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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]