Hole Concentration Research Articles

Effects of Cp2Mg molar flow rate on structural, optical, and electrical properties of semipolar Mg-doped p-AlGaN epi-layers

The semipolar (11 2‾ 2) plane Mg-doped p-Al0.42Ga0.58N epi-layers were successfully deposited on (10 1‾ 0) m-plane sapphire substrates with metal organic chemical vapor deposition technology. The effects of Cp2Mg molar flow rate on the structural, optical, and electrical properties of p-Al0.42Ga0.58N epitaxial layer were extensively studied. The randomly distributed Mg atoms and/or clusters that partially covered the growth surface were verified to act as an island-like mask to block the propagation of dislocations along the growth direction, resulting in a significant improvement in the crystalline quality of the semipolar Mg-doped p-AlGaN epi-layers. Moreover, two emission peaks with novel behavior were observed in the photoluminescence spectrum and identified to be originated from the transition between the conduction band and the Mg-related shallow acceptor energy level, and the deep Mg-induced compensation donor and the Mg acceptor pair-related transition, respectively. In addition, a hole concentration as high as 1.03 × 1017 cm−3 and a resistivity as low as 12.8 Ω cm were achieved for the semipolar Mg-doped p-Al0.42Ga0.58N epi-layer grown with the optimized Cp2Mg molar flow rate in this study.

Epitaxial analysis of GaInP/AlGaInP red light-emitting diodes with ternary AlGaP quantum barriers for quantum efficiency enhancement

Abstract We have numerically analyzed Gallium Indium Phosphide (GaInP)/Aluminum Gallium Indium Phosphide (AlGaInP) red light-emitting diodes (LEDs) by utilizing ternary Aluminum Gallium Phosphide (AlGaP) quantum barriers instead of the conventional quaternary AlGaInP quantum barriers. The simulation findings show that the use of AlGaP quantum barriers in AlGaInP red light-emitting diodes leads to a significant increase in both electron and hole concentration in the quantum wells which in turn enhances the rate of radiative recombination compared to conventional (reference) red light-emitting diodes. Furthermore, the proposed LEDs have a substantial decline in efficiency droop from 38% to 32%.

Effect of pre-strain on microstructure evolution and fracture behavior of undermatching X80 pipeline steel girth weld

This work aims to study the effect of pre-strain on the fracture behavior of X80 pipeline girth weld joint, a comprehensive analysis was conducted on the microstructure and mechanical properties of the girth weld before and after pre-strain treatment. The mechanical properties were evaluated through tensile testing, Charpy impact testing, and digital image correlation (DIC) strain analysis. Furthermore, the microstructure and fracture morphology of the girth weld were observed using optical electron microscopy (OM) and scanning electron microscopy (SEM). The results show that the application of pre-strain treatment leads to dislocation accumulation at the grain boundary of X80 pipeline girth weld, resulting in stress concentration and subsequent formation of damage holes. This process disrupts the continuity of chain M-A island and initiates small cracks at the grain boundary, ultimately causing a significant decrease in impact toughness and impact work from 177 J to about 10 J.

A kinetics-based approach to the steady state and impedance response of photoelectrodes

A kinetics-based analytical model is developed to describe the steady state and impedance response of photoelectrodes in the case where charge carrier build-up modifies the potential distribution across the semiconductor-electrolyte junction. The predictions of the steady state model are compared with numerical calculations. It is shown that carrier build up should accelerate interfacial hole transfer by increasing the potential drop across the Helmholtz layer. This effect may explain observations of higher reaction orders with respect to hole concentration during photoelectrochemical oxygen evolution. The analytical model is extended to photoelectrochemical impedance spectroscopy (PEIS). The calculations indicate that interpretation of PEIS measurements becomes more complicated if high illumination intensities are used. The modelling of the analytically calculated PEIS response using equivalent circuits is discussed with the aim of understanding the physical significance of the resistive and capacitive elements.

Understanding the origin of the high thermoelectric figure of merit of Zintl-phase KCaBi.

Herein, we have investigated the unexplored thermoelectric properties of Zintl-phase KCaBi using first-principles calculation and the solution of the Boltzmann transport equation. KCaBi shows intrinsically very low lattice thermal conductivities (κl) along the (x(y), and z)-directions of (1.78, 0.68) and (1.15, 0.43) W m-1 K-1 at 300 and 800 K, respectively. Along with the effect of very low κl, the high figure of merit (ZT) for p-type KCaBi results from the high Seebeck coefficients (S) and optimal electrical conductivities (σ), which originate from the high and steep total density of state (TDOS) at the valence band edge and the less dispersed multi-valley nature of the valence band edge in the band structure. On the other hand, large ZT for n-type KCaBi results from moderate S and high σ caused by the sloped TDOS at the conduction band edge and the highly dispersed nature of the conduction band edge in the band structure, and very low values of κl. The highest ZT of KCaBi that we obtained at 800 K along the (x(y), and z)-directions was (1.83, 0.80) for the p-type case at a hole concentration of 1021 cm-3 and (1.36, 1.22) for the n-type case at electron concentration 7 × 1018 cm-3. Our study demonstrates that both p-type and n-type KCaBi have the potential to be promising thermoelectric materials.

Effects of compressive stress on wave Love waves propagation in a piezoelectric semiconductor ZnO/Diamond: A screening effect

The issue of applied stress in hetero-structures is a persistent problem in materials science and technology. Significant efforts have been made from both numerical and experimental points of view to gain a better understanding of how to address this issue in various engineering industrial applications. In this paper, we numerically calculate the effects of compressive stress on Love waves propagation in a pre-stressed piezoelectric semiconductor ZnO/Diamond. The p-type semiconductor is explicitly taken into account, where the concentrations of holes and electrons are p0 = 1 × 1024m−3and n0 = 1 × 1023m−3, respectively. Numerical results show that the phase velocities of Love waves decrease with uniaxial stress equal to -100 MPa. In addition, this uniaxial compressive stress contributes to a decrease in the magnitude of the electric potential and the concentrations of holes and electrons. In the meantime, the “Screening effect” remains similar for both the unstressed and the pre-stressed structures.

Syntheses, crystal structures, and physical properties of non-centrosymmetric MgIn2Te4 and MnIn2Te4

In this study, we prepared two ternary tellurides, MgIn2Te4 and MnIn2Te4 (single crystals and bulk polycrystalline phases), by directly fusing the elements at high temperatures using the sealed tube synthesis method. Single crystal X-ray diffraction studies confirmed the non-centrosymmetric tetragonal structures (space group: I4‾ 2m) of the MgIn2Te4 and MnIn2Te4 phases with two formula units (Z = 2). Interestingly, the refined unit cell lengths of a = b = 6.2149(5) Å and c = 12.4240(19) Å for the MgIn2Te4 are slightly longer than those of the MnIn2Te4 structure (a = b = 6.1901(3) Å and c = 12.3877(7) Å). The asymmetric unit of these two MIn2Te4 (M = Mg and Mn) isostructural compounds contains three crystallographically independent sites: two disordered metal sites (M1/In1, M2/In2) and one Te1 site. Each metal atom in these structures is tetrahedrally coordinated with four Te1 atoms. Optical absorption studies for polycrystalline MgIn2Te4 and MnIn2Te4 samples showed bandgaps of 1.1(2) eV and 0.9(2) eV, respectively, consistent with these powders' black color. Seebeck studies confirm that holes are the majority of charge carriers for the MgIn2Te4 sample. The thermal conductivity (ktot) studies of the samples reveal ultralow values at 773 K: 0.37 Wm−1K−1 for the MgIn2Te4 and 0.44 Wm−1K−1 for the MnIn2Te4. Magnetic studies on the polycrystalline MnIn2Te4 show a paramagnetic behavior with a magnetic moment of 5.73 μB. Our theoretical studies indicate the possibility of achieving a high thermoelectric figure of merit (zT > 1.5) by optimizing the hole concentration in the MgIn2Te4 sample.

Thickness and Mg doping of graded AlGaN layers: Influence on contact layer's structural and electrical properties for DUV emitters

One of the methods to improve p-doping properties in (Al)GaN-based materials is using a technique called polarization doping. In our study, two sets of p-AlGaN contact layers with different thicknesses of the graded layer were deposited by metalorganic vapor phase epitaxy. The grown samples were investigated by atomic force microscopy, secondary ion mass spectrometry, X-ray diffraction and Hall effect measurements to study the influence of the thickness of the graded Al0.6→0Ga0.4→1N:Mg layer on the structural and the electrical properties of the whole grown structure. Additionally, theoretical calculations for the contact structures with different thicknesses of the p-Al0.6→0Ga0.4→1N graded layer were performed. The obtained results show that the concentration of p-type carriers on the p-GaN/p-AlGaN gradient interface decreases with increasing thickness of the graded layer. Our findings reveal that among the graded structures the highest concentration of holes, 1.2 × 1018 cm−3, was obtained for a structure with 50-nm-thick graded layer, while maintaining low sample resistivity. In addition, it was also shown that non-doping of the graded layer allows to improve electrical properties.

Ion implantation induced p-type conductivity in FeS2 thin film

In pursuing sustainable energy solutions, thin-film solar cells based on the Copper zinc tin sulfide (CZTS) absorber material have garnered significant attention due to their earth-abundant and non-toxic composition. However, the modest efficiency demonstrated by CZTS solar cells has prompted researchers to investigate novel approaches to improve their performance. An area of potential advancement entails the integration of appropriate hole transport layers (HTLs). In this simulation-based study, we focused on FeS2 as a highly promising candidate for use as an HTL in CZTS-based solar cells. FeS2, traditionally considered n-type, was tailored to achieve p-type conductivity through the negative ion implantation (O, P, and As) process. 40 keV ion beam was utilized, with three doses (105, 1010, 1015 cm−2) applied for each ion beam. We demonstrate successful p-type doping of FeS2 with a hole concentration of ∼1020 cm−3 in case of 1015 cm−2 dose, paving the way for its integration as an effective HTL within the CZTS solar cell structure.

Selenium alloyed tellurium oxide for amorphous p-channel transistors.

Compared to polycrystalline semiconductors, amorphous semiconductors offer inherent cost-effective, simplicity, and uniform manufacturing. Traditional amorphous hydrogenated Si falls short in electrical properties, necessitating the exploration of new materials. The creation of high-mobility amorphous n-type metal oxides, such as a-InGaZnO1, and their integration into thin-film transistors (TFTs) have propelled advancements in modern large-area electronics and new-generation displays2-8. However, finding comparable p-type counterparts poses significant challenges, impeding the progress of complementary metal-oxide-semiconductor (CMOS) technology and integrated circuits9-11. Here, we introduce a pioneering design strategy for amorphous p-type semiconductors, incorporating high-mobility tellurium within an amorphous tellurium sub-oxide matrix, and demonstrate its utility in high-performance, stable p-channel TFTs, and complementary circuits. Theoretical analysis unveils a delocalised valence band from tellurium 5p bands with shallow acceptor states, enabling excess hole doping and transport. Selenium alloying suppresses hole concentrations and facilitates the p orbital connectivity, realising high-performance p-channel TFTs with an average field-effect hole mobility of ~15 cm2 V-1 s-1 and on/off current ratios of 106 ~ 107, along with wafer-scale uniformity and long-term stabilities under bias stress and ambient aging. This study represents a crucial stride towards establishing commercially viable amorphous p-channel TFT technology and complementary electronics in a low-cost and industry-compatible manner.

The Effects of a Gate Bias Condition on 1.2 kV SiC MOSFETs during Irradiating Gamma-Radiation.

We investigated the effects of gate bias regarding the degradation of electrical characteristics during gamma irradiation. Moreover, we observed the punch through failure of 1.2 kV rated commercial Silicon Carbide (SiC) Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) due to the influence of gate bias. In addition, the threshold voltage (VT) and on-resistance (Ron) of the SiC MOSFETs decreased significantly by the influence of gate bias during gamma irradiation. We extracted the concentration of carriers and fixed charge (QF) in oxide using N-type SiC MOS capacitors and Transmission Line Measurement (TLM) patterns to analyze the effects of gamma irradiation. The Total Ionizing Dose (TID) effect caused by high-energy gamma-ray irradiation resulted in an increase in the concentration of holes and QF in both SiC and oxide. To analyze the phenomenon for increment of hole concentration in the device under gate bias, we extracted the subthreshold swing of SiC MOSFETs and verified the origin of TID effects accelerated by the gate bias. The QF and doping concentration of p-well values extracted from the experiments were used in TCAD simulations (version 2022.03) of the planar SiC MOSFET. As a result of analyzing the energy band diagram at the channel region of 1.2 kV SiC MOSFETs, it was verified that punch-through can occur in 1.2 kV SiC MOSFETs when the gate bias is applied, as the TID effect is accelerated by the gate bias.

Facile surfactant-free microwave-assisted solvothermal synthesis of Cu2Te1−xSx with enhanced thermoelectric performance

Cu2Te-based compounds show promise for thermoelectric applications, but their synthesis typically involves ball milling or melting-annealing processes. Here, we present a surfactant-free microwave-assisted solvothermal method for the controlled synthesis of Cu2Te1−xSx (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) nanostructures at 503K within just 30minutes. The substitution of sulfur promotes the formation of a hexagonal structure in Cu2Te1−xSx with x of 0.2 – 0.5, and inhibits phase transitions during heating. Moreover, the alloying of sulfur contributes to a reduction in hole concentrations toward the optimal range, resulting in enhanced power factors (e.g., 910 μW m−1 K−2 at 825K for Cu2Te0.9S0.1) and reduced thermal conductivity (e.g., 0.53Wm−1 K−1 at 825K for Cu2Te0.5S0.5). Ultimately, Cu2Te0.5S0.5 achieves a maximum dimensionless figure of merit of 0.80 at 825K. This study offers a controllable solution-based strategy for synthesizing Cu2Te-based materials with tunable compositions and enhanced thermoelectric performance.

Realizing high conversion efficiency in all-ZrCoSb-based half-Heusler thermoelectric power generators

ZrCoSb-based thermoelectric materials exhibit promising potential for power generation applications due to their high performance in both p- and n-type constituents. In this work, a newly developed all-ZrCoSb-based module achieves a maximum conversion efficiency of ∼9.3% at a temperature difference of 668 K. This high conversion efficiency is enabled by the enhanced average thermoelectric properties for both types of ZrCoSb-based materials via Bi alloying and Sn/Ni doping. The hole and electron carrier concentrations were tuned to match the theoretically predicted optimized values, contributing to high weight mobility and power factor. Additionally, the increased mass and strain field fluctuations enhance point defect scattering, leading to a significant reduction in the lattice thermal conductivity of ZrCoSb. Consequently, peak zT values of ∼1.2 and ∼1.0 at 973 K were respectively obtained in p-type ZrCo(Sb0.5Bi0.5)0.85Sn0.15 and n-type ZrCo0.85Ni0.15Sb0.5Bi0.5, resulting in high average zT values of ∼0.75 and ∼0.51 in the temperature of 300 to 973 K. This work underscores the significant potential of all-ZrCoSb-based half-Heuslers in waste heat recovery.

Construction of highly active photocatalytic interfaces through light field modulation and photo-deposition of Pd sites

Anchoring noble metal sites through photo-reduction is an effective way to modulate charge distribution on photocatalytic interfaces, thereby enhancing photocatalytic performance. The irradiation field on the exposed surfaces of photocatalysts has an important influence on the morphology and distribution of noble metal sites. However, non-uniform light field derived from the scattering effects of particle-form photocatalysts hinders the well-distributed photo-deposition of noble metal sites. To address this challenge, we proposed a photo-deposition method utilizing the optical fiber coated with photocatalysts. TiO2 nanorod (NR) array was coated on the optical fiber to achieve a well-distributed irradiation filed across the NR array. This resulted in a concentration of the irradiation field primarily within the NR array, maintaining uniformly distributed light intensities throughout. Palladium (Pd) sites dominated by nanoclusters were well distributed on TiO2 NR array utilizing a photo-reduction method. These Pd sites functioned as electron acceptors, facilitating the effective separation and transfer of photo-generated carriers. Consequently, an highly active photocatalytic reaction interface was constructed, demonstrating the accumulation of a substantial concentration of holes and their efficient conversion into hydroxyl radicals (·OH). Notably, hydroxyl radicals with a concentration of 62.6 μM could be generated within 14.4 min. The construction of this efficient photocatalytic interface offers an optimal platform for accelerating photocatalytic reactions and enhancing photocatalytic efficiency.

Surface-enhanced p-type transparent conducting CuI−Ga2O3 films with high hole transport performance and stability

CuI is a wide bandgap p-type transparent conductor with promising optoelectronic properties. However, conventional CuI films prepared through the iodination of Cu films exhibit rough surface, poor stability and excessively high hole concentration, hindering its application. Herein, we introduce CuI−Ga2O3 composite films as a substitution to overcome the shortcomings of pure CuI. During the iodination process, Ga2O3 hindered the mobility of CuI grain boundaries, resulting in small grain size and low surface roughness. After the charge re-equilibrium and low-energy carrier filtering at the interface between Ga2O3 and CuI, the hole concentration in the films decreased by an order of magnitude. Due to the interface effect of Ga2O3 at the grain boundaries of CuI, the hole mobility increased by 5 times, and the conductivity improved by 53%. The ultra-wide band gap of Ga2O3 enhanced the transmittance of CuI films in short wavelength region. Ga2O3 served to passivate the grain boundaries of CuI, preventing the oxidation of CuI and the loss of iodine, consequently improving the stability of the films. This work will deepen the understanding of the failure and hole transport mechanisms of CuI films.

Anodic Reconstructed p+-GaAs/a-InAsN for Stable and Efficient Photoelectrochemical Hydrogen Evolution.

The extremely poor solution stability and massive carrier recombination have seriously prevented III-V semiconductor nanomaterials from efficient and stable hydrogen production. In this work, an anodic reconstruction strategy based on group III-V active semiconductors is proposed for the first time, resulting in 19-times photo-gain. What matters most is that the device after anodic reconstruction shows very superior stability under the protracted photoelectrochemical (PEC) test over 8100s, while the final photocurrent density does not decrease but rather increases by 63.15%. Using the experiment and DFT theoretical calculation, the anodic reconstruction mechanism is elucidated: through the oxidation of indium clusters and the migration of arsenic atoms, the reconstruction formed p+-GaAs/a-InAsN. The hole concentration of the former is increased by 10 times (5.64×1018cm-1 increases up to 5.95×1019cm-1) and the band gap of the latter one is reduced to a semi-metallic state, greatly strengthening the driving force of PEC water splitting. This work turns waste into treasure, transferring the solution instability into better efficiency.

Dual Alloying Enables High Thermoelectric Performance in AgSbTe2 by Manipulating Carrier Transport Behavior

AbstractAgSbTe2 exhibits superior thermoelectric performance in the mid‐temperature region, but its electrical properties are strongly affected by intrinsic defects and secondary phases. Distinctively, the high mobility electrons still play an important role as minority carriers in p‐type AgSbTe2 even below the bipolarization temperature and decrease the Seebeck coefficient. Here, the Al and Se dual alloying can effectively increase the hole concentration by reducing the cation vacancy formation energy and simultaneously reduce the electron concentration by suppressing the n‐type Ag2Te secondary phase are demonstrated, which results in the shift of carrier transport from two‐type to one‐type as confirmed by Hall measurement. Consequently, through adjusting the ratio of hole and electron conductivity, the average power factor of alloyed sample is enhanced by 70%. Combined with further reduced lattice thermal conductivity resulting from high‐density stacking faults and superstructures, a maximum zT of 1.90 and an average zT of 1.42 are obtained in the temperature range of 323 to 623 K in the (AgSbTe2)0.98(AgAlSe2)0.02 sample. Finally, based on the finite element analysis modeling results, both single‐leg and double‐leg thermoelectric devices are fabricated, which show high conversion efficiency of 11.2% and 5.2%, respectively.

Experimental determination of the band offsets at the UWBG p-LiGa5O8/Ga2O3 interface

LiGa5O8, a recently discovered ultrawide bandgap semiconductor exhibiting p-type conductivity at room temperature, is grown on (010) β-Ga2O3 substrate. Utilizing a mist chemical vapor deposition method, LiGa5O8 thin film grown on insulating Ga2O3 substrate exhibits hole concentration ∼2.31 × 1018 cm−3 and hole mobility ∼2.07 cm2/V s. The resulting heterostructure is characterized comprehensively. A smooth, uniform film growth was observed by scanning electron microscopy and atomic force microscopy imaging. Cross-sectional scanning transmission electron microscopy and x-ray diffraction confirm the growth of spinel cubic crystal structure of LiGa5O8 along the [110] direction. Moreover, the valence and conduction band offsets at p-LiGa5O8/β-Ga2O3 heterointerface were determined via x-ray photoelectron spectroscopy. The determined band alignments at LiGa5O8/β-Ga2O3 interface reveal the formation of a type-II (staggered) heterojunction. The experimental measurements provide valuable parameters of the band offsets at the heterointerface, addressing a crucial aspect for future power electronic device design and fabrication based on β-Ga2O3 ultrawide bandgap semiconductors.

Study on activation of fluorogypsum by sodium sulfate and sodium nitrite

Given the issues related to poor hydration activity, long setting time and low early strength of industrial by-product fluorogypsum (FG), the composite modifiers (Na2SO4 and NaNO2) were utilized to enhance its reactivity. The investigation of the mechanism involved the utilization of contemporary analytical methods, including X-ray diffraction (XRD), 1H low-field nuclear magnetic resonance (NMR), and Scanning electron microscope and Energy Dispersive Spectrometer (SEM-EDS). The results demonstrated that the incorporation of modifiers significantly enhanced both the hydration rate and activity of fluorogypsum. The optimum concentration of the composite modifier was found to be 1.5 wt% Na2SO4 and 0.5 wt% NaNO2. The addition of modifiers (1.5 wt% Na2SO4 and 0.5 wt% NaNO2) significantly shortens the setting time of FG paste, reducing it by approximately 500 min compared to the control sample. After 28 days of curing, the flexural strength and compressive strength of the fluorogypsum sample containing modifiers (1.5 wt% Na2SO4 and 0.5 wt% NaNO2) increased by 55.5 % (reaching 4.2 MPa) and 31.5 % (reaching 37.6 MPa), respectively. The modifiers facilitate the transformation from anhydrite (CaSO4, AH) to dihydrate gypsum (CaSO4·2H2O, DH). Both NaNO2 and Na2SO4 alter the growth rates of different crystal axes during DH crystal growth, transforming them into prismatic and needle-shaped DH. The prismatic and needle-shaped DH crystals were arranged in layers, resulting in a compact structure with low hole content and few pores, which led to increased density of the hardened paste and higher strength. The current study provides evidence that the inclusion of composite modifiers greatly improves the activity of FG, making it more efficient in the field of building materials.

The effect of porous silicon thickness and pore size on the electrical properties of TiO2/PS heterojunctions

Heterojunctions made by depositing Titanium dioxide (TiO2) on porous silicon using the sol-gel method were electrically characterized. It was found that charge transfer mechanisms are dependent on the porosity and layer thickness, as well as the pore size. For the case of devices fabricated in mesoporous matrix, the current-potential curve appears like a Schottky ohmic contact, associated with the predominance of the tunneling charge transfer mechanism, depicting a reduction in current intensity as the meso-PS thickness increases. This behavior was related to the increase of TiO2 into the pores, which in turn leads to the hole concentration decrease from around 1020 to 1012 cm−3 because the compensation effect, as revealed by the Mott-Schottky analysis, while the impedance analysis shows that this reduction in holes is traduced as increase of the resistance associated with each interface. In the case of the devices yielded in macroporous layers, it was found that devices with thinner layers behaves as hole-blocking device or even as ohmic contact, depending on the amount of interface states. In addition, in hole blocking devices, the presence of at least two diodes with opposite behavior is marked.