Hall Mobility Research Articles

High-Temperature Stable Amorphous Sn-Rich InSnGaO Thin Films Fabricated Via Atomic Layer Deposition for Next-Generation Dynamic Random-Access Memory Applications.

Facile phase transitions and electrical degradation of amorphous oxide semiconductors due to a high thermal budget have significantly limited their dynamic random-access memory (DRAM) applications, which require high thermal stability at temperatures over 600 °C. In this paper, we report an amorphous In-Sn-Ga-O (ITGO) semiconductor fabricated via atomic layer deposition, which exhibits high-temperature (∼700 °C) phase stability with moderate electrical properties. The optimal Sn-rich ITGO composition (In/Sn/Ga = 25:58:17 at. %) represents a thermally stable amorphous phase with excellent Hall mobility (24.0 cm2/(V s)) above 600 °C. Various analytical and simulation methods reveal the role of Sn as an efficient amorphous stabilizer and enhancer of electron mobility in oxide semiconductors. A thin-film transistor with a 4.5 nm-thick ITGO channel demonstrates excellent field-effect mobility (7.7 cm2/(V s)) and reliability. Therefore, Sn-rich ITGO is a promising candidate for next-generation DRAM channels that require amorphous-phase stability at a high thermal budget.

Low cost switching circuit for van der Pauw resistivity and Hall measurements at various temperatures

The electrical characterization of materials, particularly superconductors, semiconductors, and those undergoing metal-insulator transitions (MITs), relies significantly on resistivity and Hall measurements as a function of temperature. The van der Pauw four-point probe method is commonly used for such measurements, which involves resistance measurements for different circuit configurations connected to sample contacts. However, repeating these measurements at different temperatures is challenging and time consuming. This study introduces a novel approach utilizing a switching circuit controlled by an Arduino device and a LabVIEW program to automate resistance measurements for different electrical configurations. The effectiveness of this setup was demonstrated by testing V2O3 thin film samples deposited on Al2O3 (001) substrates using DC magnetron sputtering. The MIT temperature of the sample was 115 K during heating and 100 K during cooling. The sample exhibited p-type charge carriers with a Hall coefficient of 1.3 ± 0.1 x 10−4 cm3/C and Hall mobility of 1.7 x 10−1 cm2/V∙s, which is consistent with findings from other studies employing commercial equipment.

Analyzing Carrier Density and Hall Mobility in Impurity‐Free Silicon Virtually Doped by External Defect Placement

AbstractImpurity doping at the nanoscale for silicon is becoming less efficient with conventional techniques. Here, an alternative virtual doping method is presented for silicon that can achieve an equivalent carrier density while addressing the primary limitations of traditional doping methods. The doping for silicon is carried out by placing aluminum‐induced acceptor states externally in a silicon dioxide dielectric shell. This technique can be referred to as direct modulation doping. The resistivity, carrier density, and mobility are investigated by Hall effect measurements to characterize the carrier transport using the new doping method. The results thereof are compared with carrier transport analysis of conventionally doped silicon at room‐temperature, demonstrating a 100% increase in carrier mobility at equal carrier density. The sheet density of hole carriers in silicon due to modulation doping remains nearly constant, ≈4.7 × 1012 cm−2 over a wide temperature range from 300 down to 2 K, proving that modulation‐doped devices do not undergo carrier freeze‐out at cryogenic temperatures. In addition, a mobility enhancement is demonstrated with an increase from 89 cm2 Vs−1 at 300 K to 227 cm2 Vs−1 at 10 K, highlighting the benefits of the new method for creating emerging nanoscale electronic devices or peripheral cryo‐electronics to quantum computing.

Impact of Coulomb scattering due to trapped electrons on Hall mobilities in 4H-SiC(11 2 ¯ 0) and (1 1 ¯ 00) MOSFETs annealed in NO

Abstract The temperature dependence of Hall mobility (μ Hall) of 4H-SiC(11 2 ¯ 0) and (1 1 ¯ 00) metal-oxide-semiconductor field-effect transistors (MOSFETs) with the gate oxides annealed in NO is compared with that of MOSFETs on (0001) annealed in NO or POCl3. Coulomb scattering due to trapped electrons, which is reported to be significant in MOSFETs on (0001) annealed in NO, may be the primary limiting factor of μ Hall for MOSFETs on (11 2 ¯ 0) and (1 1 ¯ 00) annealed in NO. Furthermore, the difference in μ Hall among the MOSFETs is highlighted at 77 K, which may be attributed to the suppression of phonon scattering and the presence of strong Coulomb scattering.

Enhanced Photovoltaic Efficiency through 3D-Printed COC/Al₂O₃ Anti-Reflective Coversheets

In the past few years, there has been a considerable growth in the utilization of solar cells to produce electrical power to fulfil the growing worldwide energy demands. An optical loss is a crucial factor that impacts the performance of the photovoltaic conversion process. This loss occurs when incoming sunlight is reflected back on the outer layer of the photovoltaic cells. The application of antireflective materials on the photovoltaic substrates can enhance the absorption of sunlight and minimize the reflection. Currently, there is no ideal anti-reflective coating for solar cells that can allow the transmission of sunlight without any reflection. In this research, a transparent cyclic-olefin-copolymer (COC) was used to fabricate anti-reflection (AR) coversheet by fused deposition modelling process (3D printing). Further, the aluminium oxide Al2O3 powder was added at the proportions of 1wt%, 2wt%, 3wt%, and 4wt% to the COC polymer to increase the anti-reflection characteristics. The structural, morphological, mechanical (tear strength), electrical and temperature characteristics were studied. The performance of COC with aluminium oxide (COCA) coversheets was evaluated, and the findings revealed a considerable increment in power conversion efficiency (PCE) of 17.21% (sunlight exposure) and 18.34% (neodymium light) for COCA3 coversheets. As seen, the COCA3 sample exhibit lower electrical resistance of 3.88 ×10-3 Ω cm, carrier concentration (36.91×1020 cm-3) and higher hall mobility (13.67 cm2/Vs). The findings from the investigations demonstrated that the utilization of COC with Al2O3 powder (COCA) can be a suitable antireflective coversheet material for boosting the performance of polycrystalline silicon photovoltaic cells.

200 cm2/Vs electron mobility and controlled low 1015 cm−3 Si doping in (010) β -Ga2O3 epitaxial drift layers

We report on metalorganic chemical vapor deposition (MOCVD) growth of controllably Si-doped 4.5 μm thick β-Ga2O3 films with electron concentrations in the 1015 cm−3 range and record-high room temperature Hall electron mobilities of up to 200 cm2/Vs, reaching the predicted theoretical maximum room temperature phonon scattering-limited mobility value for β-Ga2O3. Growth of the homoepitaxial films was performed on Fe-doped (010) β-Ga2O3 substrates at a growth rate of 1.9 μm/h using TEGa as the Gallium precursor. To probe the background electron concentration, an unintentionally doped film was grown with a Hall concentration of 3.43 × 1015 cm−3 and Hall mobility of 196 cm2/Vs. Growth of intentionally Si-doped films was accomplished by fixing all growth conditions and varying only the silane flow, with controllable Hall electron concentrations ranging from 4.38 × 1015 to 8.30 × 1015 cm−3 and exceptional Hall mobilities ranging from 194 to 200 cm2/Vs demonstrated. C-V measurements showed a flat charge profile with the ND+–NA− values correlating well with the Hall-measured electron concentration in the films. SIMS measurements showed the silicon atomic concentration matched the Hall electron concentration with carbon and hydrogen below detection limit in the films. The Hall, C-V, and SIMS data indicate the growth of high-quality 4.5 μm thick β-Ga2O3 films and controllable doping into the mid 1015 cm−3 range. These results demonstrate MOCVD growth of electronics grade record-high mobility, low carrier density, and thick β-Ga2O3 drift layers for next-generation vertical β-Ga2O3 power devices.

Effect of Deposition Temperature on Zn Interstitials and Oxygen Vacancies in RF-Sputtered ZnO Thin Films and Thin Film-Transistors.

ZnO thin films were deposited using RF sputtering by varying the argon:oxygen gas flow rates and substrate temperatures. Structural, optical and electrical characterization of ZnO thin films were systematically carried out using X-Ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible spectroscopy, X-Ray photoelectron spectroscopy (XPS) and Hall measurements. Film deposited at room temperature and annealed at 300 °C exhibited low O2 incorporation with localized defects and a high percentage of Zn interstitials. A large crystalline size and fewer grain boundaries resulted in a high Hall mobility of 46.09 cm2/V-s Deposition at higher substrate temperatures resulted in improvement in O2 incorporation through the annihilation of localized defects and decrease in oxygen vacancies and Zn interstitials. Urbach tails within the bandgap were identified using the absorption spectrum and compared with the % defects from XPS. Bottom-gate thin-film transistors were subsequently fabricated on a SiO2/p-Si substrate using the combination of RF sputtering, wet etching and photolithography. Variation in the substrate temperature showed performance enhancement in terms of the leakage current, threshold voltage, sub-threshold swing and ION/IOFF ratio. Thin-film transistor (TFT) devices deposited at 300 °C resulted in an O2-rich surface through chemisorption, which led to a reduction in the leakage current of up to 10-12 A and a 10-fold reduction in the sub-threshold swing (SS) from 30 V to 2.8 V. Further TFT optimization was carried out by reducing the ZnO thickness to 50 nm, which resulted in a field-effect mobility of 1.1 cm2/V-s and ION/IOFF ratio of 105.

Fast Synthesis of Olefin-Linked Covalent Organic Frameworks via Supercritically Solvothermal Polymerization.

Covalent organic frameworks (COFs) are newly emerging yet rapidly developed porous crystalline polymeric materials, which feature topological designability, structural diversity, and porosity tunability. However, most of the reported COFs hitherto are prepared by a solvothermal method, which needs a long reaction time, especially for the olefin-linked COFs, which hinders their practical applications. Herein, we report the fast growth of olefin-linked COFs synthesized by the supercritical solvothermal method under supercritical carbon dioxide conditions. Via optimization of the reaction conditions, olefin-linked COFs are prepared within 6 h, which is period much shorter than that of the traditional solvothermal method. The as-obtained COFs feature two distinct morphologies, namely, spherical and rod-like. Interestingly, the rod-like crystal shows polarized light extinction and rebrightening phenomena, indicating the high crystallinity. After being doped with I2, the obtained I2@COFTMT-PA shows a Hall mobility of 1.94 cm2 V-1 S-1, indicating its potential applications in optoelectronics. This work expands the application of the supercritically solvothermal method to the fast growth of olefin-linked COFs and solves a long-standing challenge in chemical science, which opens up opportunities for basic research as well as practical applications of olefin-linked COFs and other polymeric materials.

Enhanced Thermoelectric Performance of Bi0.5Sb1.5Te3 through Precise Pb Doping: Analysis Using the Single Parabolic Band Model

This study investigates the thermoelectric properties of Pb-doped p-type Bi0.5Sb1.5Te3 alloys using the Single Parabolic Band (SPB) model, focusing on optimizing room-temperature performance. We systematically analyze the effects of Pb doping (0, 0.49, 0.65, 0.81, 0.97, and 1.3 at%) on key parameters including density-of-states effective mass (md *), non-degenerate mobility (μ0), weighted mobility (μw), and the thermoelectric quality factor (B-factor) at 323 K. The results reveal that md * reaches a maximum of 1.37 me at 0.97 at% Pb doping, representing a 22.25 % increase over the pristine sample. The highest μ0 of 234.5 cm2 V-1 s-1 is achieved at 0.65 at% Pb, highlighting the complex relationship between doping and carrier mobility. Notably, 0.97 at% Pb doping optimizes thermoelectric performance, yielding the highest μw, power factor, and B-factor. This composition also minimizes lattice thermal conductivity (k1) by 44.93 % compared to the undoped sample, significantly reducing phonon heat conduction. The Callaway-von Baeyer model corroborates these findings, indicating maximized point defect scattering at 0.97 at% Pb. A theoretical peak figure-of-merit (zT) of 1.74 is thus predicted at this doping level, demonstrating a possible substantial enhancement in thermoelectric efficiency upon appropriate carrier concentration tuning. The observed trends in Seebeck coefficient, Hall carrier concentration, and Hall mobility with increasing Pb content provide insights into the underlying mechanisms of performance enhancement. This comprehensive study highlights the critical role of precise Pb doping in optimizing the thermoelectric properties of Bi0.5Sb1.5Te3 alloys for room-temperature applications and establishes a framework for future investigations into similar material systems.

Effects of off-axis angles of 4H-SiC substrates on properties of β-Ga2O3 films grown by low-pressure chemical vapor deposition

In this work, β-Ga2O3 films with (−201) preferred orientation were heteroepitaxially grown on SiC substrates with off-axis angles of 0°, 4° and 8° by low-pressure chemical vapor deposition (LPCVD). It is found that the crystal quality, surface morphology, electrical properties of the β-Ga2O3 films of the film are significantly sensitive to the off-axis angle of SiC substrates. The crystal quality and surface morphology of the film were significantly improved when the 4° off-axis substrate was used, of which the FWHM (Full width at half maximum) was as low as 0.169° and the Ra (Roughness Average) of the smooth surface was 1.98 nm. Due to the improvement of crystal quality, the Hall mobility of the films deposited on 4° off-axis substrates was increased to 50.88 cm2/V·s. The photoluminescence peak intensity of the film increases first and then decreases with the increase of the off-axis angle of the substrate. However, the use of the off-axis substrate has no obvious effect on the oxygen vacancy ratio of the films. The results of this study demonstrate the significance for the preparation of high quality heteroepitaxial β-Ga2O3 films on SiC substrate for the promising applications in power electronic and optoelectronic devices.

Single Crystalline GeSe Van Der Waals Ribbons With Uniform Layer Stacking, High Carrier Mobility, and Adjustable Edge Morphology.

Performance of the group IV monochalcogenide GeSe in solar cells, electronic, and optoelectronic devices is expected to improve when high-quality single crystalline material is used rather than polycrystalline films. Crystalline flakes represent an attractive alternative to bulk single crystals as their synthesis may be developed to be scalable, faster, and with higher overall yield. However, large - and especially large and thin - single crystal flakes are notoriously hard to synthesize. Here it is demonstrated that vapor-liquid-solid growth combined with direct lateral vapor-solid incorporation produces high-quality single crystalline GeSe ribbons with tens of micrometers size and controllable thickness. Electron microscopy shows that the ribbons exhibit perfect equilibrium (AB) van der Waals stacking order without extended defects across the entire thickness, in contrast to the conventional case of substrate-supported flakes where material is added via layer-by-layer nucleation and growth on the basal plane. Electrical measurements show anisotropic transport and a high Hall mobility of 85 cm2V-1s-1, on par with the best single crystals to date. Growth from mixed GeSe and SnSe vapors, finally, yields ribbons with unchanged structure and composition but with jagged edges, promising for applications that rely on ample chemically active edge sites, such as catalysis or photocatalysis.

ScAlInN/GaN heterostructures grown by molecular beam epitaxy

Rare-earth (RE) elements doped III-nitride semiconductors have garnered attention for their potential in advanced high-frequency and high-power electronic applications. We report on the molecular beam epitaxy of quaternary alloy ScAlInN, which is an encouraging strategy to improve the heterointerface quality when grown at relatively low temperatures. Monocrystalline wurtzite phase and uniform domain structures are achieved in ScAlInN/GaN heterostructures, featuring atomically sharp interface. ScAlInN (the Sc content in the ScAlN fraction is 14%) films with lower In contents (less than 6%) are nearly lattice matched to GaN, exhibiting negligible in-plane strain, which are excellent barrier layer candidates for GaN high electron mobility transistors (HEMTs). Using a 15-nm-thick Sc0.13Al0.83In0.04N as a barrier layer in GaN HEMT, a two-dimensional electron gas density of 4.00 × 1013 cm−2 and a Hall mobility of 928 cm2/V s, with a corresponding sheet resistance of 169 Ω/□, have been achieved. This work underscores the potential of alloy engineering to adjust lattice parameters, bandgap, polarization, interfaces, and strain in emerging RE-III-nitrides, paving the way for their use in next-generation optoelectronic, electronic, acoustic, and ferroelectric applications.

Enhancing solar cell productivity with MgAl2O4–ZnAl2O4 blended anti-reflection coatings

The enhancement of productivity in solar cells primarily relies on the application of anti-reflection coatings. The current research employs coating materials such as MgAl2O4, ZnAl2O4 and blended MgAl2O4–ZnAl2O4 as an anti-reflective layer on the monocrystalline Si solar cells by employing RF sputter coating method. Magnesium nitrate hexahydrate and aluminium nitrate nonahydrate were utilized for the synthesis of MgAl2O4 by the sol-gel technique. ZnAl2O4 was synthesized using zinc nitrate hexahydrate and aluminum nitrate nonahydrate by sol–gel procedure. The performance of coated photovoltaic cells was evaluated through different characterization techniques. From the optical study, the blended MgAl2O4-ZnAl2O4 coating shows the maximum absorbance of around 93 % and lowest reflectance of 9 %. The MgAl2O4–ZnAl2O4 blend achieves a maximum power conversion efficiency (PCE) of 22.12 % in a controlled light source and 19.21 % in direct sunlight. Compared to other solar cells, blended MgAl2O4–ZnAl2O4 demonstrates low resistivity (4.23 × 10−3 Ω-cm), high carrier concentration (35.81 × 1020 cm−3) and maximum hall mobility (12.96 cm2/Vs). From the surface temperature measurement, it is evident that the MgAl2O4–ZnAl2O4 blend coated solar cell exhibits lowest temperature of 38.2 °C under simulated light. The experimental results indicate that the blended MgAl2O4–ZnAl2O4 coated photovoltaic cells exhibits superior productivity than the various coated and uncoated solar cells. Therefore, it can be stated that MgAl2O4–ZnAl2O4 blends are the excellent antireflective materials for achieving desired PCE in solar photovoltaic cells.

The Effect of Concentration of Aluminum on Structural, Optical, and Electrical Properties of Aluminum‐doped ZnO Nanostructures Electrochemically Deposited on Polyimide

AbstractAluminum‐doped ZnO (AZO) were successfully prepared on polyimide (PI) film using electrochemical deposition. Field emission scanning electron microscopy (FESEM) analysis revealed that as the aluminum concentration increased, the morphology of AZO nanostructures changed from pellets to nanorods. X‐ray photoelectron spectrometry (XPS) was employed to study the chemical states of undoped and Al‐doped ZnO on a polyimide substrate. The X‐ray diffraction (XRD) patterns of the PI/AZO nanostructures showed a polycrystalline wurtzite structure with a crystallographic orientation along the (002) plane. The XRD analysis also indicated that the average crystallite size decreased from 50.5 nm to 31.0 nm with increasing aluminum concentration (from 0.05 mM to 10 mM). Transmittance analysis revealed that with increasing aluminum concentration, the average optical transmittance in the visible region decreased from 90 % to 75 %. The aluminum concentration has a significant effect on the electrical properties of the samples, as shown by current‐voltage (I–V) and Hall measurements. Among the samples, the AZO/PI film prepared with 5 mM aluminum concentration exhibited the minimum electrical resistivity (4.14×10−2 Ω.cm), the highest carrier density (1.10×1021 cm−3) and the Hall mobility (5.40 cm2 V−1 s−1). We also discuss the possible mechanisms underlying these results compared to undoped ZnO films. This study contributes to the potential applications in flexible electronics and optoelectronics by demonstrating the tunability of AZO nanostructures on a flexible polyimide substrate through controlled aluminum doping.

Effects of opto-electronics properties of CeMnO2 nanoparticles improve the efficiency of CeMnO2/MAFASnBrI3/BaSi2 photovoltaic cells

In this paper, we synthesized manganese-substituted cerium oxide (CeMnO2) electron transport layer (ETL) nanomaterial via the co-precipitation method using various Mn compositions. These variations resulted in significant changes in the physical, optical, electronic, and dielectric properties of the CeMnO2 nanoparticles. The hexagonal structure of the CeMnO2 nanoparticles was validated using X-ray diffraction (XRD). Their morphology and surface characteristics were analyzed through scanning electron microscopy (SEM). Ultraviolet–visible (UV–Vis) spectrophotometry was utilized to explore their optoelectronic properties, revealing an increase in transmittance from 75 % to 90 %, along with corresponding decreases in reflectance and absorbance. Moreover, the energy bandgap (Eg) increased from 3.68 to 3.86 eV, while the Urbach energy (EU) rose from 0.18 to 0.6 eV with varying Mn compositions. The increase in defect quantity is associated with the reduction in both DC and AC conductivity observed with higher Mn compositions. Using a Hall effect instrument, we measured the sheet resistance, Hall mobility (ranging from 35.20 to 62.32 cm2 V−1 s−1), and carrier concentration (from 8.71 × 1018 to 1.22 × 1020 cm−3) of the CeMnO2 nanomaterials. The second stage focused on developing a high-efficiency (CeMnO2/MAFASnBrI3/BaSi2) solar cell based on experimental data from the CeMnO2 ETL and BaSi2 HTL materials. After multiple optimizations of the proposed solar cells, we achieved a 27.73 % efficiency.

Influence of fixed charges and trapped electrons on free electron mobility at 4H-SiC(0001)/SiO2 interfaces with gate oxides annealed in NO or POCl3

Free electron mobility (μ free) in 4H-SiC(0001) MOSFETs with gate oxides annealed in NO or POCl3 was calculated in a wide range of effective normal field (E eff) from 0.02 to 2 MV cm−1, taking account of scattering by fixed charges and trapped electrons. The present calculation indicates that the Hall mobility in the high-E eff region experimentally obtained for NO-annealed MOSFETs (14 cm2 V−1 s−1 at 1.1 MV cm−1) is much lower than that for POCl3-annealed MOSFETs (41 cm2 V−1 s−1) due to severe Coulomb scattering by electrons trapped at a very high density of interface states.

Analysis of Local Properties and Performance of Bilayer Epitaxial Graphene Field Effect Transistors on SiC.

Epitaxial bilayer graphene, grown by chemical vapor deposition on SiC substrates without silicon sublimation, is crucial material for graphene field effect transistors (GFETs). Rigorous characterization methods, such as atomic force microscopy and Raman spectroscopy, confirm the exceptional quality of this graphene. Post-nanofabrication, extensive evaluation of DC and high-frequency properties enable the extraction of critical parameters such as the current gain (fmax) and cut-off frequency (ft) of hundred transistors. The Raman spectra analysis provides insights into material property, which correlate with Hall mobilities, carrier densities, contact resistance and sheet resistance and highlights graphene's intrinsic properties. The GFETs' performance displays dispersion, as confirmed through the characterization of multiple transistors. Since the Raman analysis shows relatively homogeneous surface, the variation in Hall mobility, carrier densities and contact resistance cross the wafer suggest that the dispersion of GFET transistor's performance could be related to the process of fabrication. Such insights are especially critical in integrated circuits, where consistent transistor performance is vital due to the presence of circuit elements like inductance, capacitance and coplanar waveguides often distributed across the same wafer.

Tuning the Topo-Morphological properties of ITO Films using Al-Ag interlayer for Low-Resistance Optoelectronics Devices

Indium tin oxide (ITO) is recently attracting intense attention for application as transparent conducting electrode in different optoelectronic devices including solar cells, liquid crystal displays and organic light emitting diodes. This is attributed to their high optical transmittance in the visible region and good electrical conductivity. In this work, surface topological-morphological (topo-morphological) and electrical properties of ITO based multilayer films with aluminum-silver (Al-Ag) metal interlayer (ITO/Al-Ag/ITO) are investigated after post annealing treatment at 300-500oC by atomic force microscopic (AFM), field emission scanning electron microscopy (FESEM), four-point probe and hall-effect techniques respectively. The ITO/Al-Ag/ITO films are deposited by direct current and radio frequency magnetron sputtering techniques on p-type Si at room temperature. The results showed a smooth surface topology by as-deposited film with films smoothness improving after post annealing treatment as analyzed by AFM method. Sharp crystallites peaks were obtained by all the films with smaller peaks diffusing and recombining to form larger films with increasing post-annealing temperature. The films root means square roughness increased as the temperature increases with film annealed at 500oC showing a superior and enhanced microstructure. Compared to as-deposited film, careful observation shows that surface morphology smoothness increased with increase in temperature with films annealed at 400oC and 500oC showing highest increasing surface smoothness pattern as determined by FESEM technique. Similarly, higher grain sizes are observed especially by films annealed at 400oC and 500oC due to the heat absorption which causes the particles to expand thereby narrowing the grain boundaries and subsequently improve the surface smoothness. These FESEM findings are consistent with AFM measurements confirming the high surface property and enhanced grain size with increasing post annealing temperature. The films exhibit decreased electrical resistivity and sheet resistance while carrier concentration and Hall mobility increased with increasing post annealing treatment indicating highest corresponding values of...

Characterization of induced quasi-two-dimensional transport in n-type InxGa1−xAs1 − yBiy bulk layer

The temperature-dependent transport properties of n-type InGaAsBi epitaxial alloys with various doping densities are investigated by conducting magnetoresistance (MR) and Hall Effect (HE) measurements. The electronic band structure of the alloys and free electron distribution were calculated using Finite Element Method (FEM). Analysis of the oscillations in the transverse (Hall) resistivity shows that quasi-two-dimensional electron gas (Q-2D) in the bulk InGaAsBi epitaxial layer (three-dimensional, 3D) forms at the sample surface under magnetic field even though there is no formation of the spacial two-dimensional electron gas (2DEG) at the interface between InGaAs and InP:Fe interlayer. The formation of Q-2D in the 3D epitaxial layer was verified by temperature and magnetic field dependence of the resistivity and carrier concentration. Analysis of Shubnikov-de Haas (SdH) oscillations in longitudinal (sample) resistivity reveals that the electron effective mass in InGaAsBi alloys are not affect by Bi incorporation into host InGaAs alloys, which verifies the validity of the Valence Band Anti-Crossing (VBAC) model. The Hall mobility of the nondegenerate samples shows the conventional 3D characteristics while that of the samples is independence of temperature for degenerated samples. The scattering mechanism of the electrons at low temperature is in long-range interaction regime. In addition, the effects of electron density on the transport parameters such as the effective mass, and Fermi level are elucidated considering bandgap nonparabolicity and VBAC interaction in InGaAsBi alloys.

Substrate-dependent carrier mobility in polycrystalline Ge thin films

We present the effect of substrate choice on the carrier mobility of polycrystalline Ge thin films on SiO2/Si, C-cut sapphire, and R-cut sapphire substrates. The Hall mobility of the polycrystalline Ge thin films exhibited a strong correlation with the substrates, with mobility increasing sequentially for Ge thin films on SiO2/Si, C-cut sapphire, and R-cut sapphire substrates. Hall Effect measurements further suggested minimal influence of grain boundary scattering. Electron backscatter diffraction analysis revealed similar grain sizes of ∼200 nm across different substrates, but distinct grain orientation distributions, particularly with pronounced (110) grains on R-cut sapphire substrates. This work sheds light on the importance of substrate selection in optimizing the electrical performance of polycrystalline Ge thin films and highlights avenues for further investigation in understanding the underlying mechanisms governing substrate-dependent carrier mobility.