Hall Mobility Research Articles

Investigation of the Electronic Properties of Silicon Carbide Films with Varied Si/C Ratios Annealed at Different Temperatures

Hydrogenated amorphous SiC (a-SiC:H) films with various Si/C ratios were prepared using the plasma-enhanced chemical vapor deposition (PECVD) technique. These films were then subjected to thermal annealing at different temperatures to induce crystallization. The electronic properties of the annealed SiC films were investigated through temperature-dependent Hall mobility measurements. It was found that the room-temperature Hall mobilities in the SiC films increased with both the annealing temperature and the Si/C ratio. This increase was attributed to the improved crystallization in the SiC films. Importantly, SiC films with different Si/C ratios annealed at different temperatures exhibited varying temperature dependence behaviors in their Hall mobilities. To understand this behavior, a detailed investigation of the transport processes in SiC films was carried out, with a particular emphasis on the grain boundary scattering mechanisms.

Al 0.3 Ga 0.7 N/GaN HEMT Yapısı için QMSA Metodu Uygulanması

In this study, Al 0.3 Ga 0.7 N/GaN high electron mobility transistor (HEMT) structure is grown on a sapphire (Al2O3) substrate by using metal-organic vapor phase epitaxy (MOVPE), and its electron transport and magnetic transport properties are investigated. Resistivity is measured in the 20-350 K temperature range. Hall mobility and Hall carrier concentration are measured in the 0-1.5 T magnetic field range and the same temperature range. Magnetic transport properties are analyzed using quantitative mobility spectrum analysis (QMSA). 2DEG and 3DEG transport mechanisms are separated by using QMSA results.

Effect of oxygen flow on electrical and optical properties of ITO films synthesized by magnetron sputtering method

The tin-doped indium oxide thin films were synthesized by DC magnetron sputtering on the surface of polished silicon samples and glass slides in a mixed argon-oxygen atmosphere. The other deposition parameters: operating pressure, magnetron power and substrate rotation speed were kept constant. Thickness and density of thin films were measured by X-ray Reflectometry. The effects of oxygen flow rate and substrate temperature on the optical and electrical properties were investigated. The electrical properties (resistivity, Hall mobility and charge concentration) of the thin films were measured by the Van der Pauw method using the Hall effect. The minimum value of resistivity 0.52 × 10-3 Ohm·cm, and maximum charge mobility 28 cm2V-1s-1 was achieved at an oxygen proportional gas mixture of 2.6% (0.71 sccm). The transmission spectra of the films were measured in the wavelength range from 300 to 1100 nm. The transmittance of all films exceeds 75% in the visible and near-infrared spectral ranges. It was found that increasing the oxygen flow rate and heating of the substrate up to optimal value 150°C led to an increase in the crystallinity of the films and, consequently, to an increase in the Hall mobility and the transmittance.

The Study of the Electrical Properties of Anisotropic Semiconductors in the Laboratory Workshop of the University Course in Physics

The purpose of the article is to develop a theoretically and experimentally substantiated specific laboratory work for studying the anisotropy of the electrical properties of semiconductors within the framework of the curricula of higher educational institutions, for such areas of training as “Physics”, “Technical Physics”, “Radiophysics” and “Electronics and Nanoelectronics”. The relevance of the problem is due to the desire of domestic electronics for technological sovereignty and high requirements for the training of qualified personnel for the production of structures of solid-state functional electronics. Based on the solution of the boundary electrodynamic problem, an expression is obtained for the electric potential in the region of a thin rectangular semiconductor sample with a tensor character of conductivity. The results of this work is the development of an original laboratory setup for the demonstration and practical study of the anisotropy of the electrical properties of semiconductor crystals. The proposed technique makes it possible to determine the main electrokinetic parameters of an anisotropic semiconductor – specific conductivity, concentration and Hall mobility of the main charge carriers. A schematic diagram of the installation and formulas for calculating the errors of the measured quantities are proposed. The results obtained may also be of scientific interest in the study of anisotropic semiconductor materials in laboratory conditions.

Unraveling the limiting factors to electron mobility in degenerately doped SnO2 thin films

This paper presents a comprehensive theoretical study on electron mobility in highly doped polycrystalline SnO2 thin films, a widely employed material in modern devices. Our physical model incorporates phonon-electron interaction, ionised impurity, and grain boundaries as scattering mechanisms, effectively explaining the temperature and electron density-dependent variation of electron mobility in doped polycrystalline SnO2 thin films. We highlight the significant influence of trap density at grain boundaries, the self-compensation effect, and average grain size on the theoretical limit of electron mobility. At a doping level of 1019 cm−3, the limit is estimated at 100 cm2.V−1.s−1, while for 1020 cm−3, it reduces to 50 cm2.V−1.s−1. These factors are strongly influenced by deposition conditions, including temperature, precursor chemistry, and deposition atmosphere. By analysing Hall mobility with respect to carrier density, temperature, or film thickness using our model, a better understanding of the limiting mechanisms in electron mobility can be achieved. This knowledge can guide the development of appropriate experimental strategies to enhance electron mobility in highly doped polycrystalline SnO2 films for advancing the performance of SnO2-based devices across various applications.

Swift heavy ion irradiation induced modifications on the structure, optical and electrical properties of pulsed laser deposited anatase TiO2 thin films

The swift heavy ions of Ag7+ (100 MeV) were used to irradiate the anatase TiO2 thin films prepared by pulsed laser deposition (PLD) technique on quartz substrates. The effect of ion fluences (1×1012, 1×1013 and 1×1014 ions/cm2) on the structure, surface morphology, optical and electrical properties are investigated through several analytical techniques such as XRD, Micro-Raman, FTIR, XPS, AFM, FESEM, UV–visible and Hall measurements. The analysis of XRD data shows a gradual shift in the (101) plane toward higher diffraction angle on increasing the ion fluence which increases the lattice strain in the films. The EDS spectra reveal a modest Ti-rich composition with a significant shift following irradiation for both as-grown and irradiated films. The development of hillocks at increased ion fluence and considerable grain splitting following irradiation are observed in SEM micrographs. AFM images exhibit increase in surface roughness with the increase in ion fluence. Moreover, there is a significant drop in the band gap of the irradiated thin films from 3.92 to 3.44 eV with the increase in ion fluence. The various electrical parameters such as carrier concentrations (n), Hall mobility (μ), electrical resistivity (ρ), Hall coefficient (RH), etc., are determined by the Hall measurements at room temperature. This study indicates that the SHI irradiation plays a significant role in tunning the physical properties of anatase TiO2 thin films.

AlGaN High Electron Mobility Transistor for High Temperature Logic

We report on AlGaN HEMT-based logic development, using combined enhancement- and depletion-mode transistors to fabricate inverters with operation from room temperature up to 500°C. Our development approach included: (a) characterizing temperature dependent carrier transport for different AlGaN HEMT heterostructures, (b) developing a suitable gate metal scheme for use in high temperatures, and (c) over-temperature testing of discrete devices and inverters. Hall mobility data revealed the GaN-channel HEMT experienced a 6.9× reduction in mobility, whereas the AlGaN channel HEMTs experienced about a 3.1x reduction. Furthermore, a greater aluminum contrast between the barrier and channel enabled higher carrier densities in the two-dimensional electron gas for all temperatures. The combination of reduced variation in mobility with temperature and high sheet carrier concentration showed that an Al-rich AlGaN-channel HEMT with a high barrier-to-channel aluminum contrast is the best option for an extreme temperature HEMT design. Three gate metal stacks were selected for low resistivity, high melting point, low thermal expansion coefficient, and high expected barrier height. The impact of thermal cycling was examined through electrical characterization of samples measured before and after rapid thermal anneal. The 200 nm tungsten gate metallization was the top performer with minimal reduction in drain current, a slightly positive threshold voltage shift, and about an order of magnitude advantage over the other gates in on-to-off current ratio. After incorporating the tungsten gate metal stack in device fabrication, characterization of transistors and inverters from room temperature up to 500°C was performed. The enhancement-mode (e-mode) devices’ resistance started increasing at about 200°C, resulting in drain current degradation. This phenomenon was not observed in depletion-mode (d-mode) devices but highlights a challenge for inverters in an e-mode driver and d-mode load configuration.

Effect of addition of indium oxide layer on all-inorganic perovskite solar cells

In perovskite solar cells, the interface plays a crucial role in photovoltaic performance because excitons dissociate and compound at the interface. In this paper, the optical absorption layer of In2O3 planar perovskite solar cells is studied, which is an efficient intermediate layer between the TiO2 electron transport layer and perovskite. The modification of the In2O3 interlayer increases the average power conversion efficiency from 6.74% to 10.68%. Based on this background, some other feature descriptions are also carried out. The results show that the photovoltaic performance can be improved by depositing the In2O3 interlayer, mainly due to the improved film morphology, reduced recombination center, bulk carrier concentration and Hall mobility. It has been shown that In2O3 can be used as an efficient interface material on all-inorganic perovskite solar cells.

Impact of Grain Size and Grain Nature in Thin‐Film Solar Cells

Herein, a theoretical investigation is conducted on grain‐size inhomogeneity's impact and grain boundaries’ (GBs’) electrical nature in thin‐film solar cells. Using the Matthiessen rule, grain‐size‐dependent mobility is derived in polycrystalline material. The obtained grain‐size‐dependent mobility values are fed into the Poisson solver to calculate device performance. The severity of grain sizes in the lower region determines how grain size affects the photovoltaic performance by grain‐size‐dependent efficiency simulation. Low grain sizes become critical, especially for low‐thickness absorbers. The second aspect of the study assesses potential variation at GBs to reveal the impact of the electrical properties of GBs. Evidence shows that the acceptor defects at GB are benign for device performance, causing upward band bending at the GB and acting as electron barriers. Device performance is adversely affected by donor defects at GBs due to downward band bending. As summarized in the findings, the polycrystallinity‐induced cause–effect relationships of grains are likely to interest solar cell researchers.

Optimizing Thermoelectric Performance of Tellurium via Doping with Antimony and Selenium.

Forming solid solutions is one of the most effective strategies to suppress the thermal conductivity of thermoelectric materials. However, the accompanying increase in impurity ion scattering usually results in an undesirable loss in hall mobility, negatively impacting the electrical transport properties. In this work, a tellurium-selenium (Te-Se) solid solution with trace antimony (Sb) doping was synthesized via the high pressure and high temperature method. It was found that slight Se doping into the Te sites not only had no impact on the hall mobility and carrier concentration, but also enhanced the density-of-state effective mass of Sb0.003Te0.997, leading to an enhanced power factor near room temperature. Additionally, the presence of Se doping caused a significant reduction in the phonon thermal conductivity of Te due to fluctuations in the mass and strain field. The lowest phonon thermal conductivity was as low as ~0.42 Wm-1K-1 at 600 K for Sb0.003Se0.025Te0.972, which approached the theoretical minimum value of Te (~0.28 Wm-1K-1). The effects of Se doping suppressed thermal conductivity, while Sb doping enhanced the power factor, resulting in a larger ZT of ~0.94 at 600 K. Moreover, these findings demonstrate that Sb and Se doping can effectively modulate the electrical and thermal transport properties of Te in a synergistic manner, leading to a significant increase in the average ZT across a wide temperature range.

Influence of processing conditions on the titanium/nickel contact metallization on a silicon wafer for thermal management

Thermal management of both digital and power electronics is becoming challenging with device miniaturization and a need for delivering higher power. Diamond thin films and substrates are attractive for thermal management applications in power electronics because of their high thermal conductivity. However, deposition of diamond by microwave plasma enhanced chemical vapor deposition requires high temperatures, which can degrade metallization used in power electronic devices. In this research, Titanium (Ti)- Nickel (Ni) thin films are deposited by direct current magnetron sputtering on p-type Silicon (Si) (100) substrates using a physical mask for creating dot-patterns for measuring properties of the contact metallization. The influence of processing conditions and post-deposition annealing in Argon and hydrogen at 380 °C for 1 h on the properties of the contact metallization are studied by measuring the current - voltage characteristics and Hall effect. The results indicated ohmic contact resistance for both, the as-deposited films and after post annealing treatments. In addition, the results on contact resistance, resistivity, carrier concentration and hall mobility of wafers extracted from Ti/Ni metal contact to p-type Si (100) are presented and discussed.

Impact of air exposure on growth rate and electrical properties of SnO2 thin films by atmospheric pressure spatial atomic layer deposition

SnO2 thin film is one of the most studied transparent conductive materials that can be deposited using vacuum-free techniques such as atmospheric pressure spatial atomic layer deposition (AP-SALD). This work studies SnO2 thin films prepared from tin(II) acetylacetonate and water vapor, with a particular focus on the impact of air exposure during the AP-SALD process on the growth rate and electrical properties of the films. In-situ resistance measurements and ex-situ Hall effect characterization demonstrated that longer exposure time of the growing film surface to the open air (t air) at 240 °C led to conductivity degradation, while the film thickness decreases. The theoretical calculations show that −OH and (oxygen molecule adsorbed on the five-coordinated Sn atom, also called O2 dimer) are the two most stable surface structures. The formation of is shown as the most thermodynamically favorable oxygen-related species on SnO2(110) surface formed when the film is exposed to the open air, giving rise to both the decrease of film thickness (associated with the desorption of −OH surface groups) and the increase of film resistivity versus t air. The optimized polycrystalline SnO2 sample demonstrated relatively good electrical performance, including an electrical resistivity of 9.3 × 10−3 Ω.cm, carrier density of 9.2 × 1019 cm−3, and Hall mobility of 7.3 cm2 V−1 s−1 at a growth temperature as low as 240 °C. Our findings reveal the critical impact of processing in the open air on the electrical conductivity of the obtained SnO2 films by AP-SALD coating technology.

Enhanced electrodynamic characteristic and tunable band gap formed by the multilayer TixZn oxide film promising as a photoanode for solar cells

As a clean and efficient energy material, the efficiency of solar battery can be greatly promoted by matching suitable photoanode. Among them, TiO2 and ZnO are natural materials with appropriate energy level and excellent carrier concentration, which have enormous application potential. Herein, a multilayer Ti10Zn oxide film with similar band gap of TiO2 (ECB=−0.70 V vs. NHE) and a parallel electrical property of ZnO has been obtained by atomic layer deposition (ALD). The formation mechanism has been analyzed by comparing multilayer TixZn oxide films with different proportions and pure TiO2 (ZnO) film. Firstly, scanning electron microscope (SEM) indicating homogeneous morphology of these films. Then X-ray photoelectron spectroscopy (XPS) along with the X-ray diffraction (XRD) measurements and the thicknesses fitted by ellipsometric spectra reveal that when x > 10, the ZnO substance mainly exist in the form of interstitial atoms and conversely occupies a separate layer of spatial structure when x < 10. While the film shows maximum Zn 2p3/2 binding energy and preferential growth orientation of spacing in (002) direction with ZnO-like crystal structure when x = 10 (Ti10Zn). The resistivity and Hall measurement confirm Ti10Zn with an excellent electrodynamic property with a parallel Hall mobility of 9.34 cm2 and carrier density of 1.86 × 1020 cm−3 even higher than that of pure ZnO. Transmission spectra along with photo-luminescence measurement demonstrated similar band gap values of TixZn oxide films with TiO2 and high spectral transmittance (solar light utilization rate>70%). This work highlights TiO2/ZnO composite films with great application prospects as solar cell photoanode materials and other optoelectronic application fields.

The Dominant Effects of Hopping Conduction on the Seebeck Coefficient and the Hall Mobility in p-Type CuInTe2 and CuGaTe2

The Dominant Effects of Hopping Conduction on the Seebeck Coefficient and the Hall Mobility in p-Type CuInTe2 and CuGaTe2

Controllable Chemical Vapor Deposition Growth of High-Mobility Bi2O2Te Nanosheets.

Air-stable bismuth oxychalcogenides (Bi2O2X) have exhibited exceptional electrical properties and ultrahigh mobility in high-performance electronic devices. However, although Bi2O2Se is commonly used, there have been few reported uses of Bi2O2Te because of its challenging preparation process. This study aimed to synthesize two-dimensional Bi2O2Te nanosheets using the chemical vapor deposition method. Bi2O2Te nanosheets with different thicknesses were obtained by adjusting the growth conditions, such as temperature. The as-prepared Bi2O2Te single crystal exhibited a Hall mobility of 496 cm2 V-1 s-1 at 300 K, which reached 5000 cm2 V-1 s-1 at 2 K. The results expand the Bi2O2X family and show Bi2O2Te to be a promising candidate for use in highly efficient electronic devices.

Large-area epitaxial growth of InAs nanowires and thin films on hexagonal boron nitride by metal organic chemical vapor deposition

Large-area epitaxial growth of III–V nanowires and thin films on van der Waals substrates is key to developing flexible optoelectronic devices. In our study, large-area InAs nanowires and planar structures are grown on hexagonal boron nitride templates using metal organic chemical vapor deposition method without any catalyst or pre-treatments. The effect of basic growth parameters on nanowire yield and thin film morphology is investigated. Under optimised growth conditions, a high nanowire density of 2.1 109 cm−2 is achieved. A novel growth strategy to achieve uniform InAs thin film on h-BN/SiO2/Si substrate is introduced. The approach involves controlling the growth process to suppress the nucleation and growth of InAs nanowires, while promoting the radial growth of nano-islands formed on the h-BN surface. A uniform polycrystalline InAs thin film is thus obtained over a large area with a dominant zinc-blende phase. The film exhibits near-band-edge emission at room temperature and a relatively high Hall mobility of 399 cm−2/(Vs). This work suggests a promising path for the direct growth of large-area, low-temperature III–V thin films on van der Waals substrates.

Highly Conductive Covalent-Organic Framework Films.

Chemically inert organic networks exhibiting electrical conductivity comparable to metals can advance organic electronics, catalysis, and energy storage systems. Covalent-organic frameworks (COFs) have emerged as promising materials for those applications due to their high crystallinity, porosity, and tunable functionality. However, their low conductivity has limited their practical utilization. In this study, copper-coordinated-fluorinated-phthalocyanine and 2,3,6,7-tetrahydroxy-9,10-anthraquinone-based COF (CuPc-AQ-COF) films with ultrahigh conductivity are developed. The COF films exhibit an electrical conductivity of 1.53 × 103 S m-1 and a Hall mobility of 6.02 × 102 cm2 V-1 s-1 at 298K, reaching the level of metals. The films are constructed by linking phthalocyanines and anthraquinones through vapor-assisted synthesis. The high conductivity properties of the films are attributed to the molecular design of the CuPc-AQ-COFs and the generation of high-quality crystals via the vapor-assisted method. Density functional theory analysis reveals that an efficient donor-acceptor system between the copper-coordinated phthalocyanines and anthraquinones significantly promotes charge transfer. Overall, the CuPc-AQ-COF films set new records of COF conductivity and mobility and represent a significant step forward in the development of COFs for electronic, catalytic, and electrochemical applications.

High-concentration F-incorporated ZnO thin films doped via femtosecond-laser hyperdoping

ZnO is a transparent conductive oxide that has received great attention over the past few decades, as it is a key component in light-emitting diodes, gas sensors, and solar cells. However, the electrical conductivity of intrinsic ZnO is not ideal, and thus, ZnO is often doped with appropriate elements such as fluorine (F). Unfortunately, the lack of adequate precursors in traditional doping methods may increase the difficulty of ZnO doping with F. In this work, we realized, for the first time, high-concentration F-doped ZnO thin films with a high Hall mobility of 20.7 cm2/V/s via femtosecond-laser hyperdoping. The highest atomic percentage of F was determined to be 8.3 at.%, which was over three times larger than that of previously reported F-doped ZnO films. Compared with pristine ZnO, the highest carrier concentration of the F-doped ZnO could be increased by four orders of magnitude, and the resistivity could be reduced by three orders of magnitude. Our results demonstrated that the femtosecond-laser hyperdoping technology could achieve efficient non-metallic hyperdoping of ZnO with high transparency and Hall mobility, thereby reducing the power dissipation and improving the current carrying capacity of ZnO-based devices.

High mobility hydrogen-terminated diamond FET with h-BN gate dielectric using pickup method

Hydrogen-terminated diamond surfaces, emerging as a promising two-dimensional (2D) electron platform with great thermal and electronic properties, hold great potential for the next-generation high power and high frequency field effect transistor (FET). However, ideal gate dielectrics with high crystallinity and defect-free surfaces are still largely elusive. In this work, using the contamination-free pickup transfer method, hexagonal boron nitride (h-BN) flakes were fabricated on top of the hydrogen-terminated diamond surface to serve as a gate material and the passivation layer. The morphological and optical characterizations revealed the formation of homogeneous and intimate interface between h-BN and diamond. Benefiting from the h-BN gate dielectric layer, the maximum drain current density, subthreshold swing, and on/off ratio of diamond FET are measured to be −210.3 mA mm−1, 161 mV/dec, and 106, respectively. Especially, the transport measurement shows an almost constant Hall mobility of around 260 cm2 V−1 s−1 in the hole density range of 2 − 6 × 1012 cm−2, suggesting the excellent gate controllability of h-BN. Our results indicate that h-BN could form high-quality interface with hydrogen-terminated diamond, paving the way for the development of diamond-based electronic applications.

The electronic properties of boron-doped germanium nanocrystals films

Various doping concentrations of boron (B)-doped germanium nanocrystal (Ge NC) films were prepared using the plasma-enhanced chemical vapor deposition (PECVD) technique followed by thermal annealing treatment. The electronic properties of B-doped Ge NCs films combined with the microstructural characterization were investigated. It is worthwhile mentioning that the Hall mobilities {mu }_{mathrm{Hall}} of Ge NCs films were enhanced after B doping and reached to the maximum of 200 cm2 V−1, which could be ascribed to the reduction in surface defects states in the B-doped films. It is also important to highlight that the temperature-dependent mobilities {mu }_{mathrm{H}}(T) exhibited different temperature dependence trends in the Ge NCs films before and after B doping. A comprehensive investigation was conducted to examine the distinct carrier transport properties in B-doped Ge NC films, and a detailed discussion was presented, focusing on the scattering mechanisms involved in the transport process.