Increase In Carrier Concentration Research Articles

Divacancy and resonance level enables high thermoelectric performance in n-type SnSe polycrystals.

N-type polycrystalline SnSe is considered as a highly promising candidates for thermoelectric applications due to facile processing, machinability, and scalability. However, existing efforts do not enable a peak ZT value exceeding 2.0 in n-type polycrystalline SnSe. Here, we realized a significant ZT enhancement by leveraging the synergistic effects of divacancy defect and introducing resonance level into the conduction band. The resonance level and increased density of states resulting from tungsten boost the Seebeck coefficient. The combination of the enhanced electrical conductivity (achieved by increasing carrier concentration through WCl6 doping and Se vacancies) and large Seebeck coefficient lead to a high power factor. Microstructural analyses reveal that the co-existence of divacancy defects (Se vacancies and Sn vacancies) and endotaxial W- and Cl-rich nanoprecipitates scatter phonons effectively, resulting in ultralow lattice conductivity. Ultimately, a record-high peak ZT of 2.2 at 773 K is achieved in n-type SnSe0.92 + 0.03WCl6.

Uniformity of Thermoelectric Properties of N-type Bi<sub>2</sub>Te<sub>3-y</sub>Se<sub>y</sub> Bulky Compacts

Because n-type Bi<sub>2</sub>Te<sub>3</sub>-based materials exhibit lower thermoelectric performance than p-type materials and because their thermoelectric properties are sensitively changed by the composition and carrier concentration, optimizing these aspects in n-type materials is necessary to improve the thermoelectric figure of merit (ZT). In this study, the thermoelectric performance of n-type Bi<sub>2</sub>Te<sub>3</sub>-based materials was improved by reducing thermal conductivity through the formation of a Bi<sub>2</sub>Te<sub>3</sub>-Bi<sub>2</sub>Se<sub>3</sub> solid solution, Bi<sub>2</sub>Te<sub>3-y</sub>Se<sub>y</sub> and optimizing the carrier concentration through doping. As the amount of Se increased in Bi<sub>2</sub>Te<sub>3-y</sub>Se<sub>y</sub>, the carrier concentration decreased, resulting in decreased electrical and thermal conductivities and increased Seebeck coefficients. As a result, Bi<sub>2</sub>Te<sub>2.85</sub>Se<sub>0.15</sub> exhibited ZT = 0.56 at 323 K, and Bi<sub>2</sub>Te<sub>2.4</sub>Se<sub>0.6</sub> exhibited ZT = 0.60 at 423 K. Among the Bi<sub>2</sub>Te<sub>3-y</sub>Se<sub>y</sub> solid solutions, the doping effect was investigated for Bi<sub>2</sub>Te<sub>2.85</sub>Se<sub>0.15</sub> and Bi<sub>2</sub>Te<sub>2.7</sub>Se<sub>0.3</sub>, which recorded excellent thermoelectric performance at low temperatures. When halogen element (I) was doped, the power factor improved owing to the increase in carrier concentration, and the thermal conductivity decreased. As a result, the ZT values were greatly enhanced to ZT = 0.90 at 423 K for Bi<sub>2</sub>Te<sub>2.85</sub>Se<sub>0.15</sub>:I<sub>0.005</sub> and ZT = 1.13 at 423 K for Bi<sub>2</sub>Te<sub>2.7</sub>Se<sub>0.3</sub>:I<sub>0.0075</sub>. When the transition elements (Cu and Ag) were doped, the power factor was improved by the increase in Seebeck coefficient, and thereby Bi<sub>2</sub>Te<sub>2.85</sub>Se<sub>0.15</sub>:Ag<sub>0.01</sub> and Bi<sub>2</sub>Te<sub>2.85</sub>Se<sub>0.15</sub>:Ag<sub>0.01</sub> exhibited ZT = 0.76 and ZT = 0.75 at 323 K, respectively, and Bi<sub>2</sub>Te<sub>2.7</sub>Se<sub>0.3</sub>:Cu<sub>0.01</sub> exhibited ZT = 0.73 at 423 K. Conversely, doping with other transition elements (Ni and Zn), as well as group-III (Al and In) and group-IV (Ge and Sn) elements, resulted in power factors and thermal conductivities that were similar to or slightly less than those of undoped Bi<sub>2</sub>Te<sub>2.85</sub>Se<sub>0.15</sub>, leading to minimal or no improvement in ZT. Next, n-type Bi<sub>2</sub>Te<sub>2.85</sub>Se<sub>0.15</sub>:I<sub>0.005</sub> and Bi<sub>2</sub>Te<sub>2.7</sub>Se<sub>0.3</sub>:I<sub>0.0075</sub>, which exhibited the best thermoelectric performances, were fabricated as bulky compacts, and the uniformity of their thermoelectric properties were evaluated.

Heat-Annealed Zinc Oxide on Flexible Carbon Nanotube Paper and Exposed to Gradient Light to Enhance Its Photoelectric Response.

Buckypaper (BP), a flexible and porous material, exhibits photovoltaic properties when exposed to light. In this study, we employed radio frequency (RF) sputtering of zinc oxide (ZnO) followed by rapid thermal annealing to enhance the photovoltaic response of BP. We investigated the impact of various sputtering parameters, such as the gas flow ratio of argon to oxygen and deposition time, on the morphology, composition, resistivity, and photovoltaic characteristics of ZnO-modified BP. Additionally, the photovoltaic performance of the samples under different illumination modes and wavelengths was compared. It was found that optimal sputtering conditions-argon to oxygen flow ratio of 1:2, deposition time of 20 min, and power of 100 watts-resulted in a ZnO film thickness of approximately 45 nanometers. After annealing at 400 °C for 10 min, the ZnO-modified BP demonstrated a significant increase in photocurrent and photovoltage, along with a reduction in resistivity, compared to unmodified BP. Moreover, under gradient illumination, the ZnO-modified BP exhibited a photovoltage enhancement of 14.70-fold and a photocurrent increase of 13.86-fold, compared to uniform illumination. Under blue light, it showed a higher photovoltaic response than under other colors. The enhancement in photovoltaic response is attributed to the formation of a Schottky junction between ZnO and BP, an increased carrier concentration gradient, and an expanded light absorption spectrum. Our results validate that ZnO sputtering followed by annealing is an effective method for modifying BP for photovoltaic applications such as solar cells and photodetectors.

Correlation between structural, morphological, and electrical transport properties of nano-dimensional Tellurium thin film by low energy ion beam irradiation

Tellurium (Te), an emerging semiconductor material, exhibits intriguing physical properties in low-dimensional forms. This study investigates the structural, morphological, and transport properties of low-dimensional Te thin film deposited by physical vapor deposition after 400 keV Kr2+ ion irradiation with varying fluences of 1 × 1013, 5 × 1013, and1 × 1014 ions-cm−2. The X-ray diffraction (XRD) pattern reveals the hexagonal phase of pristine Te. As ion fluence increases, intensity of the XRD peaks decreases and the full-width half maxima (FWHM) increases, indicating a reduction in crystallinity. The intensity of the Raman peak decreases upon irradiation, resulting in a red shift in the spectra of the irradiated sample. The evolution of morphology at different fluences has been examined with atomic force microscopy (AFM) measurements. The results indicate the segregation of grains and an increase in root mean square (RMS) roughness from 2.59 pm to 5.11 pm with ion fluence up to 5 × 1013 ions-cm−2. At the highest fluence, i.e., 1 × 1014 ions-cm−2, there is an agglomeration of grains, and hence a decrease in RMS roughness to 3.92 pm is observed. The DC resistivity measurement indicates the semiconducting nature of all films. Additionally, this measurement signifies the rapid decrease in activation energy at both band-to-band conduction and nearest neighbour hopping (NNH) conduction. Following irradiation, Hall measurement demonstrates a decrease in the concentration of charge carriers and an increase in resistivity due to scattering originating from grain boundaries. However, when the fluence is increased to 1 × 1014 ions-cm−2, there is a reduction in resistivity and an increase in carrier concentration with enhanced Hall mobility in comparison to pristine Te. Therefore, this study showcases that low-energy ion irradiation has a significant impact on the modification of the structure, morphology, and electrical transport properties of semiconducting Te thin film.

Re-optimising the thermoelectric properties of BiTeSe by CuO doping: From zone-melting ingots to powder metallurgy bulks with a large size

The Bi2Te3-based thermoelectric crystal ingots produced by the zone-melting (ZM) are the most widely used commercially at present. However, the poor mechanical properties caused by the ZM are unfavorable to the production of miniature devices. The mechanical properties can be improved by the powder metallurgy (PM), but the PM results in performance degradation of n-type Bi2Te3-based alloys, which could be attributed to the disappearance of intrinsic anisotropy and the increased carrier concentration originated from the “donor-like” effect of grain boundary. In this paper, the Bi2Te2.7Se0.3 + 4 wt% Te (BTST) powder was from the ground ZM ingots, and the influence of CuO doping on the thermoelectric properties of hot-pressed BTST polycrystalline bulks with a large size was investigated. It can be found that the thermoelectric properties of BTST are improved remarkably by CuO doping due to the increased Seebeck coefficient and suppressed thermal conductivity, which is caused by the synthetic effects of optimised carrier concentration, increased effective mass, and enhanced phonon scattering by the Cu2Te/Bi2Te2.7Se0.3 hetero-interfaces. Finally, the dimensionless thermoelectric figure of merit (ZT) of the sample (CuO)0.1(Bi2Te2.7Se0.3 + 4 wt% Te) reaches 1.32 at 408 K, which is about 65 % higher than that of the pristine BTST, and its average ZTave value reaches 1.27 in the temperature range of 300–473 K. The large size bulks produced by this method are not only commercialized directly, but also avoid the problem of poor mechanical properties.

Tuning Spin-Polarized Lifetime at High Carrier Density through Deformation Potential in Dion-Jacobson-Phase Perovskites.

The control of spin relaxation mechanisms is of great importance for spintronics applications as well as for fundamental studies. Layered metal-halide perovskites represent an emerging class of semiconductors with rich optical spin physics, showing potential for spintronic applications. However, a major hurdle arises in layered metal-halide perovskites with strong spin-orbit coupling, where the spin lifetime becomes extremely short due to D'yakonov-Perel' scattering and Bir-Aronov-Pikus at high carrier density. Using the circularly polarized pump-probe transient reflection technique, we experimentally reveal the important scattering for spin relaxation beyond the electron-hole exchange strength in the Dion-Jacobson (DJ)-type 2D perovskites (3AMP)(MA)n-1PbnI3n+1 [3AMP = 3-(aminomethyl)piperidinium, n = 1-4]. Despite a more than 10-fold increase in carrier concentration, the spin lifetimes for n = 3 and 4 are effectively maintained. We reveal neutral impurity and polar optical phonon scatterings as significant contributors to the momentum relaxation rate. Furthermore, we show that more octahedral distortions induce a larger deformation potential which is reflected on the acoustic phonon properties. Coherent acoustic phonon analysis indicates that the polaronic effect is crucial in achieving control over the scattering mechanism and ensuring spin lifetime protection, highlighting the potential of DJ-phase perovskites for spintronic applications.

High performance dual-mode module for power generation and cooling based on optimized BiSbTe

Bismuth telluride is currently the most outstanding thermoelectric (TE) material near room temperature, and the high demand for solid-state refrigeration and low-grade waste heat recovery means there is an urgent need to improve its TE performance. This study investigates the enhanced TE performance of Bi0.4Sb1.6Te3 through the addition of Ag2Se. The introduction of Ag promotes an acceptor doping effect, leading to increased carrier concentration, while inhibiting lattice thermal conductivity together with Se doping. As a result, a notable enhancement in the figure of merit (ZT) to 1.35 at 373 K is achieved, with an average ZT of 1.17 spanning temperatures from 300 K to 523 K. More significantly, a 7-pair TE module was integrated using p-type Bi0.4Sb1.6Te3-0.00125Ag2Se and n-type extruded BiTeSe for cooling and power generation. A competitive conversion efficiency of 5.54 % at a temperature difference of 230 K and a maximum cooling temperature difference of 63.1 K at Th = 300 K are achieved, demonstrating the enormous practical application potential of this dual-mode module.

Low temperature one-step synthesis of Ag nanoparticles on BaTiO3 for synergistic piezo-photocatalytic properties

It is a major constraint that complex synthesis methods limit the application of catalysts. Herein, Ag/BaTiO3 catalyst is synthesized via a facile method, which demonstrates the outstanding catalytic properties. Investigations reveal that Ag-loading BaTiO3 could increase carrier concentration, reduce the electronic impedance and enhance carrier’s separation efficiency under ultrasonic vibration, leading to superior piezocatalytic performance. Therefore, Ag/BaTiO3 catalyst presents the high degradation efficiency of 95.4 % in 50 min for RhB dye solution at light illumination and ultrasonic vibration. Moreover, when Ag content is 0.33 %, the degradation ratio of the sample still remains 81.9 % after 5th cycles, which indicates Ag/BaTiO3 catalyst has good stability. This work provides a novel and easy implement strategy for designing high performance catalysts, and could be extended to other catalytic material.

Enhanced thermoelectric performance of Cu2SnSe3 by synergic effects via cobalt-doping

Diamond-like Cu2SnSe3 has drawn intensive attention as an excellent environmentally-friendly p-type thermoelectric material. In this study, the effects of Co-doping at Sn site on its thermoelectric properties were investigated. Results revealed an effective increase in carrier concentration and enhancement of density-of-states (DOS) effective mass m* due to the role of Co as acceptor and probably the contribution of its d states in the valence bands. Consequently, a remarkable power factor of up to 9.55 μW cm−1 K−2 has been achieved at 823 K. In addition, lattice thermal conductivity was strongly suppressed due to the intensified phonon scattering and softening of bonding as revealed by the sound velocity analysis. Ultimately, a maximal ZT of 0.97 at 823 K and an average ZT of ∼ 0.7 have been achieved in Cu2Sn0.88Co0.12Se3, almost double that of the pristine one.

Tunability of the photoelectric properties of CdSe thin films through doping with manganese toward photovoltaic applications

Tandem solar cells have been demonstrated to surpass the Shockley-Queisser limit, promising the transition to third-generation solar cell technology. Tandem solar cells comprise thin film layers of various band gap semiconductors, and CdSe is a promising candidate for the top cell. In this study, we explore the properties of thermally evaporated CdSe thin films doped with 0 to 5 wt% Mn and report a significant five-fold increase in carrier concentration. Furthermore, our optoelectrical studies indicate a band gap energy of 1.681eV, experiencing up to a 28 meV shift with 5 wt% Mn doping and identifies 1 wt% as the optimal doping concentration, offering the best electrical properties and photo-response while maintaining a stable band gap.

A significant increase in carrier concentration in TiO2 by Sm doping

Sm-doped TiO2 thin films were synthesized by pulsed laser deposition. The luminescence and donor-generation properties of thin films annealed at various temperatures were investigated. The results showed that Sm-related emissions occurred in the temperature range 500 °C–800 °C. The donor densities in this temperature range were two orders of magnitude higher than that of the undoped TiO2 thin film. The effect of annealing within the temperature window indicates a local fine structural transition of the ligands around Sm3+ ions from T d symmetry to the lower C 4v one; these ions are effective luminescence centers in TiO2:Sm thin films. This local structural distortion also increases defect generation, and this increases the donor density in the same temperature region.

Optical properties of Sn-substituted GeTe phase-change materials under high pressure

The emerging phase change materials (PCMs) have attracted much attention due to their unique properties and applications. However, the optical properties of PCM at high pressures have not been well explored. In this work, the microstructure and optical properties of GeTe and Sn-substituted GeTe at high pressures up to 30 GPa have been systematically investigated. We find that the substitution of small amounts of Sn for Ge combined with the introduction of high pressure can induce an optical contrast of 117% in crystalline GeTe, which is even higher than the highest optical contrast reported so far (90%) caused by amorphous GeTe to crystalline GeTe. The pressure-induced contrast does not originate from any phase transition as previously, but from the combined effect of Peierls distortion elimination and Ge vacancy formation, which leads to an increase in carrier concentration. The relationship between pressure/atomic composition, Peierls distortion/vacancy formation, and optical contrast can be well explained by a combination of experiments and theoretical calculations. Therefore, this study reveals the effect of high pressure on the optical properties of PCMs and provides new ideas for the design of high-optical-contrast PCMs.

Improving the quality and properties of GaInSb crystal with Al doping

GaInSb crystal is a promising substrate material that can be used to prepare various high-performance devices. Ga0.86In0.14Sb and Al-doped Ga0.86In0.14Sb (Ga0.86In0.14Sb:Al) crystals were grown with the vertical Bridgman method (VB). The doping concentration of aluminum (Al) is 0.005–0.015 molar ratio. The effect of Al doping on the structure and properties of Ga0.86In0.14Sb crystal was studied. The results indicated that Al doping significantly reduced the segregation of indium (In) component in the crystal, with the radial segregation reaching a minimum of 0.051 mol% mm−1 and the axial segregation reaching a minimum of 0.067 mol% mm−1. The doping of Al also improved the crystal quality (lattice structure integrity) of Ga0.86In0.14Sb. The passivation and compensation of Al on the intrinsic defects of Ga0.86In0.14Sb crystal significantly inhibited the generation of dislocation, of which density decreased to 2.461 × 103 cm−2. The doping of Al as the equivalent electron element of gallium (Ga) and In not only made the carrier concentration increase to 1.848 × 1018 cm−3 but also made the carrier mobility increase to 1.982 × 103 cm2/(V·s), resulting in the resistivity decreasing to 1.261 × 10−3 Ω·cm.

Ni doping induced property enhancement in laser ablated BaSnO3 films suitable for optoelectronic applications

Pulsed laser deposition is a straightforward approach for preparing films with superconducting to dielectric properties with atomic layer precision. The deep-seated mechanisms involved in the particle transport from target to substrate and subsequent film formation still need to be fully comprehended. This manuscript reports the property enhancement observed in laser ablated perovskite BaSnO3 films with Ni doping. Films' crystallinity improvement is observed, and an intensity enhancement of 1150% is observed on 3 mol% Ni-doping. The optimum Ni-doping concentration in BaSnO3 is found to be 3 mol%. Herein, Ni-doped BaSnO3 films deposited by PLD showed an unusual increase in film thickness (i.e., from 615 nm in the pure film to 1317 nm in the film with 7 mol% Ni-doping as revealed by lateral SEM analysis and spectroscopic ellipsometry). We propose an “Induced Magnetic field-assisted Particle Convergence (IMPC)” effect for this superficial growth enhancement. The film's optical properties are modified with an increased nickel doping level, and the bandgap energy shows renormalization. All the films show excellent transmittance (80–90%) in the Vis.-NIR region. Hall-effect measurement reveals the increased carrier concentration by three orders (2.98 × 1011 to 3.50 × 1014 cm−3). In addition, the enhancement in mobility from 3.13 to 20.93 cm2V−1s−1 and a decrease in electrical resistivity by six orders (i.e., from 4.05 × 109 to 1.13 × 103 Ω cm) are observed on 7 mol% Ni doping. XPS measurements reveals that the Ba, Sn and Ni ions are at 2+, 4+ and 2+ oxidation states. Using spectroscopic ellipsometric method, we estimated the optical constants of the films, the refractive index, dielectric constant, and extinction coefficient show a normal dispersion behavior. The high crystallinity, high transmittance, suitable surface topography, and improved electrical performances of the Ni-doped BaSnO3 films make them excellent candidates for optoelectronic devices and solar cells.

Enhancing charge transport and photoluminescence characteristics via transition metals doping in ITO thin films

Abstract This study presents the synthesis and characterization of pristine and transition metal (Co, Fe, and Zr)-doped indium tin oxide (ITO) thin films fabricated via RF magnetron sputtering. The effect of transition metal doping on ITO thin films properties was comprehensively examined using numerous spectroscopic and microscopic methods such as XRD, FTIR, and SEM coupled with EDX, UV–visible and PL spectroscopy, and four-probe and J–V measurements. The cubic crystal structure of the materials was confirmed through XRD spectroscopy, while FTIR results validated the existence of chemical bonds, signified by sharp peaks at 608 cm−1 and 667 cm−1 in the fingerprint region. SEM imaging revealed a granular-like agglomerated structure, with EDX confirming the elemental composition of the samples. The incorporation of Co, Fe, and Zr ions into ITO is aimed at improving photoconductivity and the optical bandgap, with the ultimate objective of enhancing performance in photovoltaic applications. Our findings showed a significant decrease in optical transmission in the visible spectrum. The bandgap also experienced a minor decrease from 3.67 eV to 3.53 eV. Analysis of the photoluminescence spectra exhibited the majority of emission peaks in the UV region, ascribed to electronic transitions occurring via band-to-band and band-to-impurity interactions within the ITO. Electrical measurements indicated lower resistance, higher current flow, and increased carrier concentration in transition metals–doped ITO compared to the undoped ITO, with Zr-doped ITO exhibiting the highest conductivity and optimal charge flow among all dopants. These promising findings in terms of optical, structural, and electrical attributes signal the potential of these materials for photovoltaic system applications.

Atomic‐resolution Interfacial Microstructure and Thermo‐electro‐magnetic Energy Conversion Performance of Gd/Bi0.5Sb1.5Te3 Composites

Thermo‐electro‐magnetic materials with simultaneously large magnetocaloric (MC) and thermoelectric (TE) effects are the core part for designing TE/MC all‐solid‐state cooling devices. Compositing MC phase with TE material is an effective approach. However, the elemental diffusion and chemical reaction occurring at the two‐phase interfaces could significantly impair the cooling performance. Herein, Gd/Bi0.5Sb1.5Te3 (Gd/BST) composites were prepared by a low‐temperature high‐pressure spark plasma sintering method with an aim to control the extent of interfacial reaction. The reaction of Gd with the diffusive Te and the formation of GdTe nanocrystals were identified at the Gd/BST interfaces by the atomic‐resolution microscope. The formed antisite defects and enhanced {000 l} preferential orientation in BST are responsible for the increased carrier concentration and mobility, which leads to optimized electrical properties. The heterogeneous interface phases, along with antisite defects, favor the phonon scattering enhancement and lattice thermal conductivity suppression. The optimized composite sintered at 693 K exhibited a maximum ZT of 1.27 at 300 K. Furthermore, the well‐controlled interfacial reaction has a slight impact on the magnetic properties of Gd and a high magnetic entropy change is retained in the composites. This work provides a universal approach to fabricating thermo‐electro‐magnetic materials with excellent MC and TE properties.

Oxygen Release Suppression and Electronic Conductivity Enhancement for High Performance Li‐ and Mn‐Rich Layered Oxides Cathodes by Chalcogenide Redox Couple and Oxygen Vacancy Generations

AbstractLi‐ and Mn‐rich layered oxides (LMROs) are promising cathode materials for next‐generation lithium‐ion batteries (LIBs) due to their high capacity and high energy density. However, they suffer from severe capacity and voltage fading during cycling, where the irreversible oxygen release during cycle is deemed to a severe factor. Herein, this put forward a general oxygen release suppression strategy by introducing small amounts of sodium chalcogenides during cathode slurry preparation. The formed unstable surface peroxide ions O22− of LMRO during charging is reduced to stable O2− by chalcogen ion and couples the formation of sodium chalcogenic oxides, which is reduced to sodium chalcogenides and O2− during discharging. As a result, the oxygen release is significantly suppressed and the structural stability of LMRO is greatly enhanced. Meanwhile, abundant surface oxygen vacancies are generated coupling with evidently increased carrier concentration and mobility, thus enhancing electronic conductivity significantly. The Li1.2Ni0.13Co0.13Mn0.54O2 cathode with 3 wt% Na2Se shows a capacity retention as high as 96.2% and a capacity of 225 mAh g−1 after 500 cycles at 1 C, coupling with a high capacity of 135 mAh g−1 at 10 C. The relevant mechanism for the improved electrochemical properties is revealed, which is hopefully helpful for novel strategy design to high‐performance LMRO cathodes.

Realizing an ultralow thermal conductivity via interfacial scattering and rational-electronic band reformation in p-type Mg3Sb2

Eco-friendly Magnesium antimonide (Mg3Sb2) has been extensively investigated as a promising and low-toxic thermoelectric material for intermediate (500–900 K) thermoelectric applications. Herein, p-type Zn-incorporated Mg3Sb2 was prepared by hot press technique, and its thermoelectric transport properties were investigated. The formation of Mg3−xZnxSb2 solid-solution plays a significant role in enhancing electrical conductivity of 34.59 S cm−1 due to the increased carrier concentration and reduced energy gap. Reduction in lattice thermal conductivity of 0.46 W m−1 K−1 at 753 K was obtained for Mg3−xZnxSb2 (x = 0.15) by combined scattering effect of dislocations, lattice strain, and interfaces, which is clearly seen in HR-TEM and strain analysis. These favorable conditions lead to an enhanced thermoelectric figure-of-merit (zT) of 0.25 at 753 K, which is 400% improved compared to the pure Mg3Sb2 sample.

Exploring the synergistic effects of aluminum and hydrogen impurities on high-electron-mobility sputtered-ZnO thin films

This study investigated the influence of aluminum (Al) impurity on the lattice structure, electrical, and optical properties of ZnO thin films, which were sputtered under a high vacuum environment using argon and hydrogen gases. The results revealed high electron mobility (μ) alongside a significant increase in carrier concentration (n), which deviates from the behavior typically observed in semiconductor materials. Particularly in conventional semiconductors, within the n range of 1020 cm−3, the μ exhibits a dramatic decrease with even a small increase in n. Interestingly, in this study, despite the increase in n from 2 to 3.8 × 1020 cm−3, the μ remains consistently high at around 53 cm2/Vs. Additionally, this study reveals that at an appropriate concentration, Al serves not only as a substitute for Zn to generate electrons but also as a defect passivator, similar to hydrogen. The synergistic effect of Al and hydrogen also relaxes the crystal structure, minimizing deformation and enhancing electron mobility. These effects contribute to low resistivity alongside the inherent high optical transmittance of ZnO thin films, resulting in a significantly improved figure of merit.

Non-destructive tuning of thermoelectric power factor of ZnO by surface-confined optical gating

We have studied the complex relationship between the thermoelectric properties of Zinc Oxide (ZnO) thin films and their interaction with various atmospheric conditions and ultraviolet (UV) illumination. We focused on the dynamic changes in the Seebeck coefficient (SC) and conductivity of ZnO under varied environments, which are crucial for tuning the thermoelectric power factor (PF). ZnO films showed pronounced variations in their carrier concentration and mobility when exposed to UV light in air and argon atmospheres, which can be attributed to the interplay of oxygen adsorption and desorption on the ZnO surface. The profound effect of the oxygen interaction, evidenced in a depletion layer wider than the ZnO film itself, significantly changed the electron concentration, and affected the surface conductivity and thus, the thermoelectric PF of ZnO. The experiments revealed that the SC decreased with increasing carrier concentration and mobility under UV illumination, while the thermoelectric PF increased in both atmospheres, providing pivotal insights into the nondestructive optimization of the thermoelectric properties of ZnO through controlled surface-sensitive reactions and optical gating.