Search

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]

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.

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 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]

• 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]

[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]

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]