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A graded composition superlattice structure is proposed by combining simulation with experimentation. The structural factors affecting graded symmetric superlattices and graded asymmetric superlattices and their action modes are simulated and analyzed. A Mg-doped graded symmetric superlattice structure with high Al content, excellent structural quality, good surface morphology and excellent electrical properties was grown by MOCVD equipment. The AlxGa1−xN superlattice with Al composition of 0.7 in the barrier exhibits a hole concentration of approximately 5 × 1015 cm−3 and a resistivity of 66 Ω·cm. [ABSTRACT FROM AUTHOR]

A graded composition superlattice structure is proposed by combining simulation with experimentation. The structural factors affecting graded symmetric superlattices and graded asymmetric superlattices and their action modes are simulated and analyzed. A Mg-doped graded symmetric superlattice structure with high Al content, excellent structural quality, good surface morphology and excellent electrical properties was grown by MOCVD equipment. The AlxGa1−xN superlattice with Al composition of 0.7 in the barrier exhibits a hole concentration of approximately 5 × 1015 cm−3 and a resistivity of 66 Ω·cm.

This study discusses the conditions for the occurrence of two-dimensional superconductivity under the action of an electric field on an La2 – xSrxCuO4 plate at a temperature lower than the maximum temperature of the superconducting transition, but when the concentration of charge carriers falls outside the superconductivity range. The study is carried out for a lanthanum-strontium cuprate plate at various hole concentrations, as well as temperature, and potential differences. A quasi-two-dimensional superconducting layer arises near the surface of the plate. The thickness of the superconducting layer is several angstroms and independent of the field strength in the range investigated. The thickness depends only on the concentration of holes and temperature. In addition, the distance of the superconducting layer from the edge of the plate is found to be a function of all three factors. The conditions used for conducting the experiment are also formulated. [ABSTRACT FROM AUTHOR]

TiO 2 doping content affects the critical temperature (T c) and the variations of local structure on Bi 1.6 Pb 0.4 Sr 2 Ca 2 Cu 3 O 10+δ. The (Bi 1.6 Pb 0.4 Sr 2 Ca 2 Cu 3 O 10+δ) 1-x (TiO 2) x samples were fabricated with the solid-state reaction process, where x = 0, 0.002, 0.004, 0.006, 0.008, and 0.01. The T c values of the samples were obtained by measuring resistivity versus temperature, indicating that T c gradually decreased with increasing doping content (x). To explain the obtained degradation of T c , carrier properties, role of interlayer coupling, and local structure were systematically investigated using Azlamozov–Larkin theory and its Lawrence–Doniach modification for strong anisotropic superconductors. The calculation of excess conductivity at the mean field region showed that the c-axis coherence length (ξ c) and the effective inter-layering spacing (d) increased with increasing doping content. X-ray diffraction patterns also showed that the bond distances increased with increasing TiO 2 content. The copper valence (V) and carrier concentration (p) of the samples were determined by analyzing the Cu L 2,3 -edge X-ray absorption near edge structure spectra. The values of V and p showed the same trend of decreasing with increasing x. A close correlation between the changes in local structure parameters and degradation of T c of (Bi 1.6 Pb 0.4 Sr 2 Ca 2 Cu 3 O 10+δ) 1-x (TiO 2) x was then probably concluded. [ABSTRACT FROM AUTHOR]

In this paper, a SOI MOSFET is proposed using a P-N structure and an electrically hole-free region (EHFR-SOI). In this structure, to improve the electrical characteristics such as short channel effects, self-heating effects, and floating body effects, a Si3N4 layer is used on the source side of the SOI MOSFET with a P-N structure. The proposed technique converts the P-N structure to a N-P-N structure by creating an electrically hole-free region. So, by reducing the applied electric field to the carriers, a significant reduction in the electron temperature of the device will be created. Simulations and studies of the structure show that its thermal behavior is significantly improved. Also, the floating body effect, effective mobility, hot electron effect, and electric field in the structure are enhanced compared to a conventional SOI (C-SOI) structure. In addition, the gate-source and gate-drain capacitors have been improved, which indicates a higher switching speed of the structure. [ABSTRACT FROM AUTHOR]

In this paper, we present the dependence of source resistance sensibility on the gate bias effect in a High Electron Mobility Transistor (HEMT) using the Drift-Diffus (D-D) model with the SILVACO Technology Computer-Aided Design (TCAD) tool. The obtained results show that the increases of gate bias effect on substrate lead to decreasing the source resistance of the simulated device. The reported increase in the effect of gate induces the increases of transferred holes concentration towards the source region and which induce the decreases of source resistance. The decrease of source resistance can also be made by reducing the buffer thickness which leads to an increase in the gate effect on the substrate. The source resistance value is influenced by the Drain-Induced Barrier Lowering (DIBL) effect where the rate of decreasing the source resistance will be decreasing consequently to increase the drain bias. The reduction of the source resistance induces the increase of device sensibility for lows values of current.

Semimetal electrodes for 2D semiconductors have been extensively studied; however, research on p-type semimetals has been limited due to the scarcity of materials that satisfy both high work functions and low resistances. In response, we investigated the behavior of NiSe 2 as an electrode. Utilizing a novel co-evaporation method that suppresses oxidation and contamination, we synthesized NiSe 2 demonstrating a high work function of 5.53 eV, a low resistance of 5.81 × 10 -5 Ω cm, and a record hole concentration exceeding 10 23 cm -3 . We confirmed that when WSe 2 comes into contact with NiSe 2 , the Fermi level of WSe 2 falls below the work function of NiSe 2 , leading to complete hole degeneration of the channel. This unusual Fermi level alignment correlates with the high hole concentration in NiSe 2 and the maximum energy level of its hole pockets. Our research provides new insights into how an electrode's hole concentration affects channel behavior.

In this paper, we present the dependence of source resistance sensibility on the gate bias effect in a High Electron Mobility Transistor (HEMT) using the Drift-Diffus (D-D) model with the SILVACO Technology Computer-Aided Design (TCAD) tool. The obtained results show that the increases of gate bias effect on substrate lead to decreasing the source resistance of the simulated device. The reported increase in the effect of gate induces the increases of transferred holes concentration towards the source region and which induce the decreases of source resistance. The decrease of source resistance can also be made by reducing the buffer thickness which leads to an increase in the gate effect on the substrate. The source resistance value is influenced by the Drain-Induced Barrier Lowering (DIBL) effect where the rate of decreasing the source resistance will be decreasing consequently to increase the drain bias. The reduction of the source resistance induces the increase of device sensibility for lows values of current. [ABSTRACT FROM AUTHOR]

The introduction of heterovalent Al3+ doping has been found to enhance the electrical properties of semiconducting Cu 2 ZnSnS 4 thin films. However, the impact of the Al substitution site on the properties of Cu 2 ZnSnS 4 thin films remains ambiguous. In this study, we employed a sputtering technique to deposit Cu–Zn–Sn–Al stacked metal precursors. Subsequent sulfurization treatment was carried out to yield the final Al-doped Cu 2 ZnSnS 4 thin films. Structural and compositional measurements revealed that the substitution site of Al can be tailored by adjusting the metal composition and stacked order of the precursor. The anticipated substitution sites for Al dopants in Cu, Zn, and Sn positions facilitated the growth and crystallization of Cu 2 ZnSnS 4 thin films. Notably, the chemical valence of Al remained in the +3 state regardless of the specific substitution site. Furthermore, the hole concentration in thin films doped with Al at Cu and Zn sites is lower compared to those doped at the Sn site. All Al-doped thin films exhibited a widened band gap and improved photoluminescence properties relative to the un-doped thin film. Remarkably, among the fabricated samples, the Al-doped Cu 2 ZnSnS 4 sample with reduced Sn thickness demonstrated the best crystallinity, the highest hole concentration, the largest absorption coefficient, and the strongest photoluminescence peak. These results suggest that the most favorable substitution site for Al in Cu 2 ZnSnS 4 thin films is the Sn position. This work offers a deeper understanding of the Al-doping mechanism in Cu 2 ZnSnS 4 thin films. • The substitution site of Al in Cu 2 ZnSnS 4 was modulated by the intrinsic element ratio and the layered sequence of precursor. • Independent of the substitution site, Al-doping enhances the hole concentration in Cu 2 ZnSnS 4. • Substituting Sn with Al results in the optimal crystallinity and the highest hole concentration in Cu 2 ZnSnS 4. • The substitution site of Sn is the most advantageous for Al-doping in Cu 2 ZnSnS 4. [ABSTRACT FROM AUTHOR]

In this letter, novel heterostructure p-i-n GaN avalanche photodiodes (APDs) with p-type In0.05Ga0.95N layer are proposed and analyzed through Silvaco Atlas simulations. The introduction of the In0.05Ga0.95N layer generates a negative polarization charge at the p-In0.05Ga0.95N/i-GaN heterojunction interface via the piezoelectric polarization effect. Three times higher hole concentration in the p-In0.05Ga0.95N layer is obtained due to the smaller activation energy of the Mg dopant. Induced polarization charge and increased hole concentration work together to reduce the voltage drop in the p-In0.05Ga0.95N layer and enhance the electric field intensity in the i-GaN layer. The calculated results show that the heterostructure APD demonstrates a reduced operating voltage of more than 26 V and an improved multiplication gain by an order of magnitude in comparison to the conventional one.

In this work, a close correlation between variations of critical temperature (T c) and the hole concentration of (Bi 1.6 Pb 0.4 Sr 2 Ca 2 Cu 3 O 10+δ) 1-x (Fe 3 O 4) x systems was studied. The (Bi 1.6 Pb 0.4 Sr 2 Ca 2 Cu 3 O 10+δ) 1-x (Fe 3 O 4) x samples were fabricated using the solid-state reaction method, where x ranged from 0 to 0.2. The T c values of the samples deduced from magnetization versus temperature measurement gradually decreased with increasing the Fe 3 O 4 content (x). To investigate a possible reason for the observed decrease in the values of T c in the samples, the valence state of copper (V) and the hole concentration (p) in all samples were examined by analyzing the Cu K-edge and Cu L 2,3 -edge X-ray absorption near edge structure (XANES) spectra. The values of V and p monotonously decreased with the increase in Fe 3 O 4 doping content (x) and agreed with the behavior of T c. The existence of Fe3+ was confirmed by analyzing Fe L 2,3 -edge XANES. Hence, Fe3+ ions possibly entered the lattice structure of the samples and filled the holes in CuO 2 planes. The degradation of superconductivity in Fe 3 O 4 doped samples was then explained. [ABSTRACT FROM AUTHOR]

This review is on the effects of elemental substitutions at the Tl-site of TlSr 2 CaCu 2 O 7 (Tl-1212) superconductor. The objective of this paper was to determine the elements that enhance or suppress the superconducting transition temperature, T c of (Tl 1- x M x)Sr 2 CaCu 2 O 7 phase. The elements included in this review were M = Pb, Bi, Cr, V, Re, Zr, In, Er, Gd, Na, K, Rb and Se. The relations between transition temperature and the ionic radius, coordination number, valence state and optimization of the hole concentration of the selected elements were studied. The preparation methods, sintering temperature, Tl-1212 phase and structural stability were also discussed. All alkali metals (K, Na and Rb) suppressed the transition temperature of the Tl-1212 phase. The transition temperature generally decreased linearly with ionic radius except for Cr which showed the highest T c although its ionic radius is smaller. [ABSTRACT FROM AUTHOR]

An analytical model has been developed to investigate the activation energy profile in Mg-doped p-AlxGa1−xN alloy for the entire range of Al composition. For any Al content, the calculated activation energy quantitatively shows a good agreement with experimental result which has also been confirmed by both Hydrogen atom model and effective Bohr radius model. Through this empirical analysis, a breakthrough is apparent for the hole concentration and sheet resistivity with particular Al concentration. It is found that the hole concentration is < 1017 cm−3 while the Al content, x > 30% in p-AlxGa1-xN. Moreover, the sheet resistivity is found to be < 1 Ω-cm up to the Al content of 30%. Finally, the temperature-induced changing behavior of hole concentration and sheet resistivity have been explored here. These results could be a good insight for fabricating the AlGaN-based real-world devices for future optoelectronics. [ABSTRACT FROM AUTHOR]

In this letter, novel heterostructure p-i-n GaN avalanche photodiodes (APDs) with p-type In0.05Ga0.95N layer are proposed and analyzed through Silvaco Atlas simulations. The introduction of the In0.05Ga0.95N layer generates a negative polarization charge at the p-In0.05Ga0.95N/i-GaN heterojunction interface via the piezoelectric polarization effect. Three times higher hole concentration in the p-In0.05Ga0.95N layer is obtained due to the smaller activation energy of the Mg dopant. Induced polarization charge and increased hole concentration work together to reduce the voltage drop in the p-In0.05Ga0.95N layer and enhance the electric field intensity in the i-GaN layer. The calculated results show that the heterostructure APD demonstrates a reduced operating voltage of more than 26 V and an improved multiplication gain by an order of magnitude in comparison to the conventional one. [ABSTRACT FROM AUTHOR]

• The effect of Sr–substitution for Ba on superconductivity in (Yb,Ca)(Ba,Sr) 2 Cu 3 O 6 without any oxygen ions in the blocking layer of Cu(1)O chain. • T c increases with increasing Sr–content in contrast to REBa 2 Cu 3 O 7 with T c ∼90 K. • Holes are more likely supplied to the conducting Cu(2)O 2 plane than the blocking layer of Cu(1) through the Sr–substitution. • The highest T c = 73 K is greatly higher than the previous record of 50 K in (RE,Ca)Ba 2 Cu 3 O 6. We have investigated the effect of the Sr-substitution for Ba on the superconductivity in Yb 0.6 Ca 0.4 Ba 2- y Sr y Cu 3 O 6 without O chain forming the so-called Cu(1)O chain in the blocking layer. It has been found that T c increases with increasing y even though no holes are doped through the Sr2+-substitution for Ba2+. The increase in T c is because holes doped by the Ca-substitution for Yb are more likely supplied to the superconducting Cu(2)O 2 plane than the blocking layer of Cu(1) owing to the contraction of the Cu(2)O 2 plane through the substitution of smaller Sr2+ for larger Ba2+. The highest T c onset = 73 K observed for y (Sr) = 0.6 is greatly higher than the previous record of T c onset = 50 K in (RE ,Ca)Ba 2 Cu 3 O 6 (RE : rare-earth element). The reason why it is lower than ∼90 K for RE Ba 2 Cu 3 O 7 is the low hole-concentration in the Cu(2)O 2 plane. [ABSTRACT FROM AUTHOR]

This paper suggests and investigates a p-n structure, which emulates as a MOSFET. In the proposed structure we utilize an L-shape contact with a proper work function over the source region of silicon on insulator MOSFET to convert the source region from p+ to n+. We check its performance by indicating the band diagram and electron and hole concentrations which acts as n-p-n transistor in OFF state. By employing this idea, the p-n structure acts as MOSFET by a Virtual Hole's Well at the source side (VW-SOI MOSFET), so the carrier concentrations specially hole concentration modify in the channel chiefly the source side in ON state which suppresses the floating body effect. The hole concentration, electric field, floating body effect and finally the lattice temperature improve. So the self heating effect that is one of the biggest problems in SOI devices, improves. Also, the simulation results of the VW-SOI MOSFET indicate that it is a suitable case for a switching performance because of decreasing gate-source, gate-drain capacitances, and noise. And finally the proposed structure can be a reliable structure because it decreases the effect of hot carriers due to short channel effects. [ABSTRACT FROM AUTHOR]

Abstract The theoretical relationship between the hole concentration (n), electron diffusion length (L D), and surface photoelectron escape probability (P) was studied. It is found that with increase of n , L D decreases and P increases. Based on the Spicer's three-step photoemission model and the quantum efficiency (QE) formula of negative electron affinity (NEA) GaN photocathode, the theoretical relationship between n and QE could be obtained. A three-dimension graph was drawn to show the relationship between QE and photon energy (E), which allowed us to observe the QE changing with n intuitively. In the whole wavelength range, QE tended to rise firstly and then fall down. The optimal n shifted to the lower concentration with the increase in wavelength due to the deeper attenuation length of the long-wavelength light. Based on the photo-electrical response of the effective band, the optimal doping concentration of 1.26 × 1017 cm−3 was obtained. The comparison results indicated that the experimental data were consistent with the simulated curves. Highlights • Theoretical relationship of hole concentration (n) and electron diffusion length (L D), surface photoelectron escape probability (P) are studied. • Theoretical relationship of n and QE is obtained. For the whole wavelength, QE shows a trend of increasing until a peak and then decreasing with n. • The optimal n shifts to the lower concentration with the increase of wavelength, which is caused by the deeper attenuation length for the long wavelength light. • The optimal doping concentration of 1.26 × 1017 cm−3 is gotten. • The process and results of experiment prove the the correctness of our theory. [ABSTRACT FROM AUTHOR]

Cubic Ti 1−x Al x N (x = 0.5, 0.6) films were deposited using RF (radio frequency) magnetron sputtering and cathodic arc ion plating methods on a thermally oxidized Si substrate to evaluate the temperature dependence of their electrical characteristics by Hall measurements from 10 K to 295 K. The temperature dependence of the hole concentration and the electrical conductivity above about 200 K shows that cubic TiAlN in this study had semiconductor characteristics, indicating that the hole conduction in the valence band is dominant in a high temperature range above about 200 K. In contrast, the variable range hopping conduction is dominant in a low temperature range below about 100 K. In addition, the hole mobility of Ti 0.4 Al 0.6 N deposited by RF sputtering increased with increasing temperature above 220 K, even though the phonon scattering increases. This result shows that a disordered grain boundary between polycrystalline TiAlN acts as a barrier layer for the hole conduction. [ABSTRACT FROM AUTHOR]

We present a distinct approach to enhance the performance of physically doped tunnel field-effect transistors (TFETs) based on creation of a layer of positive charge at the semiconductor-insulator interface in the source region. Formation of such a hole layer resolves the issue related to material solubility and improves direct-current (DC) as well as high-frequency figures of merit. To implement this approach, a typical P+-I-N+-type physically doped TFET structure is considered. Furthermore, a metal electrode with workfunction of 4.53 eV is placed over the heavily doped P+ source region with a negative supply voltage. The negative voltage at the source electrode attracts holes from the source region and creates a hole layer just below the semiconductor-insulator interface. This phenomenon makes the source-channel junction abrupt and reduces the tunneling barrier width, resulting in higher tunneling generation rate of charge carriers at the source-channel junction. Thus, the proposed device shows 100-fold increased ON-state current and a threshold voltage reduction of 300 mV. Analog/radiofrequency (RF) parameters are also greatly improved compared with the conventional device. Furthermore, optimization of the spacer length (LSG), i.e., the gap between the source and gate electrode, and application of a negative voltage (-VSE) at the source electrode (SE), were applied to achieve the optimum performance. Moreover, device linearity was also analyzed in a comparative manner. [ABSTRACT FROM AUTHOR]

The effects of Mg-doping on the characteristics of semi-polar ( 1 1 2 ¯ 2 ) plane Al 0.15 Ga 0.85 N films grown on ( 1 0 1 ¯ 0 ) m-plane sapphire substrates with metal-organic chemical vapor deposition (MOCVD) technique were investigated intensively and systematically. The characterization results showed that the crystalline quality of the ( 1 1 2 ¯ 2 ) plane AlGaN films could be improved by optimizing the Mg-delta-doping process. Whereas, the surface morphology for the samples was monotonously degraded with increasing the Mg-doping level. Meanwhile, a hole concentration as high as 5.4 × 10 17 cm −3 were achieved by optimizing the Mg-doping level. Furthermore, the luminescence mechanism of the samples was investigated by photoluminescence spectra at room temperature. [ABSTRACT FROM AUTHOR]

Polycrystalline samples of Nd1-xPrxBa2Cu3O7-δ with 0≤x≤0.30 were made by standard solid state methods. The transport and superconducting properties were studied by the resistivity and the thermoelectric power measurements as a function of temperature and doping concentration. The resistance and the thermoelectric power were increased by increasing doping concentration. The pseudogap temperature was measured from downturn deviation in a linear dependence of resistance as a function of temperature. The resitivity, the thermoelectric power, the critical temperature, and the pseudogap temperature results suggested that the hole concentration in CuO2 planes was decreased by increasing Pr doping concentration. The resistivity and the thermoelectric power results were analyzed by the bipolaron and the phenomenological narrow band model, respectively. A good agreement between models and data was obtained. On the basis of these models, it was inferred that the localization tendency is one of the main reasons for decreasing the hole concentration in the CuO2 plane, which results in the strong depression of the superconductivity.

We have demonstrated the effect of p -GaN hole concentration on a graphene current spreading layer (CSL) for stabilization and improved performance of a near-ultraviolet light-emitting diode (NUV LED). While NUV LEDs with a more lightly-doped p -GaN showed poor electrical and optical properties and unstable performance, NUV LEDs with more heavily-doped p -GaN (∼2 × 10 17 cm −3 ) showed very stable, outstanding performance. The main factor of the improvement was the enhanced contact property between the graphene CSLs and the p -GaN that resulted from the increase of the hole concentration, which led to a thinner barrier and an enhanced current injection. From our results, we were able to determine that hole concentration as heavy as 2 × 10 17 cm −3 in p -GaN layers is a primary condition in NUV LEDs with graphene-based CSLs. [ABSTRACT FROM AUTHOR]

The Mg-delta-doped p-AlInGaN epi-layers were successfully grown on c -plane sapphire substrates by metal-organic chemical vapor deposition (MOCVD). The effects of growth temperature on the characteristics of the Mg-delta-doped p-AlInGaN epi-layers were investigated in detail with scanning electron microscopy (SEM), high resolution X-ray diffraction (HR-XRD), photoluminescence (PL), and Hall effect measurements. The characterization results showed that the surfaces of the p-AlInGaN epi-layers were textured with a high density of hexagonal pits, which was found to be strongly dependent on the growth temperature. This feature should be very helpful to enhance the light extraction efficiency when the p-AlInGaN epi-layers were used as the top p-contact layer for making AlInGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs). In addition, the low temperature PL spectra demonstrated that the Mg-H complex-related broad emission band which was observed for the as-grown p-AlInGaN epi-layer samples was not resolvable for the annealed samples. This fact implies that the Mg-H complex can be effectively dissociated by annealing process. Moreover, owing to the improved In incorporation efficiency and crystalline quality for the p-AlInGaN epi-layers, a hole concentration as high as 1.69 × 10 17 cm −3 was achieved with the reformed Mg-delta-doping technique developed in this study. [ABSTRACT FROM AUTHOR]

The effect of CpMg/Ga ratio on the properties of p-GaN was explored by scanning Hall probe, photoluminescence (PL), and atomic force microscopy measurement. It was found that p-GaN has an optimal doping concentration under 2% CpMg/Ga ratio, and higher or lower doping concentration is not beneficial to the conductivity. Hole concentration under the optimum condition is 4.2 × 10 cm at room temperature. If the CpMg/Ga ratio exceeds the optimum value of 2%, surface morphology and electrical conduction properties become poor, and blue emission at 440 nm, considered deep donor-to-acceptor pair transitions in the PL spectra, are dominant. The decrease in electrical properties indicates the existence of compensating donors because the hole concentration decreases at such high CpMg/Ga ratio. The obtained results indicate that Mg is not incorporated in the exact acceptor site under a heavy doping condition, but acts as a deep donor, instead. [ABSTRACT FROM AUTHOR]

In this study, magnetron reactive sputtering using a copper oxide target was performed to obtain a series of high-quality CuO x films with high hole concentration. The results of X-ray photoelectron spectroscopy and Hall measurements revealed that the hole concentration exhibited a negative correlation to the Cu + to Cu2+ ratio in the p-type CuO x film. This phenomenon indicated that the hole concentration can be modulated by adjusting film deposition conditions. Considering the high hole concentration and fine surface quality, these CuO x films were used as p-type gates without gate etching and positively shifted the threshold voltage (V th) of AlGaN/GaN high-electron-mobility transistors (HEMTs). This study is the first to achieve quasi-normally off GaN HEMTs using CuO x gates, in which V th positively shifted approximately 2.5 V and reached 0.5 V. Because of the excellent surface quality of the CuO x gate, the off-state current and gate leakage current of GaN HEMTs improved considerably. This study verified that CuO x is a promising gate candidate for fabricating low-cost, normally off AlGaN/GaN HEMTs. [Display omitted] • P-type CuO x gates were obtained through magnetron reactive sputtering of a copper oxide target. • For the first time, a quasi-normally off AlGaN/GaN HEMT with a CuO x gate was achieved. • The Cu+ to Cu2+ ratio in CuO x films was inversely proportional to hole concentration. • Adjustment of Cu+ :Cu2+ in CuO x gates allows the fabrication of AlGaN/GaN HEMTs with different threshold voltages. [ABSTRACT FROM AUTHOR]

Based on first-principles calculations, herein, we reveal the origin of p-type conductivity and the roles of Al and O in the enhancement of hole concentration in Sb 2 Se 3 thin films. A new class of low-energy defects with shallow acceptor levels is presented by substituting Se with O and inducing Sb vacancy [O Se –V Sb ] complex. Moreover, the concentration of holes induced by the intrinsic and extrinsic defects is calculated and discussed. Our results can explain the intriguing experimental observation where the hole concentration is enhanced after Al 2 O 3 capping and provide a new insight to the defect chemistry and physics of Sb 2 Se 3 thin films. In addition, Al 2 O 3 layers with varying thicknesses have been deposited on the surface of Sb 2 Se 3 films. The crystallinity, orientation and electrical properties of Sb 2 Se 3 films have been investigated in detail. Lastly, 6.87% efficiency of Sb 2 Se 3 solar cells without other optimization has been obtained based on the structure of FTO/CdS (CBD)/Sb 2 Se 3 /Al 2 O 3 /Au. [ABSTRACT FROM AUTHOR]

The transparency and p-type performance for B 6 P is investigated by the hybrid functional calculations. It is found that B 6 P is an indirect band gap semiconductor with a band gap of 3.23 eV. The hole effective mass along the T to Γ direction is only 0.35 m 0 , where m 0 is the mass of the free electron. The B 6 P is a promising high transparent material due to its low absorption, low reflection, and high transmittance. For intrinsic B 6 P, B P (P B(B)) is the main defect under B-rich (P -rich) condition. The formation energy of the dominant defect is calculated. The thermodynamic simulation method is performed to quantitatively study the Fermi energy, hole concentration, and defect density. Our results show that quenching the intrinsic B 6 P from 1900 K to room temperature can increase the holes' density from 9.86 × 102 to 2.80 × 1013 cm−3. These results provide essential insight for B 6 P as a potential transparent p-type material. • B 6 P is an indirect band gap semiconductor with the band gap 3.23 eV. • Hole effective mass along T-Γ direction is only 0.35 m 0 (m 0 is the mass electron). • B 6 P is high transparency for low absorption and high transmittance. • The hole concentration for B 6 P with intrinsic defects can reach 2.80 × 1013 cm−3. [ABSTRACT FROM AUTHOR]

The electron work function, hole concentration and diffusion length were compared for poly(3-hexylthiophene) polymer (P3HT) that is commonly used for construction of solar cells, and two types of native polythiophene (PT) samples which are prospective candidates for this purpose. The polythiophene samples were prepared from 2 different precursors by thermal or chemical treatment at room temperature. Cyclic voltammetry and work function measurements were used for estimating the concentration of holes. The measured data were evaluated assuming the validity of band theory based on the tight-binding model. Published data on the valence bandwidth were used for calculating the value of the overlap integral which is related to the hole effective mass. Energy band diagrams were constructed for all 3 materials. Finally, the exciton diffusion length, which is a critical parameter for the application of conjugated polymer materials in solar cells, was measured by a modified surface photovoltage method. The approach allowed us to identify the differences in the material properties related to the processing method. Morphology of the samples determined by AFM was another tool showing these differences. It is stated that a native polythiophene prepared by treatment with acids is a prospective material for solar cells and shows a similar quality as that produced by a thermal process. [ABSTRACT FROM AUTHOR]

Orthorhombic Cu 3 SnS 4 nanocrystals (NCs) possessing obvious localized surface plasmon resonances (LSPR) in the near-infrared region (NIR) frequencies are prepared. In Cu 3 SnS 4 NCs, valence state of Cu remains close to +1, indicating Cu + occupies positions originally belong to Cu 2+ in a similar way as Cu + replaces Zn 2+ to form Cu Zn antisites in Cu 2 ZnSnS 4 . The increase of Cu/Sn ratio results in slightly red-shifted and weakened NIR absorption. Moreover, LSPR is also verified in wurtzite Cu 2 SnS 3 NCs, although the observed peak maximum is red-shifted comparing to the LSPR band of Cu 3 SnS 4 NCs. But the calculated free carrier concentration for Cu 2 SnS 3 by Drude model is on the same order of magnitude with Cu 3 SnS 4 in which sulfur vacancies acting as compensation centers could reduce hole density to some extent. Whereas Cu 2 ZnSnS 4 presents almost no absorption due to its relatively lower hole concentration. [ABSTRACT FROM AUTHOR]

• Semi-polar (11 2 ¯ 2) plane p-Al 0.21 Ga 0.79 N films were deposited with In surfactant. • A hole concentration as high as 4.8 × 1017 cm−3 was obtained. • The crystal quality of the p-AlGaN films could be improved with In surfactant. Indium (In) surfactant was applied during the growth process to improve the properties of the (11 2 ¯ 2) plane p-Al 0.21 Ga 0.79 N films. The characterization results demonstrated that the crystal quality of the (11 2 ¯ 2) plane p-AlGaN could be ameliorated with In surfactant. Meanwhile, the surface morphology as well as the hole concentration of the p-AlGaN films could be enhanced remarkably by optimizing the flow rate of TMIn. In particular, a maximum hole concentration of 4.8 × 1017 cm−3 was obtained for the p-AlGaN epi-layer when the TMIn flow rate was 1.12 μ mol/min, which was increased by 3 times compared to that for the epi-layer grown without In surfactant. [ABSTRACT FROM AUTHOR]

The effects of in-plane polarization change on the determination of the hole density of weakly under-doped (Bi, Pb)-2212 single crystals has been studied by x-ray absorption spectroscopy (XAS). The XAS signal at the CuL3 edge (925–940eV) and O K edge (525eV to 539eV) were recorded under continuous rotation of the CuO2 plane from 0° to 180° with a minimum increment of 1.8°, yielding experimentally an in-plane polarization dependence for the absorption signals at the respective threshold. From that the in-plane angular dependence of the hole density (n H (φ)) could be determined. Fermi׳s golden rule was then used for the evaluation of the in-plane polarization dependence showing the expected polarization independence in disaccord to the experimental observations. Possible scenarios to solve this issue are discussed. Our results propose that polarization dependence could be due to inhomogeneous distribution of holes in the CuO2 planes which is also supported by models. Second, the role of out of plane orbitals has to be taken into account for interpretation. [ABSTRACT FROM AUTHOR]

[Display omitted] • α -BaCu 2 Se 2 is a wide-band-gap semiconductor with orthorhombic structure. • Cu vacancy engineering was applied in Zintl α -BaCu 2 Se 2 aiming to improve the thermoelectric properties. • The Cu vacancy can realize the temperature-dependent hole concentration to the optimal one. • Cu vacancy engineering signifies the enlargement of average zT in a wide temperature range. Vacancy engineering offers an alternative route to aliovalent and interstitial doping for optimization of the carrier concentration in thermoelectric materials. For the wide-bandgap semiconductor BaCu 2 Se 2 , the Cu vacancy is dynamically stable; this feature can be rationally manipulated to maximize the thermoelectric figure of merit zT. In this work, we show that at room temperature, Cu-deficient BaCu 2− x Se 2 samples exhibit increased hole effective mass and mobility, attributed to the energy band modulation, which are favorable for improved electrical transport properties. More importantly, the defect energy level resulting from the Cu vacancies continually contributes holes at high temperature, thereby allowing the hole concentration to approach an optimal concentration. This effect leads to an increase of the power factors over a wide temperature range. The artificial reduction of the Cu content in BaCu 2 Se 2 results in the strengthened point-defect scattering, suppressing the lattice thermal conductivity. This strategy allows simultaneous optimization of the electrical and thermal transport properties, with a thermoelectric figure of merit zT = 1.08 achieved for BaCu 1.94 Se 2 at 823 K, which is 38% higher than that of stoichiometric BaCu 2 Se 2. Within the measured temperature range, the average zT value for BaCu 1.94 Se 2 is 0.494, which is 52.9% higher than that of BaCu 2 Se 2. [ABSTRACT FROM AUTHOR]

Highlights: [•] The electrochemical potentiostatic activation (EPA) method. [•] Improve the internal quantum efficiency of 385-nm ultraviolet light-emitting diodes. [•] Secondary ion mass spectroscopy indicates the successful removal of hydrogen atoms. [•] The light-output power was enhanced by ∼20% at an input current of 50mA. [•] The reverse leakage current was also lowered by ∼one order after the EPA process. [Copyright &y& Elsevier]

Abstract: Samples of Eu1−x Pr x Ba2Cu3O7−δ with compositions x=0.0, 0.1 and 0.3 were prepared by the solid state reaction route. The structural, electrical and microstructural properties were investigated by X-ray diffraction, Physical Property Measurement System (PPMS) and scanning electron microscopy (SEM) techniques respectively. The lattice parameters, oxygen deficiency, hole concentration in the CuO2 plane, average charge on Cu–O plane were evaluated from X-ray diffraction data. From XRD data, it is observed that the lattice parameters and oxygen deficiency increase with increasing Pr concentration. It was also observed that the hole concentration in CuO2 plane and average charge on Cu–O plane decrease with increasing Pr concentration. The electrical resistivity of all samples was measured in the temperature range 300K to 4K. It was found that the normalized transition temperature decreases with increasing Pr concentration. This may be due to reduction in hole concentration or average charge on Cu–O plane. From scanning electron microscopy images, it was observed that grain size increases with increasing Pr concentration. This increase may be the possible cause for suppression of T c. [Copyright &y& Elsevier]

Dependences of the superconducting transition temperature ( T) and chemical potential shift (Δ μ) on the hole concentration ( n) for LaSrCuO cuprate is obtained taking into account of canonical two-band BCS model containing Fermi surfaces of p and d holes. The shift of chemical potential ( μ) leads to the curve T( n) with a maximum. The dependences of T( n) for our system compared with available experimental results. Downward shift (Δ μ) of the electron chemical potential ( μ) with the hole concentration ( n) have been found. Self-consistent equations for superconducting order parameters ( $\bar{\Delta}_{p}$ and $\bar{\Delta}_{d}$) for both p and d holes are derived using Green's function and equation of motion method. The temperature dependences of superconducting gaps and specific heat based on this model are also calculated. The enhancement of T due to doping is observed. [ABSTRACT FROM AUTHOR]

Abstract: A method of Al2O3 deposition and subsequent post-deposition annealing (Al2O3-PDA) was proposed to passivate electrically active defects in Ge-rich SiGe-on-insulator (SGOI) substrates, which were fabricated using Ge condensation by dry oxidation. The effect of Al2O3-PDA on defect passivation was clarified by surface analysis and electrical evaluation. It was found that Al2O3-PDA could not only suppress the surface reaction during Al-PDA in our previous work [Yang H, Wang D, Nakashima H, Hirayama K, Kojima S, Ikeura S. Defect control by Al-deposition and the subsequent post-annealing for SiGe-on-insulator substrates with different Ge fractions. Thin Solid Films 2010; 518: 2342–5.], but could also effectively passivate p-type defects generated during Ge condensation. The concentration in the range of 1016–1018 cm−3 for defect-induced acceptors and holes in Ge-rich SGOI drastically decreased after Al2O3-PDA. As a result of defect passivation, the electrical characteristics of both back-gate p-channel and n-channel metal–oxide-semiconductor field-effect transistors fabricated on Ge-rich SGOI were greatly improved after Al2O3-PDA. [Copyright &y& Elsevier]

Abstract: A study of photoinduced high-T c superconductivity is presented by canonical two-band BCS model containing Fermi surfaces of p and d holes. We have obtained two superconducting gaps from this model. Studies of chemical potential and hole concentration dependences on critical temperature (T c ) are made. The enhancement of T c is found due to doping. The study of specific heat and density of states based on this model is also presented. The dependence T c (n h ) for the system YBa2Cu3O7−x (123) obtained theoretically agrees with the available experimental data. [Copyright &y& Elsevier]

Bulk superconductor samples of YBa2Cu3-xCoxO7-δ with x = 0, 0.01, 0.03, 0.05 are synthesized by solid-state reaction route. Both x-ray diffraction and electron microscopy have been employed to study the phase identification, intergrowths, dislocations and the local structure of these samples. Transition temperature of the samples has been determined by four probe resistivity measurements. The x-ray diffraction patterns indicate that the gross structure/phase of YBa2Cu3-xCoxO7-δ do not change with the substitution of Co up to x = 0.05. The zero resistance critical transition temperature [Tc(R = 0)] is found to decrease and critical current density (Jc) increases with the increased concentration of cobalt in the compound. The Jc enhancement for the cobalt doped samples may be resulting due to flux pinning from some defects such as planar defects, stacking faults and micro defects (twin, domains etc.) and the rapid suppression in Tc may be due to the cooper pair breaking and the hole filling in the CuO2 planes. [ABSTRACT FROM AUTHOR]

In this study, the contact characteristics of p-GaN treated by laser-assisted annealing with different laser fluences were investigated. Based on the two-photon absorption model, a laser treatment on the p-GaN was achieved by utilizing laser with a wavelength of 532 nm. The results showed that specific contact resistance decreased as the laser fluence increased in the low fluence region (<200 mJ/cm2), but deteriorated when the fluence reached to 300 mJ/cm2 or even higher, indicating that laser annealing by 532 nm could greatly affect specific contact resistance. The results of SIMS, photoluminescence spectra, and XPS measurements showed that the enhanced ohmic contact for samples with a low laser injection fluence was attributed to the enhanced aggregation of Mg atoms near the surface and the enhanced activation efficiency of Mg Ga acceptors by the removal of H atoms from Mg–H complexes. For the samples treated with fluence higher than 300 mJ/cm2, the contact characteristics were compromised due to both the accumulation of gallium oxide on the surface which increased the barrier height of metal/GaN and the formation of structural defects. An improved ohmic contact with a specific contact resistance of 2.93 × 10−4 Ω cm2 were demonstrated for p-GaN with the 200 mJ/cm2 laser fluence. 532 nm laser-assisted annealing treatment has great potential for the selective activation of p-GaN and enhancement of GaN/metal contact characteristics. [ABSTRACT FROM AUTHOR]

Abstract: We have investigated the effect of addition of Gd in Bi1.8Pb0.35Sr1.9Ca2.1Cu3Gd x O y superconductor with x=0, 0.1, 0.2, 0.3, 0.4 and 0.5. The samples were prepared by standard solid-state reaction methods. The investigation consisted of X-ray diffraction (XRD), scanning electron microscopy (SEM), dc electrical resistivity, hole concentration and transport critical current density measurements. Transport measurements indicated that the superconducting transition temperature, transport critical current density and hole concentration values of the samples strongly depend on the Gd addition. The values of T c, and J c of the samples decreased with the increase in Gd addition. When Gd addition ratio was increased, surface morphology and grain connectivity of the samples were observed to degrade from SEM investigations and phase ratio of the high-T c (Bi-2223) phase to the low-T c (Bi-2212) phase decreased (XRD measurements). The possible reasons for the observed degradation in superconducting and microstructure properties of Bi-2223 due to Gd addition were discussed. [Copyright &y& Elsevier]

Abstract: The local vibrational modes (LVMs) observed by Fourier transform infrared (FTIR) spectroscopy in GaAsN films grown by chemical beam epitaxy (CBE) was studied, and the influence of the nitrogen–hydrogen bond (N–H) concentration on the hole concentration was investigated. The absorption peak around 936cm−1 is suggested to be the second harmonic mode of the substitutional N, NAs, LVM around 469cm−1. The absorption peak around 960cm−1 is suggested to be the wagging mode of the N–H, where the stretch mode is observed around 3098cm−1. The hole concentration linearly increases with increasing N–H concentration, and the slope increases with increasing growth temperature. It indicates that the hole concentration in GaAsN film is determined by both the number of the N–H and unknown defect, such as impurities, vacancies, and interstitials. This defect concentration increases with increasing growth temperature, suggesting that it is determined by Arrhenius type reaction. [Copyright &y& Elsevier]

To address the structural mechanisms associated with Tc variations induced by Co doping, two samples of the nominal composition (Ga1-xCox)Sr2(Tm0.6Ca0.4)Cu2Oz with x = 0.5 and 0.7 have been prepared and studied by using neutron powder diffraction and transport measurements. In contrast to the x = 0.5 sample, which shows superconductivity around 35 K, the x = 0.7 sample does not exhibit superconductivity. The neutron powder diffraction studies indicate that both samples exhibit the 1212 structure with space group Ima2 and the Co atoms exclusively substitute for the Cu atoms located on the chain sites of the 123 parent structure. The depression in Tc of the x = 0.7 sample, compared to that of the x = 0.5 sample, is discussed in connection with oxygen content, disorder, and change in hole concentration on the superconducting planes. [ABSTRACT FROM AUTHOR]

Abstract: The effect of superconductivity and inhomogeneity on the phase coherence between superconducting grains for Bi2Sr2CaCu2O8+δ (Bi-2212) is discussed. We find that in the UD regime, inhomogeneity plays a central role in establishing the phase coherence between superconducting grains. By decreasing hole concentration, p, the phase stiffness for the thermal fluctuations is suppressed, whereas the phase coherence between the superconducting grains is enhanced. In particular, the phase coherence between the superconducting grains is established almost immediately as the superconductivity for Bi-2212 with p ≃0.075 appears. [Copyright &y& Elsevier]

The performance characteristics of green light-emitting diodes (LEDs) grown by metal-organic chemical-vapor deposition were investigated to study the dependence of the device performance on the materials and the growth conditions of p-type layer grown after the InGaN multiple-quantum-well active region. The electrical and structural qualities of Mg-doped p-In0.04Ga0.96N and p-GaN layers grown under different growth conditions were studied to optimize the growth conditions of p-type hole injection layers of green LEDs. A free-hole concentration of p=1.6times1018 cm-3 of with a resistivity of 0.33Omegamiddotcm was achieved for p-GaN:Mg layers grown at 1040degC. Lower hole concentrations and mobilities and rough surfaces were obtained when the growth temperature was decreased to 930degC in H2 ambient. In the case of p-In0.04Ga0.96N grown at 840degC in N2, a significant improvement of the hole concentration was achieved due to the reduced ionization activation energy of Mg acceptors in InGaN. Also we observed that as-grown p-GaN layers grown in N2 ambient showed p-type properties without Mg dopant activation. The electrical and optical properties of In0.25Ga0.75 N/GaN multiple-quantum-well green LEDs with such different p-layers were investigated. The electroluminescence intensity was improved for the LEDs with p-In0.04Ga0.96N layers grown at 840degC as compared to the LEDs with p-GaN layers grown at higher temperatures due to the reduced thermal damage to the active region, high hole injection, and low piezoelectric field induced in the active region. p-InGaN layers are very attractive candidates for the p-layer in green LED structures. The low temperature and N2 ambient used during the growth of InGaN layers are beneficial to protect the InGaN active region containing high-indium composition quantum-well layers in a- ddition to the advantage of providing a higher hole concentration. However, the LEDs with p-In0.04Ga0.96 N layer showed a slightly higher turn on voltage which could originate from the potential barrier for hole transport at the interface of the p-InGaN layer and the last GaN quantum-well barrier. to reduce this problem, we designed and characterized an LED structure having a graded indium composition in the p-In0.04Ga0.96N layer in order to improve hole transport into the active region. Optimized LEDs with p-InGaN layers grown in a N2 ambient showed much brighter electroluminescence due to low damage to the active region during p-InGaN layer growth [ABSTRACT FROM PUBLISHER]

Abstract: We have investigated the effect of Zn substitution on the hole content, p, and the oxygen deficiency, δ, for a series of high-quality crystalline c-axis oriented thin films and polycrystalline Y1−x Ca x Ba2(Cu1−y Zn y )3O7−δ compounds over a wide range of composition (x, y, and δ). p was determined from the room-temperature thermopower, S[290K]. When annealed at a given temperature and oxygen partial pressure, a small but systematic variation in S[290K] was observed with Zn, for all the samples. From the analysis of the temperature derivative of resistivity, dρ/dT, at 300K, which varies almost linearly with p, irrespective of the composition of the sample, and the thermo-gravimetric analysis (TGA), we have found that annealing under identical conditions makes the Zn-substituted compounds somewhat more oxygen deficient compared to the Zn-free ones. [Copyright &y& Elsevier]

Abstract: The electrical and optical properties of Mg-doped In x Ga1−x N were investigated herein. With an In mole fraction increase, the RT carrier concentration was increased exponentially. Compared to Mg-doped GaN layers, it was found that we could achieve a high (1.65×1019 cm−3) hole concentration from the p-type InGaN with an indium content of 0.23. InGaN/GaN MQW blue LEDs without and with a 5-nm-thick p-type In0.23Ga0.77N contact layer were also successfully fabricated. We could reduce the 20 mA operation voltage from 3.78 V to 3.37 V by introducing a 5-nm-thick In0.23Ga0.77N layer on top of the p-type GaN layer and improve the blue LED EL intensity and output power by employing such a p-In0.23Ga0.77N layer. [Copyright &y& Elsevier]