures and conduits. We demonstrated that different matrix/micro-fracture/macro-fracture geometries would cause different flow patterns that affect the oil recovery consequently. Taking advantage of such a micro/nano dual-scale \u27shale-like\u27 microfluidic model fabricated by a much simpler and lower-cost method, studies on complex fluid flow behavior within shale or other tight heterogeneous porous media would be significantly beneficial